View source for Operation Hardtack I

{{Short description|Series of 1950s US nuclear tests}}
{{Use mdy dates|date=November 2018}}
{{Infobox nuclear weapons test
 |name                = Operation Hardtack I
 |picture             = [[File:Hardtack Teak.gif|300px]]
 |picture_description = Hardtack I-''Teak'', 3.88 megatons.
 |country             = United States
 |test_site           = {{plainlist|
* Bogallua (Alice), Enewetak Atoll
* Eninmen (Tare), Bikini Atoll
* Enjebi (Janet), Enewetak Atoll
* Johnston Island, Johnston Atoll
* Namu (Charlie), Bikini Atoll
* Pacific Proving Grounds
* Pokon (Irvin), Enewetak Atoll
* Runit (Yvonne), Enewetak Atoll
* Teiter (Gene), Enewetak Atoll
* Yurochi aka Irioj (Dog), Bikini Atoll}}
 |period              = 1958
 |number_of_tests     = 35
 |test_type           = {{ubl|Air drop|Balloon|Barge|Dry surface|High-altitude rocket<br />{{convert|30|-|80|km|ft|abbr=on}}|[[Underwater explosion|Underwater detonation]]}}
 |max_yield           = {{convert|9.3|MtonTNT|lk=in}}
 |previous_series     = [[Project 58/58A]]
 |next_series         = [[Operation Argus]]
}}
{{GeoGroup|article=Operation Hardtack I}}
'''Operation Hardtack I''' was a series of 35 nuclear tests conducted by the United States from April 28 to August 18 in 1958 at the [[Pacific Proving Grounds]].<ref name=LT_1 /><ref name=CW_1/>{{rp|page=212}} At the time of testing, the Operation Hardtack I test series included more nuclear detonations than the total of prior nuclear explosions in the Pacific Ocean.<ref name=CW_2/>{{rp|page=1}} These tests followed the ''[[Project 58/58A]]'' series, which occurred from 1957 December 6 to 1958, March 14, and preceded the [[Operation Argus]] series, which took place in 1958 from August 27 to September 6.<ref name=CW_1/>{{rp|pages=212–214}}

Operation Hardtack I was directed by Joint Task Force 7 (JTF 7). JTF-7 was a collaboration between the military and many civilians, but was structured like a military organization. Its 19,100 personnel were composed of members of the US military, federal civilian employees, as well as workers affiliated with the [[United States Department of Defense|Department of Defense]] (DOD) and the [[United States Atomic Energy Commission|Atomic Energy Commission]] (AEC).<ref name=CW_2/>{{rp|page=1}}

There were three main research directions. The first was the development of new types of nuclear weapons. This was undertaken by detonating experimental devices created by the AEC's [[Los Alamos National Laboratory|Los Alamos Scientific Laboratory]] and the [[Lawrence Livermore National Laboratory|University of California Radiation Laboratory]] (UCRL). The DOD performed experiments and tests on these detonations that did not hamper the AEC's research. The second research direction was to examine how underwater explosions affected materiel, especially Navy ships, and was performed by the DOD. The Wahoo test was conducted in the open ocean, whereas Umbrella was in a lagoon.<ref name=CW_2/>{{rp|page=1}} The final avenue of study was to analyze high-altitude nuclear tests to refine the detection of high-altitude nuclear tests and investigate defensive practices for combatting ballistic missiles. This research direction was composed of three individual tests and were the first high-altitude tests. The individual tests in the series were Orange, [[Hardtack Teak|Teak]], and Yucca. Orange and Teak were known collectively as Operation Newsreel and were rocket boosted. Yucca reached its altitude using balloons.<ref name=LT_1 /><ref name=CW_1/>{{rp|page=187}}<ref name=CW_2/>{{rp|page=3}}

[[File:Hardtack I Poplar 001.jpg|thumb|Aerial shot of the explosion during Hardtack I Poplar. [[Martin RB-57D Canberra|Martin RB-57D]] in the foreground.]]

==Historical background==
Many events and proceedings leading up to Operation Hardtack I, such as previous nuclear testing results and the global political atmosphere, influenced its creation and design. One such historical circumstance was that nuclear radiation concerns were mounting publicly and abroad by 1956. During the [[1956 United States presidential election|1956 Presidential Election]], ending nuclear testing was a campaign issue and nuclear safety was one part of that discussion. At the same time, the [[Soviet Union|Union of Soviet Socialist Republics]] (USSR) was publicly proposing a moratorium on testing.<ref name=CW_1/>{{rp|page=149}}

In 1956 during June, the [[National Academy of Sciences]] (NAS) recommended new radiation exposure limits for the general public in a report entitled: "The Biological Effects of Atomic Radiation".<ref name=CW_1/>{{rp|page=153}} The AEC, which was the body that developed nuclear weapons,<ref name=CW_3/>{{rp|page=3}} accepted the NAS recommended radiation exposure limits. Some AEC members asserted that the limits were reached incorrectly and should be reviewed in the future. Charles L. Dunham, AEC Director of the Division of Biology and Medicine (DBM), said that the new limits of nuclear radiation exposure would prevent them from continuing testing in Nevada. Dunham, in association with other AEC offices and officials, made recommendations to move further tests to the Pacific to eliminate the need to determine radiological fallout safety.<ref name=CW_1/>{{rp|page=154}}

Also in 1956, the AEC was designing a test series that included nuclear detonations which would release significant amounts of nuclear fallout. The series came to be known as [[Operation Plumbbob]] and took place in 1957 from April 24 to October 7. Operation Plumbbob was followed by Project 58/58A and Operation Hardtack I. At the time of testing, Operation Plumbbob was the most extensive nuclear test series held at the Nevada Test Site.<ref name=CW_1/>{{rp|page=159}} President [[Eisenhower]] was very cautious in approving Plumbbob due to public concern.<ref name=CW_1/>{{rp|page=157}} Consequently, the AEC held brief and ultimately fruitless discussions of moving some of the tests in the Plumbbob series to the next planned Pacific Ocean series, Operation Hardtack I, to minimize radioactive fallout in and around the Nevada Test Site.<ref name=CW_1/>{{rp|page=155}}

When Operation Plumbbob began in the spring of 1957, the planning process of Operation Hardtack I was well underway and the number of nuclear detonations planned were more than those in the Plumbbob series.<ref name=CW_1/>{{rp|page=183}} At the same time, radiation and nuclear proliferation concerns around the world had led to formal discussions between the US, USSR, and other countries on the topic of instituting a global ban on nuclear testing as a path to disarmament. In 1957 on August 9 AEC chairman [[Lewis L. Strauss]] proposed to President Eisenhower a preliminary plan of Operation Hardtack I. President Eisenhower objected to the length of the four-month testing period and that the plan called for 25 shots,<ref name=CW_1/>{{rp|page=183}} which was one more than in Plumbbob.<ref name=CW_1/>{{rp|page=161}} As a result of the discussion, Eisenhower consented to yields no larger than {{convert|15|MtonTNT}}, and ordered that the testing period be as brief as possible.<ref name=CW_1/>{{rp|page=183}}

Project 58/58A followed Operation Plumbbob and began almost two months later starting in 1957 on December 6. Project 58/58A was composed of four safety tests; they were not supposed to result in nuclear radiation. All four took place at the Nevada Test Site. The safety tests were intended to ensure that the bombs would not malfunction. However, the test named Coulomb-C which took place in 1957 on December 9 did malfunction. It resulted in an unanticipated {{convert|500|tonTNT}} blast. The blast released a nuclear radiation fallout cloud that traveled toward [[Los Angeles]] and resulted in low levels of nuclear radiation. The bomb failure added to public concern over nuclear testing's safety.<ref name=CW_1/>{{rp|page=186}}

Some tests were cut in an effort to meet Eisenhower's demands for a shorter testing period, but new tests quickly filled their place. AEC chairman Strauss remarked that the large number of shots was due to the "DOD's requirement for an increasing number of different nuclear weapons types".<ref name=CW_1/>{{rp|page=187}} Eisenhower eventually approved the plan for Operation Hardtack I in late January, even though it still contained 25 shots. On March 31, 1958, the USSR announced a suspension of all tests and called on the US to do the same. On May 9 the leader of the Soviet Union, [[Nikita Khrushchev]], accepted Eisenhower's invitation for technical discussions on a nuclear testing moratorium and negotiations began on July 1 of the same year. Eisenhower announced to the US on August 22, 1958, that the ban would begin October 31. US scientists responded by seeking to add more tests to the Hardtack Series in case it turned out to be the last chance. Consequently, Operation Hardtack I consisted of 35 tests.<ref name=CW_1/>{{rp|pages=189–190}}

There was public health concern with the number of shots in Operation Hardtack I.<ref name=CW_3/>{{rp|page=23}} Studies released in March 1958 indicated that people as far as {{convert|400|mi|nmi km|sp=us}} away could have severe retinal burns from two of the three high-altitude tests: Teak and Orange.<ref name=CW_1/>{{rp|page=187}}<ref name=CW_3/>{{rp|page=257}} It was then decided that they would be moved to [[Johnston Island]], which was {{convert|538|mi|nmi km|sp=us}} from the nearest inhabited island. The high-altitude nuclear tests delivered the first openly reported man-made high-altitude [[Nuclear electromagnetic pulse|electromagnetic pulses]] (EMP). Teak, which was detonated at {{convert|252000|ft|km|sigfig=3}} and was {{convert|3.8|MtonTNT}}, produced an [[aurora]]-like effect that was visible from [[Hawaii]], {{convert|700|nmi|mi km}} displaced from the detonation. Most radio communications immediately dropped across the Pacific Ocean. The blackout in Australia lasted for 9 hours and Hawaii's lasted for no less than 2 hours.<ref name=CW_3/>{{rp|page=266–269}}

== High-altitude tests ==
{{See also|High-altitude nuclear explosion|List of United States' nuclear weapons tests}}

Operation Hardtack I contained three high-altitude tests called Operation Newsreel that were designed to study many effects that a [[Nuclear weapon|nuclear]] explosion would have on materials and electronic systems. They were also used to test the energy of the explosion and what forms of energy they would produce. Yucca was the name of the first high-altitude test and it was performed near the [[Enewetak Atoll]] in the Marshall Islands. The other two high-altitude tests, Orange and Teak, were performed near the [[Johnston Atoll]] in the South Pacific Ocean about {{convert|1300|km|mi nmi|}} southwest of the Hawaiian Islands.<ref name=CW_3/>{{rp|page=251}}

=== Impact on ozone layer ===
There was some uncertainty on whether detonating a nuclear weapon at such high altitudes would cause a hole in the [[ozone layer]]. After multiple [[Underwater nuclear testing|underwater tests]] there was evidence to show the energy created by the blast would create [[ozone]]. Project leads determined some destruction of ozone would occur which would then be replaced by the ozone created from the explosion. It was agreed that if this theory were wrong, the hole created in the ozone layer would be minuscule enough to cause no harm. Upon completion of Operation Newsreel, it was determined that there was very little evidence of any harm being caused to the natural ozone layer.<ref name=LT_215 />

=== Yucca ===
Yucca was the first high-altitude test performed during Operation Hardtack I and was detonated on April 28, 1958. It was lifted by a balloon to an altitude of {{convert|86000|ft|km|sigfig=3|sp=us}} and had a yield of {{convert|1.7|ktonTNT}}.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=251}}To achieve the altitude needed, the device was attached to a large helium-filled balloon which carried it to the detonation altitude. Due to issues with high winds on Enewetak Island, the balloon launches from ground were unsatisfactory, thus creating the need for a new method. The balloons were then deployed from an aircraft carrier which helped with deployment and the inflation. While the balloons were inflated, they were unable to take too much force from wind or the plastic material of the balloons would tear. While the balloons were inflating on the aircraft carrier, the ship could match and oppose the wind speed allowing for the balloon to be inflated in still air. To make sure the launch would be successful 86 balloon launches were tested.<ref name=CW_3/>{{rp|page=252}}

Due to concerns of failures, many safety measures were employed. While on ground, the bomb used multiple pins to prevent certain safety features of the bomb from being deployed before liftoff. One such pin was used to stop the electrical systems so that the bomb would be unable to be armed. In case of a dud, the bomb would detach from the balloon and be allowed to drop into the ocean where many more safety features would come into action. Some of these features included probes which could detect saltwater which would destroy the electrical system so the conductive seawater could not cause a short which would detonate the bomb. Another concern was a nuclear device floating in the ocean should a misfire occur. To combat this, inserts were created which would dissolve in a few hours, thus scuttling the device.<ref name=CW_3/>{{rp|pages=253–254}}

On the day of the launch many [[Meteorology|meteorological]] aspects were taken into account and calculations were done to ensure the bomb would reach the correct altitude. The bomb was loaded onto an aircraft carrier and preparations began. As the balloon was inflated multiple testing devices were connected to the balloon. The readings from these devices would be sent to multiple ships and aircraft so nothing would need to be recovered after the explosion. After all the preparations were done and the balloon was inflated, the device was released and began to climb. After almost three and a half hours of climbing the bomb was detonated at an altitude of {{convert|26.2|km|mi|sp=us}}. The aircraft carrier which carried Yucca was approximately {{convert|4|km|mi|sp=us}} from the detonation site. The shock wave from Yucca reached the carrier 3 minutes and 16 seconds after detonation.<ref name=CW_3/>{{rp|pages=255–257}}

The Yucca test had many [[United States Department of Defense|Department of Defense]] projects attached to it for research purposes. Alongside testing the use of a balloon carrier, the Department of Defense wanted to research the [[Electromagnetism|electromagnetic]] waves emitted from a nuclear explosion. This test would be used to determine the impact a nuclear explosion would have on [[Electronics|electronic]] devices. All of the data from these Department of Defense projects would be stored on recording devices on surrounding islands and in aircraft so data would not have to be recovered after the test.<ref name=CW_3/>{{rp|pages=253–254}} However, Yucca was carrying five different transmitting devices in canisters to help with research. While the balloon proved to be a great success, no data from the canisters were able to be retrieved due to equipment issues onboard one of the aircraft carriers.<ref name=CW_4/>{{rp|page=201}}

=== Teak ===
The [[Hardtack Teak|Teak]] test was launched from [[Johnston Island]] on July 31, 1958, and carried a payload of {{convert|3.8|MtonTNT}}.<ref name=CW_2/>{{rp|page=3}}<ref name=CW_3/>{{rp|page=251}} Teak was the second high-altitude test after the success of Yucca. Instead of a balloon, the warhead for the Teak test would be carried by a [[Redstone missile]]; a modified Redstone missile had been used to launch [[Explorer I]] in January of the same year.<ref name=CW_3/>{{rp|pages=256–257}} Other nuclear weapons had been tested using the Redstone missile, but until this time the highest payload to have been detonated was {{convert|3|ktonTNT}} during [[Operation Teapot]].<ref name=CW_4/>{{rp|page=218}} Teak would be the first high-altitude test to have a payload in the megaton range. The test was scheduled to take place from the [[Bikini Atoll]]. Due to the fact that the payloads of Teak and Orange were much larger than previous high-altitude shots, the test was moved to Johnston Island as to protect nearby native islanders from any retinal damage. As both Teak and Orange had been relocated these two tests were named Operation Newsreel. The name Newsreel came from the fact that these two tests were being moved to Johnston Island.<ref name=CW_3/>{{rp|page=259}}{{clarify|How does moving to Johnson inspire the name Newsreel?|date=June 2020}}

The safety precautions taken by the teams involved were precisely detailed. The day before the launch 187 team members would evacuate Johnston Island with 727 men the day of the test. This was to keep as few men on the island while still being able to operate the airfield and critical data instruments. Another problem the team members were concerned about was the issue of retinal damage. Since the payload of the bomb was so large, aircraft were scheduled to keep any civilian ships out of a {{convert|760|km|mi|sp=us}} radius of Johnston Island. Additionally, the [[Civil Aeronautics Authority]] was informed that it would be dangerous for any aircraft to fly within {{convert|965|km|mi|sp=us}} of Johnston Island. On the day of the test only about 175 men remained on Johnston Island to prepare for Teak to be launched and other various duties needed after.<ref name=CW_3/>{{rp|page=262–263}}

At 11:47 PM on July 31 Teak was launched; after 3 minutes it was detonated. Due to programming issues, the warhead detonated directly above Johnston Island.<ref name=CW_4/>{{rp|page=219}} At time of detonation the rocket had flown to an altitude of {{convert|76.2|km|mi|sp=us}}. The explosion could be seen from Hawaii {{convert|1297|km|mi|sp=us}} away and was said to be visible for almost half an hour. After the explosion, high frequency long-distance communication was interrupted across the Pacific. Due to this communication failure Johnston Island was unable to contact their superiors to advise of the test results until about eight hours after the detonation. Thirty minutes after detonation, a crew was sent out to collect the pod which had detached from the missile carrying the warhead. The pod had been [[Irradiation|irradiated]] and to handle it the crew members used disposable gloves in an attempt to protect themselves from [[beta radiation]].<ref name=CW_3/>{{rp|pages=265–270}}

During the Teak test all crew on and around Johnston Island were given protective eyewear to prevent [[flash blindness]] from the explosion. After the explosion it was found that besides the hazard of blindness, thermal radiation was another concern—even at an altitude of {{convert|76|km|mi|sp=us}}. A crew member who was on Johnston Island at the time was said to have received a slight sunburn from the amount of thermal radiation which had reached the island. While only slight to the crew member it created issues for the local fauna. Many birds were seen on Johnston Island in distress. Unsure if this was caused by blindness or thermal radiation, the project members decided to take precautions to protect local wildlife during the Orange test.<ref name=LT_215 />

=== Orange ===
Orange was launched twelve days after Teak on August 11, 1958.<ref name=CW_3/>{{rp|page=251}} Orange, like Teak, was launched using a Redstone Missile and had a yield of {{convert|3.8|MtonTNT}}.<ref name=CW_2/>{{rp|page=3}}<ref name=CW_3/>{{rp|page=271}} The same safety precautions used by Teak were implemented for the Orange launch. Seeing how smoothly the evacuation for the Teak launch went, it was decided that the evacuation did not need to occur the day before the launch and eight hundred and eight men were evacuated on August 11 to an aircraft carrier about {{convert|70|km|mi|sp=us}} northeast of the island. Along with protection for the project crew, it was decided after Teak that Sand Island, a local bird refuge, would need protection from the blast as well. To make sure that most of the wildlife was safe a smoke screen was created over Sand Island. Due to interest in Hawaii, it was announced on August 11 that there would be a nuclear test sometime between 10 PM and 6 AM.<ref name=CW_3/>{{rp|page=271}}

The rocket carrying the warhead was launched at 11:27 from Johnston Island and traveled south. Like Teak, the flight lasted 3 minutes and was detonated at 11:30 PM about {{convert|41|km|mi|sp=us}} south of Johnston Island at an altitude of about {{convert|43|km|mi|sp=us}}.<ref name=CW_3/>{{rp|page=271}}The trajectory of Orange was a major success after the incident with Teak being detonated directly over the island.<ref name=CW_4/>{{rp|page=219}} The recovery crew for the pod that was with Orange was unable to locate the research pod which had been launched with the rocket. Although Orange was visible from Hawaii it was not the great spectacle Teak had been. The light from the blast was visible for about 5 minutes. The explosion had also been slightly obscured to the crew at Johnston Island by cloud coverage. The blast from Orange did not cause the large communication interruption that Teak had caused, but some commercial flights to Hawaii were said to have lost contact with air traffic controllers for a short period of time.<ref name=CW_3/>{{rp|page=271}}

== Surface tests ==
Of the 35 nuclear tests in Operation Hardtack I, four were surface burst shots: Cactus, Koa, Quince and Fig. These tests took place from May to August 1958, all at the [[Enewetak Atoll]]. Surface tests inherently present the potential for more radioactive exposure issues than the high-altitude or underwater detonations. This is because there is more material present to be converted to radioactive debris by excess neutrons due to the proximity to the Earth's surface, and due to the soil and other minerals excavated from the craters created by these blasts. The existence of this extra material allows for larger radioactive particles to be created and lifted into the blast cloud, falling back to the surface as fallout.<ref name=CW_3/>{{rp|page=28}}Though surface and near-surface tests have a higher probability of radioactive exposure problems, the radioactive elements have significantly shorter residence times when injected into the atmosphere. As radioactive clouds from surface-type tests reach heights of around {{convert|20|km|mi|sp=us}} at maximum, and thus cannot extend higher than the lower stratosphere, the residence times can be up to 13 years less than the [[High-altitude nuclear explosion|high-altitude]] blasts.<ref name=LT_215 />{{rp|38}} During original concept planning in 1954, Enewetak was supposed to be the location of the smaller tests conducted during Operation Hardtack I. Due to poor weather conditions and policy changes in 1958, five of the [[UCRL]] tests which were planned to be conducted at the [[Bikini Atoll]] were moved to Enewetak. This included the later two surface blast devices in the Quince and Fig tests.<ref name=CW_3/>{{rp|pages=149–187}}

=== Cactus ===

[[File:Operation_Hardtack_I_Cactus_shot_crater,_Runit_Island,_Enewetak_Atoll.jpg|thumb|Operation Hardtack I Cactus shot Crater on [[Runit Island]]]]

The Cactus test took place May 6, 1958 at approximately 0615. An {{convert|18|ktonTNT}} land-surface type shot was detonated on a platform at the northern tip of [[Enewetak Atoll|Runit]], Enewetak in the second of the 35 tests for Operation Hardtack I.<ref name=CW_3/>{{rp|page=2}}The initial cloud from the explosion reached as high as {{convert|19000|ft|km|sigfig=3|sp=us}} within the first ten minutes, and settled at around {{convert|15000|ft|km|sigfig=3|sp=us}} by 20 minutes after detonation. The nuclear fallout prediction map proved to be accurate in determining the span and the intensity of the resultant fallout.<ref name=CW_3/>{{rp|pages=149–187}}Measured peak intensity of fallout reached {{val|440|u=R}} at hour three directly above blast site on the North end of the Atoll. At mid-island the radiation was measured to be {{val|1.7|u=R}}. The southern tip received a very small amount of radiation, {{val|0.005|u=R}} due to the easterly winds.

Out of the eight Programs listed, DOD-affiliated Projects 1.4, 1.7, 1.8, 1.9, 1.12, 2.8, 3.2, 5.2, 5.3, 6.4, 6.5 and 6.6 involved the Cactus test.<ref name=CW_3/>{{rp|page=149–187}}

One of the goals of this test was to study the physical characteristics of the crater and the surrounding area pre- and post-detonation associated with Project 1.4. A camera was mounted to a RB-50 aircraft and the resultant crater was mapped using photogrammetry. Measurements were taken from {{convert|500|ft|m|sigfig=3|sp=us}} down to ground zero for both pre- and post detonation. Survey measurements of the Cactus test could not be made until the resultant radiation amounts had lowered to safer levels.<ref name=CW_3/>{{rp|pages=114–138}} Along with photogrammetric radial measurements, Airblast measurements were also recorded near surface zero for Cactus in accordance with Project 1.7. Similar to Project 1.8, Project 1.9 sought to determine transmission of blast pressure through the ground soil. Forty-three drums were buried at varying depths {{convert|600|ft|m}} from ground zero of the Cactus detonation. Individuals from the [[Air Force Ballistic Missile Division]]—TRW Space Technologies Laboratory sought to the Shock Spectra Studies of Project 1.12. Measurement gauges were located between {{convert|625|and|965|feet}} from the blast site. Fallout measurements and samples were taken by aircraft in the aftermath of the detonation, as part of Project 2.8. These surveys were designed in part to determine the impact of specific radionuclides to overall nuclear fallout. Samples were taken early post-blast using a new rocket sampler, the [[UCRL]], which were then followed by [[Martin B-57|B-57D]] and [[Boeing B-50 Superfortress|WB-50]] aircraft. Between four and twenty-four hours post-detonation, the WB-50 collected several samples at {{convert|1000|ft}} in altitude. Project 3.2 involved structural tests of corrugated steel arches. One of these arches was placed {{convert|980|ft|m}} away from the Cactus blast site. Eight days after the test, a crew of 13 men were allowed near the surface zero in order to extract the arch. The extraction took around twelve hours, and the radioactivity levels reached a maximum at {{val|0.420|u=R/hr}} during this time. Project 5.2 sought to determine the effects of the blast on two [[Douglas A-4 Skyhawk|A4D-1]] aircraft, both in thermal radiation and pressure. Nine film badges were placed throughout each aircraft in order to measure radiation. The Gamma [[dosimeter]] worn by the pilot in aircraft 827 indicated a neutron exposure level of {{val|0.105|u=rem}}. There is not information available for the dosimeter worn by the pilot in aircraft 831. Radiation recorded by six of the nine film badges ranged from {{val|0.49|u=R}}{{hyphen}}{{val|1.74|u=R}}. Information from the remaining three film badges, located at the Pilot's right leg, left sleeve, and left vest is not available. The pilot's exposures were both greater than {{val|3|u=R}}.  Project 5.3 was very similar to 5.2, focusing on the effects of the blast on the structure of two test [[North American FJ-4 Fury|FJ-4]] aircraft. Radiation from film badges on aircraft 467 ranged from {{val|0.52|u=R}}{{hyphen}}{{val|3.71|u=R}}, and {{val|1.23|u=R}}{{hyphen}}{{val|5.06|u=R}} for aircraft number 310. In Project 6.4, the Army Signal Research and Development Laboratory (SRDL) investigated the [[Electromagnetism|electromagnetic]] pulses post-detonation, using two instruments, one at [[Wotho Atoll|Wotho]] (roughly {{convert|240|nmi|mi km}} from Enewetak) and one at Kusaie (around {{convert|440|nmi|mi km}} from Enewetak). Though Cactus is mentioned in Project 6.5, whose goal was to study the radar echoes from the fireball, it is not clear what destroyers were involved if any. Destroyers for the Teak, Fir and Yucca tests are explicitly stated. Project 6.6, the last of the projects that involved the Cactus test, sought to measure the physical properties of the stabilized radioactive cloud following the blast.<ref name=CW_3/>{{rp|pages=114–138}}

=== Koa ===
At 06:30 on May 13, the Koa surface device was detonated at the western side of Dridrilbwij. The size of the blast was {{convert|1.37|MtonTNT}}, around 76 times larger than the yield of the previous surface test, Cactus. The test was conducted in a large water tank. Within 17 minutes of the blast, surface clouds reached approximately {{convert|60000|ft|km|sp=us}}. [[Nuclear fallout]] predictions for Koa were larger and covered a broader range than Cactus, with significantly higher radiation levels, an order of magnitude larger, in the immediate region surrounding the blast.<ref name=CW_3/>{{rp|page=44}} There had been a larger nuclear barge detonation, the {{convert|1.85|MtonTNT}} Apache test, off the island of Dridrilbwij two years prior in 1956, during which the island survived.<ref>Military Effects on Operation REDWING : AFSWP and Joint Task Force 7 : Free Download & Streaming : Internet Archive. (n.d.). Retrieved April 17, 2016, from https://archive.org/details/MilitaryEffectsonOperationRedwing1956</ref> The detonation of the Koa device, however, caused complete destruction of the island.<ref name=CW_3/>{{rp|page=44}}

The Department of Defense (DOD) sponsored a series of experiments for Koa: Projects 1.4, 1.7, 1.8, 1.9, 1.12, 2.9, 3.2, 3.6, 5.1, 5.3. 6.4, 6.5, 6.6, 6.9. and 6.11.<ref name=CW_3/>{{rp|pages=149–187}} Project 1.4, which sought to study land craters post detonation for several shots, took ground survey measurements from surface zero out to {{convert|2,500|ft|m|sp=us}}. Detailed measurements could not be made until four days after the blast due to radiation levels. Using a boat, the majority of the crater was mapped, though some measurements could not be made until 1959 due to radioactivity levels around the Koa blast site. In Project 1.9, the blast-induced pressure through the soil was measured by burying 43 drums at depths ranging from {{convert|0|to|20|ft|m}} and around {{convert|3000|ft|m|sp=us}} feet from the Koa blast site. The early radioactive cloud samples, normally collected post-shot as a part of Project 2.8 using a UCRL rocket sampler, were not collected after the Koa test due to technical difficulties. Fallout at high and low altitudes using B-57D and WB-50 aircraft were measured with no technical problems. Project 3.6, which was conducted only on Koa, tested the effects of the blast on reinforced-concrete slabs buried close to surface zero. One station was located at {{convert|1830|ft|m|sp=us}} from the blast site, and the other was located {{convert|3100|ft|m|sp=us}} away. Project 5.2 was designed to measure the radiation levels using film badges on different areas of the aircraft and on the pilot directly. Koa had the lowest average radiation measurements of the eight shots on this project, with aircraft 827 ranging from 0.01-0.02R and aircraft 831 reporting levels between 0.03-0.19R. Unlike in the Cactus test, all nine film badges from both aircraft were successfully recovered and reported.<ref name=CW_3/>{{rp|pages=114–138}}

=== Quince and Fig ===
Quince and Fig were a series of surface shots that occurred in early August at the center of Runit. They were the last of the Hardtack tests conducted at the Enewetak Atoll. Quince was detonated at 2:15pm on August 6, 1958. Twelve days later, the Fig device was detonated on August 18, 1958, at 4:00pm. Quince and Fig were UCRL devices with co-sponsorship through the DOD and the AEC, though the main focus of these tests was weapons development. One of the main differences between these two tests was that over 130 tons of soil from the [[Nevada Test Site]] had been shipped in and was placed at surface zero of the Fig test. The radioactive cloud from the Quince blast rose to {{convert|1500|ft|m|sp=us}}.  As Runit was to also be the detonation site for Fig, the area had to be decontaminated after the Quince test. Around {{convert|3|to|5|in|mm}} of contaminated topsoil was removed from an area {{convert|75|by|25|ft|m}} upwind of ground zero. An area of {{convert|60|sqft}} at the blast site was scraped to remove the top three inches of soil as well. Even with these precautions, the measured alpha activity was around 20,000 [[counts per minute]] (CPM), and the area closest to surface zero was roped off to prevent personnel from entering. Upon detonation, the mushroom cloud produced by the Fig device rose to approximately {{convert|6000|ft|km|sp=us|sigfig=2}}, with a base of roughly {{convert|4300|ft|km|sp=us|sigfig=2}}. Thirty minutes post detonation, radiation measurements at the blast site reached over 10,000 R/hr.<ref name=CW_3/>{{rp|pages=219–222}}

The DOD experiments for Quince and Fig included Projects 1.4, 1.7. 2.4, 2.9, 2.10, 2.11, 2.14. and 8.7.<ref name=CW_3/>{{rp|pages=219–222}}

== Barge tests ==
Barge mounted test detonations was a technique first used in 1954, and also compensated for the lack of land at {{Clarify |date= December 2023 |reason= article doesn't define what the initialism "HP" means |text= the HP.}} When testing returned to [[Bikini Atoll|Bikini atoll]] the use of barges as the shot point had begun, with one notable advantage, no radioactive surface zero areas were developed. Two large underwater craters were formed in 1954 and these were used as subsequent surface zeros for detonations fired from barges. This allowed the available land area to be used for the placement of measurement instrumentation and reuse of the same burst point without the long delays required for radiological cooling by natural decay or expensive and long decontamination procedures. Reuse of zero points also allowed reuse of instrument locations and recording shelters for several tests saving construction costs and time and increasing test-scheduling flexibility. In HARDTACK the 26 barge events used only five detonation areas.<ref name=CW_2/><ref name=CW_3/>

===Fir===
FIR predicted fallout, surface radiological exclusion (radex) areas, ship position, and aircraft participation. FIR was the first Bikini detonation of the Hardtack series. Detonated at 0550 on May 12, 1958. Fır was detonated on a barge in the Bravo crater, producing a {{convert|1.36|MtonTNT}} yield range.<ref name=CW_2/> After detonation, the cloud rose to {{convert|60000|to(-)|90000|ft|km|sigfig=3}}. The FIR detonation was shortly followed by BUTTERNUT detonation on Enewetak 25 minutes later. DOD-sponsored experiments for FIR included Projects 3.7, 5.1, 6.4, 6.5, 6.6 and 6.11.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=152}}

===Butternut===
BUTTERNUT predicted fallout, surface radiological exclusion areas (radex), ship positions, and aircraft participation. Butternut was detonated at 0615 on May 12, 1958, 25 minutes after FIR had been detonated at Enewetak. BUTTERNUT was detonated on a barge {{convert|4000|ft|km|sp=us|sigfig=3}} west of [[Runit Dome|Runit]], producing a yield range of {{convert|81|ktonTNT}}.<ref name=CW_2/> The cloud rose to {{convert|35000|ft|km|sp=us|sigfig=2}}, stabilizing at {{convert|30000|ft|km|sp=us|sigfig=2}}. The DOD-sponsored experiments for BUTTERNUT were Projects 5.1, 5.2, 5.3, 6.5, 6.6, and 6.9.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=152}}

===Holly===
HOLLY predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. HOLLY was detonated at 0630 on May 21, 1958, on a barge west of Runit, {{convert|4000|ft|km|sp=us|sigfig=3}} from the nearest edge of the island, producing a {{convert|5.9|ktonTNT}} yield range.<ref name=CW_2/> The detonation produced a {{convert|15000|ft|km|sp=us|sigfig=2}} cloud that stabilized at an altitude of {{convert|12000|ft|km|sp=us|sigfig=2}} at the top and {{convert|7500|ft|km|sp=us|sigfig=2}} at its base. Project 6.6, was the only DOD-sponsored experiment for HOLLY, and was conducted on Enewetak Island.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=192}}

===Nutmeg===
NUTMEG predicted fallout, surface radiological exclusion area (radex), ship positions, and aircraft participation. The second [[Bikini Atoll|Bikini]] shot, NUTMEG, was detonated at 0920 on May 22, 1958. NUTMEG was detonated on a barge in the [[Operation Redwing|ZUNI crater]], and produced a {{convert|25.1|ktonTNT}} yield range.<ref name=CW_2/> The detonation cloud stabilized at {{convert|20000|ft|km|sp=us|sigfig=2}} by 0926. DOD-sponsored experiments for NUTMEG were Projects 6.3, 6.3a, 6.4, 6.5, 6.6, and 6.11. Projects 6.3 and 6.3a had stations near the burst point on Eneman Island.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=156}}

===Yellowwood===
YELLOWWOOD predicted fallout, surface radiological (radix) exclusion area, and ship positions. YELLOWWOOD was detonated at 1400 on May 26, 1958. YELLOWWOOD was detonated on a barge {{convert|5000|ft|km|sp=us|sigfig=2}} southwest of [[Engebi Island|Enjebi]], and produced a {{convert|330|ktonTNT}} yield range.<ref name=CW_2/> The DOD sponsored 13 experiments for YELLOWWOOD: Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, 6.4, 6.5, 6.6, 6.8, 6.9, 6.11, and 8.1. Instrument stations for Project 2.4 were located on buoys in the lagoon. The remaining projects had more distant stations or were primarily airborne.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|pages=193–195}}

===Magnolia===
Predicted fallout, surface radiological exclusion (radix) area, ship positions, and aircraft participation. MAGNOLIA was detonated at 0600 on May 27, 1958. MAGONLIA was detonated on a barge {{convert|3000|ft|m|sp=us|sigfig=3}} southwest of the center of Runit, and produced a {{convert|57|ktonTNT}} yield range.<ref name=CW_2/> The detonation produced a {{convert|44000|ft|km|sp=us|adj=on|sigfig=3}} cloud that stabilized at {{convert|41000|ft|km|sp=us|sigfig=3}} with its base at {{convert|15000|ft|km|sp=us|sigfig=2}}. The DOD-sponsored experiments for MAGNOLIA were Projects: 3.7, 5.2, and 5.3. Instruments for Project 3.7 were on Boken, Enjebi, and Runit.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=197}}

===Tobacco===
TOBACCO predicted fallout, surface radiological exclusion (radix) area, ship positions, and aircraft participation. TOBACCO was detonated at 1415 on May 30, 1958. TOBACCO was detonated on a barge {{convert|3000|ft|m|sp=us|sigfig=3}} northwest of Enjebi, and produced an {{convert|11.6|ktonTNT}} yield range.<ref name=CW_2/> The detonation produced an {{convert|18000|ft|km|sp=us|adj=on|sigfig=2}} cloud that stabilized at {{convert|16000|ft|km|sp=us|sigfig=2}} by 1430. The DOD-sponsored experiments for TOBACCO were Projects 3.7, 5.1, 5.2, 5.3, and 6.8. The project activity for Project 3.7 was on Boken, Enjebi, and Runit. Project 6.8 simply monitored TOBACCO from stations off Enewetak and [[Parry Island (Pacific)|Parry islands]].<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=199}}

===Sycamore===
SYCAMORE predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. SYCAMORE was detonated at 1500 on May 31, 1958. SYCAMORE was detonated on a barge moored in the BRAVO crater, and produced a {{convert|92|ktonTNT}} yield range.<ref name=CW_2/> DOD-sponsored experiments for SYCAMORE were Projects: 3.7, 5.1, 6.4, 6.5, 6.6, and 6.11. Only Project 6.11 had an instrument site at the [[Bikini Atoll]].<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=160}}

===Maple===
MAPLE predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. MAPLE was detonated on June 11 at 0530 1958. MAPLE was detonated on a barge just south of [[Lomilik]], and produced a {{convert|213|ktonTNT}} yield range.<ref name=CW_2/> The {{convert|40000|ft|km|sp=us|sigfig=3}} cloud produced by the detonation was tracked by radar from Benner. The DOD-sponsored experiments for MAPLE were Projects 5.1, 6.3, and 6.3a. Projects 6.3 and 6.3a shared the same, rather close-in sites on Lomilik.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=162}}

===Aspen===
ASPEN predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. ASPEN was detonated on 15 June 58 at 0530. ASPEN was detonated on a barge in the BRAVO crater of [[Bikini Atoll|Bikini]], {{convert|4000|ft|km|abbr=on|sp=us|sigfig=3}} southwest of Nam. ASPEN produced a {{convert|319|ktonTNT}} yield range.<ref name=CW_2/> The detonation produced a {{convert|48600|ft|km|sp=us|adj=on|sigfig=3}} cloud as measured by radar from Benner. No experiments were sponsored by the DOD for this shot.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=154}}

===Walnut===
WALNUT predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. WALNUT was detonated on June 15, 1958, at 0630, 1 hour after the ASPEN event at Bikini. WALNUT was detonated on a barge {{convert|5000|ft|km}} southwest of Enjebi Island in [[Enewetak Atoll|Enewetak]]. The detonation produced a {{convert|61000|ft|km|sp=us|sigfig=3}} cloud, and produced a {{convert|1.45|MtonTNT}} yield range.<ref name=CW_2/> The DOD-sponsored experiments for WALNUT included Projects 2.4, 2.8, 3.7, 5.1, 5.2, 5.3, and 8.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=154}}

===Linden===
LINDEN predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. LINDEN was detonated on June 18, 1958, at 1500. LINDEN was detonated on a barge {{convert|4000|ft|km|abbr=on|sp=us|sigfig=3}} west of the center of [[Enewetak Atoll|Runit]] Island at Enewetak. The detonation produced a {{convert|20000|ft|km|sp=us|adj=on|sigfig=2}} cloud with a {{convert|7000|ft|km|sp=us|adj=on|sigfig=2}} base, and produced an {{convert|11|ktonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were conducted during LINDEN.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=203}}

===Redwood===
REDWOOD predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. REDWOOD was detonated on June 28, 1958, at 0530. REDWOOD was detonated on a barge south of Lomilik in [[Bikini Atoll|Bikini]]. REDWOOD was followed by the ELDER detonation at Enewetak Atoll one hour later. The detonation cloud base was at {{convert|28000|ft|km|sp=us|adj=off|sigfig=2}} and the top stabilized at {{convert|55000|ft|km|sp=us|sigfig=3}}, and produced a {{convert|412|ktonTNT}} yield range.<ref name=CW_2/> The only DOD-sponsored experiment for REDWOOD was Project 5.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=168}}

===Elder===
ELDER predicted fallout, surface radiological exclusion (radex) areas, ship positions, and aircraft participation. ELDER, detonated on June 28, 1958, at 0630. ELDER was the second of a tandem shot with REDWOOD (detonated an hour earlier on Bikini). ELDER was detonated on a barge {{convert|1|nmi|mi km}} southeast of Enjebi Island in Enewetak. Initial cloud height had been well over {{convert|65000|ft|km|sp=us|sigfig=3}}, and produced an {{convert|880|ktonTNT}} yield range.<ref name=CW_2/> The only DOD-sponsored experiment for ELDER was project 5.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=168}}

===Oak===
OAK predicted fallout, surface radiological exclusion (radex) area, and ship positions. OAK, one of the largest detonations at [[Enewetak Atoll]], and was fired at 0730 on June 29, 1958. OAK was detonated on a barge moored on the reef {{convert|21000|ft|km|sp=us|sigfig=3}} southwest of Bokoluo Island. It was followed at noon by the HICKORY shot at Bikini. The initial height of the cloud was estimated to be {{convert|78000|ft|km|sp=us|adj=off|sigfig=3}}, and produced an {{convert|8.9|MtonTNT}} yield range.<ref name=CW_2/> Two DOD-sponsored experiments were included for OAK: Projects 2.8 and 5.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=205}}

Predicted yield for Oak was {{convert|7.5|MtTNT}}.<ref>{{Cite conference| title = QUARTERLY PROGRESS REPORT TO THE JOINT COMMITTEE ON ATOMIC ENERGY, PART III-WEAPONS, APRIL-JUNE 1958 (DELETED)| accessdate = 2022-11-14| date = 1958-06-30| url = https://www.osti.gov/opennet/detail?osti-id=16092909| page = 5| archive-date = November 14, 2022| archive-url = https://web.archive.org/web/20221114073219/https://www.osti.gov/opennet/detail?osti-id=16092909| url-status = live}}</ref>

===Hickory===
HICKORY predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. HICKORY was detonated on June 29, 1958, at 1200. HICKORY was detonated on a barge off the west end of Enema at Bikini, 4½ hours after the OAK shot at Enewetak Atoll. The detonation cloud rose to {{convert|24200|ft|km|sp=us|adj=off|sigfig=2}} with an estimated {{convert|12000|ft|km|sp=us|adj=on|sigfig=2}} base, and produced a {{convert|14|ktonTNT}} yield range.<ref name=CW_2/> Projects 6.3 and 6.3a were the only DOD-sponsored experiments for HICKORY.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=170}}

===Sequoia===
SEQUOIA predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. SEQUOIA was detonated on July 2, 1958, at 0630. SEQUOIA was detonated on a barge {{convert|2000|ft|m|sp=us|adj=off|sigfig=3}} west-northwest of Runit Island at Enewetak. The cloud stabilized at {{convert|15000|ft|km|sp=us|adj=off|sigfig=3}}, and produced a {{convert|52|ktonTNT}} yield range.<ref name=CW_2/> SEQUIA had no DOD-sponsored experiments.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=209}}

===Cedar===
CEDAR predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. CEDAR was detonated on July 3, 1958, at 0530. CEDAR was detonated on a barge in the BRAVO crater southwest of Nam, {{convert|4000|ft|km|sp=us|sigfig=2}} from the edge of the island at Bikini. The CEDAR detonation produced a {{convert|50000|ft|km|sp=us|adj=on|sigfig=3}} cloud, and produced a {{convert|220|ktonTNT}} yield range.<ref name=CW_2/> The only DOD-sponsored experiment for CEDAR was Project 5.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=172}}

===Dogwood===
DOGWOOD predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. DOGWOOD was detonated on July 6, 1958, at 0630. DOGWOOD was detonated on a barge southwest of Enjebi, {{convert|4000|ft|km|sp=us|sigfig=3}} from the edge of the island at Enewetak. The cloud rose to {{convert|58000|ft|km|sp=us|sigfig=3}}, stabilizing at {{convert|54000|ft|km|sp=us|sigfig=3}} with a {{convert|35000|ft|km|sp=us|adj=on|sigfig=3}} base, and produced a {{convert|397|ktonTNT}} yield range.<ref name=CW_2/> The only DOD-sponsored experiment for DOGWOOD Was Project 5.1.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=211}}

===Poplar===
POPLAR predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. POPLAR was detonated on July 12, 1958, at 1530. POPLAR was detonated on a barge southwest of Nam, at [[Bikini Atoll|Bikini]]. The detonation cloud quickly rose above the tracking radar limits of {{convert|61000|ft|km|sp=us|sigfig=3}}, and the base was established at {{convert|42000|ft|km|sp=us|adj=off|sigfig=3}} at 1540, and produced a {{convert|9.3|MtonTNT}} yield range.<ref name=CW_2/> The only DOD-sponsored experiment for POPLAR was Project 3.7.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=176}}

===Scaevola===
SCAEVOLA predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. Scaevola was detonated on July 14, 1958, at 1600. Scaevola was detonated on a barge west of Runit Island at Enewetak. Its yield was low and the explosion did not destroy the shot barge but only damaged it, producing a {{convert|0|ktonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were scheduled for Scaevola.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=213}}

===Pisonia===
PISONIA predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. PISONIA was detonated on July 18, 1958, at 1100. PISONIA was detonated on a barge {{convert|10000|ft|km|sp=us|adj=off|sigfig=3}} west of Runit Island at [[Enewetak Atoll|Enewetak]]. The cloud rose immediately to {{convert|55000|ft|km|sp=us|adj=off|sigfig=3}}, and produced a {{convert|255|ktonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were scheduled for PISONIA.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=215}}

===Juniper===
JUNIPER predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. JUNIPER, the last nuclear detonation to occur at Bikini, was detonated on July 22, 1958, at 1620. JUNIPER was detonated on a barge {{convert|4000|ft|km|sp=us|adj=off|sigfig=3}} from the west end of Eneman in the Redwing Zuni crater at Bikini. The detonation cloud rose to {{convert|40000|ft|km|sp=us|adj=off|sigfig=3}} with an estimated {{convert|24000|ft|km|sp=us|adj=on|sigfig=3}} base, and produced a {{convert|65|ktonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were scheduled for JUNIPER.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=180}}

===Olive===
OLIVE predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. OLIVE was detonated on July 23, 1958, at 0830. OLIVE was detonated on a barge southwest of Enjebi Island, at Enewetak Atoll. {{convert|4000|ft|km|sp=us|adj=off|sigfig=3}} from the nearest land at Enewetak. The cloud rose to {{convert|50000|ft|km|sp=us|adj=off|sigfig=3}} with an estimated {{convert|15000|ft|km|sp=us|adj=on|sigfig=3}} base, and produced a {{convert|202|ktonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were scheduled for OLIVE.<ref name=CW_2/>{{rp|page=2}}<ref name=CW_3/>{{rp|page=217}}

===Pine===
PINE predicted fallout, surface radiological exclusion (radex) area, ship positions, and aircraft participation. PINE was detonated on July 27, 1958, at 0830. PINE was detonated on a barge southwest of [[Enewetak Atoll|Enjebi]] Island, {{convert|8500|ft|nmi mi km}} from the nearest land, at Enewetak. The cloud rose quickly to {{convert|66000|ft|km|sp=us|adj=off|sigfig=3}} with an estimated {{convert|38000|ft|km|sp=us|adj=on|sigfig=3}} base as measured by radar, and produced a {{convert|2|MtonTNT}} yield range.<ref name=CW_2/> No DOD-sponsored experiments were scheduled for PINE.<ref name=CW_2/>{{rp|page=3}}<ref name=CW_3/>{{rp|page=220}}

== Underwater tests ==
Underwater tests were conducted to assess the damages to Navy boats and materials. The location for these tests was Enewetak due to the uniformity of the sea bottom in the area. This is critical for the tests so that proper moorings of the target ships can be secured on the sea floor. The underwater explosions create a bubble from the expended energy of the blast. This bubble is due to the vaporization of water that directly absorbs the heat of the blast. This bubble may break the surface depending on how much energy is dispersed and the depth of the nuclear device. The bubble displaces large amounts of water that then collapses in on the bubble after all the energy is expended. The water collapsing in on the cavity is called the "radioactive pool" and has the highest concentration of radioactive material.<ref name=CW_3/>{{rp|pages=28–29}}

Many different projects were put in place to test the two underwater blasts. Wave generation, hydrodynamic variables, and energy released were all studied using multiple sensors. These sensors were placed in multiple areas such as target ships and floating balloons. Oceanographic, seismographic and hydrographic surveys were completed after each nuclear blast. A project that used a nuclear blast to clear minefields was studied using the Umbrella blast. One hundred and twenty inert mines were placed at different distances ranging from {{convert|1500|to|8000|ft|m|sp=us}}. These mines were then picked out of the water to study the effects of the blast at each interval.<ref name=CW_3/>{{rp|page=111–149}}

=== Radiation preparations ===
Another reason for underwater tests was to detect radiation contamination of ships after an underwater nuclear explosion. This meant that the contaminated ships required unique "radsafe" preparations so that the data could be quickly accounted for. After the data on the damage and radiation was recorded, the ships needed decontamination work completed before repairs could be completed. The Radiological and Decontamination Unit consisting of 200 enlisted and one officer was created for the task of decontamination.<ref name=CW_3/>{{rp|page=70–86}} After decontamination, the target ships were repaired for use in a second underwater nuclear weapons test. The amount of radiation exposure was debated for the safety of the crews. [[Roentgen (unit)|Roentgen]]s ({{val|1|u=R}} = ca 0,01 [[Gray (unit)|Gy]] in soft tissue) were used to gauge the [[gamma radiation]] that affected the units working on the nuclear tests.

For the underwater test crew, a limit of {{val|5|u=R}} per blast along with {{val|10|u=R}} per operation was referenced as the limit for exposure. These initial limits were rejected and maximum permissible exposure standards (MPE) were solidified by commanders for the crews working on the decontamination unit. Due to the fast recovery of ships, high contamination values were expected by commanders and set the standard to four roentgens per hour (R/hr). An excess of {{val|4|u=R/hr}} was designated off limits of recovery units. Personnel were given special breathing equipment to work in the interior of ships with an R/hr higher than one. High numbers of personnel working the tests were used to keep individuals within the MPE. Times were calculated to keep the total exposure below two roentgens for the personnel working on the ships. A floating decontamination facility was created on board a transport ship for the Wahoo and Umbrella nuclear tests. This allowed important data analysis and an increase in recovery efficiency.<ref name=CW_3/>{{rp|page=70–86}}

=== Wahoo preparation ===

The nuclear explosion was carried out in open ocean outside of Enewetak. This nuclear test codenamed Wahoo was the first underwater test in the Operation Hardtack series. This test could be considered a continuation of the Wigwam nuclear blast (a deep water nuclear test {{convert|500|nmi}} off the coast of San Diego).<ref name=LT_6/> Like its predecessor, the Wahoo shot was a scientific program that studied the effects of an underwater nuclear blast on Navy systems. The nuclear device was positioned {{convert|500|feet}} deep in the Pacific Ocean. This deep water test required precise targeting arrays to be set up around the blast location, which presented unique problems for the arrays as the winds, sea currents and tides needed to be within certain limits for the data to be accurate. Testing arrays were placed at depths of {{convert|400|to|800|fathom|lk=on}} around the nuclear device. The deep water mooring systems needed for the test proved to be difficult to position, leading many analysts to believe the data skewed. The target ships to be used for this program consisted of three destroyers, an active submarine, a submarine mockup used in Wigwam tests, and a merchant marine ship.<ref name=CW_3/>{{rp|page=225}} It was predicted that no air blast or thermal effects would be presented from the underwater blast. The fallout from the blast was also predicted to stay within the target array due to the southwest surface winds.

=== Wahoo blast ===
The test conditions were met on May 16 allowing for the nuclear device to be detonated. Within a second of detonation, a spray dome was created that reached a height of {{convert|840|feet}} after seven seconds. The overall shape of the spray dome resembled a cone with 45 degree sloped sides. Plumes were seen breaking through the spray dome after six seconds in every direction. The vertical plume continued rising until 12 seconds after the blast while the lateral plumes traveled for 20 seconds before collapsing. The diameter of the spray dome was approximately {{convert|3800|feet}} at the 20 second mark.<ref name=CW_3/>{{rp|page=237}} The base surge reached a radius of {{convert|8000|feet}} in the downwind direction after 1.7 seconds. The downwind surge aided by a {{convert|15|knot|mph km/h}} wind reached speeds of {{convert|21|knot|mph km/h}}. This base surge could be seen for three and a half minutes and for longer from the air as it continued to move across the ocean. When the spray dome and base surge had dissipated, a foam patch could be seen spreading from the surface zero water to reach over {{convert|6,000|feet}}.<ref name=CW_3/>{{rp|page=238}} The nuclear blast was calculated to be {{convert|9|ktonTNT}}.  All fallout stayed within the predicted fallout area with a maximum of {{val|0.030|u=R/hr}}. The target ship at {{convert|5,900|yd|nmi mi km}} was directly hit by the shockwave, vibrating the entire ship and shaking it violently. The Moran merchant marine ship moored at {{convert|2346|ft|m|sp=us}} away was immobilized due to shock damage to its main and auxiliary equipment while also suffering minor hull damage. One hour and ten minutes after detonation, a five-gallon water sample was taken directly above the blast location showing {{val|5|u=R/hr}}. The retrieval team entered a {{val|3.8|u=R/hr}} field after an hour and thirty five minutes.

=== Umbrella preparation ===
The second underwater explosion of the Operation Hardtack series was code-named Umbrella. This test was conducted in the lagoon inside Enewetak. This test could be considered a continuation of underwater test Baker, which was conducted in Bikini Lagoon. Explosions in shallow water can create an underwater crater if close enough to the bottom. The target ships from the Wahoo test were towed into the lagoon to be used again for the Umbrella test. The damage from Wahoo was minor in all cases with the exception of the Moran which required extra refurbishing of the hull. These ships had to be washed down and have the measuring equipment replaced before being put into use. The mooring for Umbrella was considerably easier than for Wahoo due to the location and depth of the lagoon. Information gathered from the Wahoo shot directly affected the Umbrella plans with regard to target array placement and decontamination times. The device was placed with a buoy at a depth of {{convert|150|feet}}.<ref name=LT_6/>

=== Umbrella blast ===
[[File:Hardtack Umbrella nuke.jpg|thumb|The Umbrella blast on June 9 with the {{SS|Michael Moran}} in front.]]
June 9 saw the second underwater nuclear test of the Hardtack I series. The detonation occurred at 11:15 AM (local time) with clear skies and a {{convert|15|to|17|knots|mph km/h}} wind from the east-northeast. Within one-tenth of a second, the spray dome had broken through the surface. The overall shape of the spray dome resembled a vertical column with the plumes helping create the shape. Within 20 seconds of detonation, the maximum height of the column reached {{convert|5000|feet}}. The base surge reached a distance around {{convert|10000|feet}} downwind, reaching out approximately {{convert|6000|feet}} in all directions. This base surge could be seen from the air for about 25 minutes and the foam patch over the blast location lasting even longer.<ref name=CW_3/>{{rp|page=248}} The blast yield of the nuclear device was measured to be {{convert|8|ktonTNT}}. The Umbrella blast created a crater {{convert|3000|ft|abbr=on|sp=us}} in diameter and {{convert|20|ft|abbr=on|sp=us}} in depth in the lagoon. The maximum radiation reading was found to be {{val|0.350|u=R/hr}} by an aircraft flying over the blast location. Radiation was reported to be of small portions, and re-entry was granted 30 minutes after detonation. Out of the major target ships, the highest radiation reading was logged at {{val|0.0015|u=R/hr}} of the stern of the ''Moran''. After all scientific data had been gathered from the target ships, they were restored to be seaworthy and towed back to Pearl Harbor. The ''Moran'' was concluded to be unseaworthy due to the blast and was sunk by naval gunfire near Ikuren Island.<ref name=CW_3/>{{rp|page=251}}

The underwater nuclear tests (Wahoo and Umbrella) gathered scientific data that helped the Department of Defense understand the effects of nuclear weapons on Navy ships. Some of the key points found were that underwater nuclear blasts create less fallout due to the absorption of radioactive material in the water and vaporized droplets. Direct gamma radiation was found to be extremely low, but the base surge was found to be highly radioactive as it passed measurement devices. Smaller radiation concentrations followed in waves mimicking the initial base surge. Almost all free-field radiation activity was found to disappear after fifteen minutes allowing for return to normal operations.<ref name=CW_4/>{{rp|page=86}} The impact of shock waves was less than previously expected. The damage from the shockwave was found to be negligible on the destroyers at the ranges tested, but equipment failure from the blast could immobilize the ships. The preliminary tests of explosive tapered charges were proven to simulate the shock waves of a nuclear device according to the data gathered.<ref name=CW_4/>{{rp|page=91}}

==Gallery==
<gallery class="center" widths="220">
File:Hardtack1Juniper.gif|Hardtack I-''Juniper'', 65-kilotons
File:Hardtack1Poplar.gif|Hardtack I-''Poplar'', 9.3-megatons.
File:HardTack1Umbrella.gif|Hardtack I-''Umbrella'', 8-kilotons.
File:Hardtack1Olive.gif|Hardtack I-''Olive'', 202-kilotons.
File:Hardtack1Fig.gif|Hardtack I-''Fig'', 0.02-kilotons.
File:Hardtack1Oak.gif|Hardtack I-''Oak'', 8.9-megatons.
</gallery>
==List of tests==
{| class="wikitable sortable"
 |+ United States' Hardtack I series tests and detonations
 |-
 !style="background:#ffdead;" | Name <ref group=note>The US, France and Great Britain have code-named their test events, while the USSR and China did not, and therefore have only test numbers (with some exceptions – Soviet peaceful explosions were named). Word translations into English in parentheses unless the name is a proper noun. A dash followed by a number indicates a member of a salvo event.  The US also sometimes named the individual explosions in such a salvo test, which results in "name1 – 1(with name2)". If test is canceled or aborted, then the row data like date and location discloses the intended plans, where known.</ref>
 !style="background:#efefef;" | Date time ([[Universal Time|UT]])
 !style="background:#ffdead;" | Local [[Time Zone|time zone]]<ref group=note>To convert the UT time into standard local, add the number of hours in parentheses to the UT time; for local daylight saving time, add one additional hour. If the result is earlier than 00:00, add 24 hours and subtract 1 from the day; if it is 24:00 or later, subtract 24 hours and add 1 to the day. Historical time zone data obtained from the [[tz database|IANA time zone database]].</ref><ref>{{cite web| title=Time Zone Historical Database| publisher=iana.com| url=http://www.ietf.org/timezones/| access-date=March 8, 2014| archive-date=March 11, 2014| archive-url=https://web.archive.org/web/20140311224729/http://www.ietf.org/timezones/| url-status=live}}</ref>
 !style="background:#efefef;" | [[List of nuclear test sites|Location]]<ref group=note>Rough place name and a latitude/longitude reference; for rocket-carried tests, the launch location is specified before the detonation location, if known. Some locations are extremely accurate; others (like airdrops and space blasts) may be quite inaccurate. "~" indicates a likely pro-forma rough location, shared with other tests in that same area.</ref>
 !style="background:#ffdead;" | [[Elevation]] + height <ref group=note>Elevation is the ground level at the point directly below the explosion relative to sea level; height is the additional distance added or subtracted by tower, balloon, shaft, tunnel, air drop or other contrivance. For rocket bursts the ground level is "N/A". In some cases it is not clear if the height is absolute or relative to ground, for example, ''Plumbbob/John''.  No number or units indicates the value is unknown, while "0" means zero. Sorting on this column is by elevation and height added together.</ref>
 !style="background:#efefef;" | Delivery <ref group=note>Atmospheric, airdrop, balloon, gun, cruise missile, rocket, surface, tower, and barge are all disallowed by the [[Partial Nuclear Test Ban Treaty]]. Sealed shaft and tunnel are underground, and remained useful under the PTBT. Intentional cratering tests are borderline; they occurred under the treaty, were sometimes protested, and generally overlooked if the test was declared to be a peaceful use.</ref><br />Purpose <ref group=note>Include weapons development, weapon effects, safety test, transport safety test, war, science, joint verification and industrial/peaceful, which may be further broken down.</ref>
 !style="background:#efefef;" | [[List of nuclear weapons|Device]]<ref group=note>Designations for test items where known, "?" indicates some uncertainty about the preceding value, nicknames for particular devices in quotes. This category of information is often not officially disclosed.</ref>
 !style="background:#ffdead;" | [[Nuclear weapon yield|Yield]]<ref group=note>Estimated energy yield in [[TNT equivalent|tons, kilotons, and megatons]]. A ton of TNT equivalent is defined as 4.184&nbsp;gigajoules (1&nbsp;gigacalorie).</ref>
<!-- !style="background:#efefef;" class="unsortable" | [[Nuclear fallout|Fallout]]<ref group=note>Radioactive emission to the atmosphere aside from prompt neutrons, where known.  The measured species is only iodine-131 if mentioned, otherwise it is all species. No entry means unknown, probably none if underground and "all" if not; otherwise notation for whether measured on the site only or off the site, where known, and the measured amount of radioactivity released.</ref>-->
 !style="background:#ffdead;" class="unsortable" | References<br />Notes
 |-
 ! ''Yucca''{{anchor|Yucca}}
 | {{dts|1958|4|28}} {{UTC with local time link|hour=02|minute=40|seconds=00.3|year=1958|month=04|day=28}}
 | style="text-align:center;" | edst (12&nbsp;hrs)|| Pacific Proving Grounds {{coord|12.617|167.025|name=Yucca|display=inline}}
 | {{convert|26.21|km|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Balloon|Weapon effect}}
 | [[W25 (nuclear warhead)|W-25]]
 |  style="text-align:center;" | {{convert|1.7|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 />[[Anti-ballistic missile|ABM]] development - part of ''Operation Newsreel'' (high-altitude tests). Fired "about {{convert|85|nmi|abbr=on}} northwest of Bikini".
 |-
 ! ''Cactus''{{anchor|Cactus}}
 | {{dts|1958|5|5}} {{UTC with local time link|hour=18|minute=15|seconds=00.1|year=1958|month=05|day=05}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.55255|162.34727|name=Cactus|display=inline}}
 | {{convert|1|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Dry surface|Weapons development}}
 | [[B43 nuclear bomb|Mk-43]] primary
 | style="text-align:center;" | {{convert|18|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 /> LASL test of a MK-43 primary in a thermonuclear system mockup.  Similar to ''Elder''. {{convert|596|ft|abbr=on}} crater southwest of the ''Redwing Lacrosse'' crater; crater later became the ''Cactus Dome''.
 |-
 ! ''Fir''{{anchor|Fir}}
 | {{dts|1958|5|11}} {{UTC with local time link|hour=17|minute=50|seconds=00.1|year=1958|month=05|day=11}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Namu (Charlie), Bikini Atoll {{coord|11.6908|165.2733|name=Fir|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 |
 | style="text-align:center;" | {{convert|1.4|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Clean 2-stage TN device, only {{convert|90|ktonTNT}} fission, {{Percentage | 934 | 1000 | sigfig = 3 }} fusion yield.
 |-
 ! ''Butternut''{{anchor|Butternut}}
 | {{dts|1958|5|11}} {{UTC with local time link|hour=18|minute=15|seconds=00.1|year=1958|month=05|day=05}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.53859|162.34367|name=Butternut|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B46 nuclear bomb|TX-46]] primary ?
 | style="text-align:center;" | {{convert|81|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> TX-46 primary test, similar to ''Oak'' and ''Yellowwood''.
 |-
 ! ''Koa''{{anchor|Koa}}
 | {{dts|1958|5|12}} {{UTC with local time link|hour=18|minute=30|seconds=00.1|year=1958|month=05|day=12}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Teiter (Gene), Enewetak Atoll {{coord|11.66997|162.19847|name=Koa|display=inline}}
 | {{convert|0.81|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Dry surface|Weapons development}}
 | [[XW-35]]
 | style="text-align:center;" | {{convert|1.4|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> XW-35 [[Intercontinental ballistic missile|ICBM]] warhead test.
 |-
 ! ''Wahoo''{{anchor|Wahoo}}
 | {{dts|1958|5|16}} {{UTC with local time link|hour=01|minute=30|seconds=00.5|year=1958|month=05|day=16}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Pokon (Irvin), Enewetak Atoll {{coord|11.32646|162.16309|name=Wahoo|display=inline}}
 | {{convert|-150|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|[[underwater explosion|underwater]]|Weapon effect}}
 | [[Mark 7 nuclear bomb|Mk-7]]
 | style="text-align:center;" | {{convert|9|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Mk-7 deep [[underwater explosion]] effects, water depth {{convert|3200|ft|abbr=on}}.
 |-
 ! ''Holly''{{anchor|Holly}}
 | {{dts|1958|5|20}} {{UTC with local time link|hour=18|minute=30|seconds=00.1|year=1958|month=05|day=20}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54029|162.35039|name=Holly|display=inline}}
 | {{convert|4|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W31|XW-31Y3]]
 | style="text-align:center;" | {{convert|5.9|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> XW-31Y3 proof test.
 |-
 ! ''Nutmeg''{{anchor|Nutmeg}}
 | {{dts|1958|5|21}} {{UTC with local time link|hour=21|minute=20|seconds=00.2|year=1958|month=05|day=21}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Eninmen (Tare), Bikini Atoll {{coord|11.50355|165.3722|name=Nutmeg|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | early [[W47|XW-47]] ?
 | style="text-align:center;" | {{convert|25.1|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> 2 stage thermonuclear device, possible W47.
 |-
 ! ''Yellowwood''{{anchor|Yellowwood}}
 | {{dts|1958|5|26}} {{UTC with local time link|hour=02|minute=00|seconds=00.1|year=1958|month=05|day=26}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.65751|162.22168|name=Yellowwood|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B46 nuclear bomb|TX-46]], became W-53
 | style="text-align:center;" | {{convert|330|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 /> LASL developmental test of a "clean" TX-46 warhead design. Fizzled, low burn in secondary. Retry in ''Oak''.
 |-
 ! ''Magnolia''{{anchor|Magnolia}}
 | {{dts|1958|5|26}} {{UTC with local time link|hour=18|minute=00|seconds=00.1|year=1958|month=05|day=26}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.53932|162.34841|name=Magnolia|display=inline}}
 | {{convert|4|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | "Cougar"
 | style="text-align:center;" | {{convert|57|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Proof test.
 |-
 ! ''Tobacco''{{anchor|Tobacco}}
 | {{dts|1958|5|30}} {{UTC with local time link|hour=02|minute=15|seconds=00.2|year=1958|month=05|day=30}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.66056|162.22663|name=Tobacco|display=inline}}
 | {{convert|2.7|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W50 (nuclear warhead)|XW-50]]
 | style="text-align:center;" | {{convert|11.6|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Exploratory shot, XW-50 Nike-Zeus prototype, 2nd stage failed to ignite.
 |-
 ! ''Sycamore''{{anchor|Sycamore}}
 | {{dts|1958|5|31}} {{UTC with local time link|hour=03|minute=00|seconds=00.1|year=1958|month=05|day=31}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Namu (Charlie), Bikini Atoll {{coord|11.69722|165.27486|name=Sycamore|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B41 nuclear bomb|TX-41]]
 | style="text-align:center;" | {{convert|92|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 />"Clean" TX-41 fizzle; predicted yield {{convert|5|MtonTNT|abbr=on}} total, {{convert|200|ktonTNT|abbr=on}} fission; low level burning in 2nd stage; similar to ''Poplar'' and ''Pine''.
 |-
 ! ''Rose''{{anchor|Rose}}
 | {{dts|1958|6|2}} {{UTC with local time link|hour=18|minute=45|seconds=00.1|year=1958|month=06|day=02}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.53926|162.34593|name=Rose|display=inline}}
 | {{convert|4.5|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W49|XW-49]] ? Primary
 | style="text-align:center;" | {{convert|15|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Exploratory shot, possible XW-49, 80&nbsp;kt fusion expected, 2nd stage failed to ignite.
 |-
 ! ''Umbrella''{{anchor|Umbrella}}
 | {{dts|1958|6|8}} {{UTC with local time link|hour=23|minute=15|seconds=00.2|year=1958|month=06|day=08}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Pokon (Irvin), Enewetak Atoll {{coord|11.37498|162.19399|name=Umbrella|display=inline}}
 | {{convert|-50|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|[[underwater explosion|underwater]]|Weapon effect}}
 | [[Mark 7 nuclear bomb|Mk-7]]
 | style="text-align:center;" | {{convert|8|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 /> Shallow [[underwater explosion]] on lagoon bottom at {{convert|150|ft|abbr=on}}. Crater {{convert|915|x|6|m|abbr=on}}.
 |-
 ! ''Maple''{{anchor|Maple}}
 | {{dts|1958|6|10}} {{UTC with local time link|hour=17|minute=30|seconds=00.1|year=1958|month=06|day=10}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Yurochi aka Irioj (Dog), Bikini Atoll {{coord|11.6915|165.41582|name=Maple|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 |
 | style="text-align:center;" | {{convert|213|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 />"Dirty" 2-stage test, predicted to be {{Percentage | 89 | 100 }} fission.
 |-
 ! ''Aspen''{{anchor|Aspen}}
 | {{dts|1958|6|14}} {{UTC with local time link|hour=17|minute=30|seconds=00.1|year=1958|month=06|day=14}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Namu (Charlie), Bikini Atoll {{coord|11.6908|165.2733|name=Aspen|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W47|XW-47]] ?
 | style="text-align:center;" | {{convert|319|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Possible XW-47 prototype, 2 stage.
 |-
 ! ''Walnut''{{anchor|Walnut}}
 | {{dts|1958|6|14}} {{UTC with local time link|hour=18|minute=30|seconds=00.1|year=1958|month=06|day=14}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.65751|162.22168|name=Walnut|display=inline}}
 | {{convert|2|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 |
 | style="text-align:center;" | {{convert|1.5|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Thermonuclear prototype development test.
 |-
 ! ''Linden''{{anchor|Linden}}
 | {{dts|1958|6|18}} {{UTC with local time link|hour=03|minute=00|seconds=00.1|year=1958|month=06|day=18}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54061|162.35106|name=Linden|display=inline}}
 | {{convert|2.5|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W50 (nuclear warhead)|XW-50]] primary ?
 | style="text-align:center;" | {{convert|11|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Possible XW-50 primary.
 |-
 ! ''Redwood''{{anchor|Redwood}}
 | {{dts|1958|6|27}} {{UTC with local time link|hour=17|minute=30|seconds=00.1|year=1958|month=06|day=27}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Yurochi aka Irioj (Dog), Bikini Atoll {{coord|11.6915|165.41582|name=Redwood|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W47|XW-47]] ?
 | style="text-align:center;" | {{convert|412|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Possible XW-47 prototype, 2-stage, {{convert|250|ktonTNT|abbr=on}} fission yield expected; similar to ''Aspen, Nutmeg, Dogwood'' devices.
 |-
 ! ''Elder''{{anchor|Elder}}
 | {{dts|1958|6|27}} {{UTC with local time link|hour=18|minute=30|seconds=00.1|year=1958|month=06|day=27}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.66056|162.22663|name=Elder|display=inline}}
 | {{convert|2.7|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B43 nuclear bomb|TX-43]]
 | style="text-align:center;" | {{convert|880|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> TX-43 laydown bomb test, {{Percentage | 50 | 100 }} fission yield expected, similar to ''Cactus''.
 |-
 ! ''Oak''{{anchor|Oak}}
 | {{dts|1958|6|28}} {{UTC with local time link|hour=19|minute=30|seconds=00.1|year=1958|month=06|day=28}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Bogallua (Alice), Enewetak Atoll {{coord|11.60309|162.10259|name=Oak|display=inline}}
 | {{convert|1.8|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B46 nuclear bomb|TX-46/53]]
 | style="text-align:center;" | {{convert|8.9|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 /> Prototype test of the LASL designed TX-46 system. Similar to ''Butternut'' and ''Yellowwood''. Crater {{convert|1750|x|80|m|abbr=on}}.
 |-
 ! ''Hickory''{{anchor|Hickory}}
 | {{dts|1958|6|29}} {{UTC with local time link|hour=00|minute=00|seconds=00.9|year=1958|month=06|day=29}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Eninmen (Tare), Bikini Atoll {{coord|11.4961|162.3708|name=Hickory|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W47|XW-47]] primary ?
 | style="text-align:center;" | {{convert|14|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Possible XW-47 primary test, similar to ''Hardtack II Neptune'' and ''Titania''.
 |-
 ! ''Sequoia''{{anchor|Sequoia}}
 | {{dts|1958|7|1}} {{UTC with local time link|hour=18|minute=30|seconds=00.1|year=1958|month=07|day=01}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54061|162.35106|name=Sequoia|display=inline}}
 | {{convert|2|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W50 (nuclear warhead)|XW-50]] primary ?
 | style="text-align:center;" | {{convert|5.2|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Similar to ''Hardtack II Otero'', test of ''Hardtack I Pisonia'' primary.
 |-
 ! ''Cedar''{{anchor|Cedar}}
 | {{dts|1958|7|2}} {{UTC with local time link|hour=17|minute=30|seconds=00.1|year=1958|month=07|day=02}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Namu (Charlie), Bikini Atoll {{coord|11.69722|165.27486|name=Cedar|display=inline}}
 | {{convert|3.4|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 |
 | style="text-align:center;" | {{convert|220|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> 2-stage "clean" thermonuclear device, predicted fission yield {{convert|30|ktonTNT|abbr=on}}.
 |-
 ! ''Dogwood''{{anchor|Dogwood}}
 | {{dts|1958|7|5}} {{UTC with local time link|hour=18|minute=30|seconds=00.2|year=1958|month=07|day=05}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.66056|162.22663|name=Dogwood|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W47|XW-47]] ? Piccolo
 | style="text-align:center;" | {{convert|397|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Similar to ''Redwood, Aspen, Nutmeg''; possible XW-47 prototype, Piccolo 2nd stage.
 |-
 ! ''Poplar''{{anchor|Poplar}}
 | {{dts|1958|7|12}} {{UTC with local time link|hour=03|minute=30|seconds=00.1|year=1958|month=07|day=12}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Namu (Charlie), Bikini Atoll {{coord|11.69704|165.26708|name=Poplar|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B41 nuclear bomb|TX-41]]
 | style="text-align:center;" | {{convert|9.3|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> TX-41 "clean" 2-stage variant; similar to ''Pine'' and ''Sycamore''; largest of ''Hardtack I'', and 5th largest U.S. test ever.
 |-
 ! ''Scaevola''{{anchor|Scaevola}}
 | {{dts|1958|7|14}} {{UTC with local time link|hour=04|minute=00|year=1958|month=07|day=14}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54662|162.35199|name=Scaevola|display=inline}}
 | {{convert|6|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Safety experiment}}
 | [[W34 (nuclear warhead)|XW-34]]
 | style="text-align:center;" | {{convert|0|tonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /><ref name=LT_44 /> XW-34 1-point safety test, successful.
 |-
 ! ''Pisonia''{{anchor|Pisonia}}
 | {{dts|1958|7|17}} {{UTC with local time link|hour=23|minute=00|year=1958|month=07|day=17}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.55|162.31|name=Pisonia|display=inline}}
 | {{convert|2|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W50 (nuclear warhead)|XW-50]] ? TN, sequoiah pr
 | style="text-align:center;" | {{convert|255|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /><ref name=LT_44 /> Probable prototype XW-50 thermonuclear design, modified ''Tobacco'' device, used ''Sequoia'' primary.
 |-
 ! ''Juniper''{{anchor|Juniper}}
 | {{dts|1958|7|22}} {{UTC with local time link|hour=04|minute=20|seconds=00.1|year=1958|month=07|day=22}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Eninmen (Tare), Bikini Atoll {{coord|11.50355|165.3722|name=Juniper|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[W47|XW-47]]
 | style="text-align:center;" | {{convert|65|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_148 /><ref name=LT_24 />"Most radical UCRL shot", "entirely new concept", last Bikini atmospheric shot, probable XW-47 candidate.
 |-
 ! ''Olive''{{anchor|Olive}}
 | {{dts|1958|7|22}} {{UTC with local time link|hour=20|minute=30|seconds=00.2|year=1958|month=07|day=22}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.66056|162.22663|name=Olive|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 |
 | style="text-align:center;" | {{convert|202|ktonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> Concept feasibility test, 2-stage thermonuclear device, established high yield/light weight; weight {{convert|100|kg|abbr=on}}  (yield/weight ratio {{convert|2|ktonTNT/kg|abbr=on}} 2&nbsp;kt/kg).
 |-
 ! ''Pine''{{anchor|Pine}}
 | {{dts|1958|7|26}} {{UTC with local time link|hour=20|minute=30|seconds=00.2|year=1958|month=07|day=26}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Enjebi (Janet), Enewetak Atoll {{coord|11.6513|162.21414|name=Pine|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Barge|Weapons development}}
 | [[B41 nuclear bomb|Mk-41]]
 | style="text-align:center;" | {{convert|2|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /> TX-41 "clean" 3-stage variant; similar to ''Poplar'' and ''Sycamore''.
 |-
 ! ''Piñon''<br>''(canceled)''{{anchor|Piñon}}
 | {{dts|1958|8}}
 | style="text-align:center;" | edst (12&nbsp;hrs)|| Pacific Proving Grounds {{coord|12|162|name=Piñon|display=inline}}
 | {{convert|3|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Air drop|Weapon effect}}
 |
 | style="text-align:center;" | {{sort|000000000|unknown}}
 | A proposed international demonstration of a clean thermonuke.  Cancelled by President [[Dwight D. Eisenhower|Eisenhower]] in the runup to the 1958 test moratorium.
 |-
 ! ''[[Hardtack Teak|Teak]]''{{anchor|Teak}}
 | {{dts|1958|8|1}} {{UTC with local time link|hour=10|minute=50|seconds=05.6|year=1958|month=08|day=01}}
 | style="text-align:center;" | jamt (–11&nbsp;hrs)<br />{{small|Believed in use during ''Dominic, Fishbowl, HT I''.<ref name=LT_215 />{{rp|page=4}} }}
 | {{ubl|Launch from Johnston Island, Johnston Atoll {{coord|16.73365|-169.52534|name=Launch_Teak|display=inline}}, elv: {{convert|3|+|0|m|abbr=on}}|Detonation over Johnston Island, Johnston Atoll {{coord|16.7439|-169.5333|name=Teak|display=inline}}}}
 | {{convert|81.3|km|abbr=on|disp=br()|sortable=on}}
 | {{ubl|High-alt rocket {{convert|30|-|80|km|ft|disp=br()}}|Weapon effect}}
 | [[W39 (nuclear warhead)|W-39]]
 | style="text-align:center;" | {{convert|3.8|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 />[[Anti-ballistic missile|ABM]] effects test. Miscalculation resulted in detonation directly above launch site.  Part of Operation Newsreel (high-altitude tests), carried on a Redstone rocket.
 |-
 ! ''Quince''{{anchor|Quince}}
 | {{dts|1958|8|6}} {{UTC with local time link|hour=02|minute=15|year=1958|month=08|day=06}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54828|162.35079|name=Quince|display=inline}}
 | {{convert|1|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Dry surface|Weapons development}}
 | [[XW-51]] ?
 | style="text-align:center;" | {{sort|000000000|no yield}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 /><ref name=LT_44 /> Probable XW-51 test, fizzle.
 |-
 ! ''Orange''{{anchor|Orange}}
 | {{dts|1958|8|12}} {{UTC with local time link|hour=10|minute=30|seconds=08.6|year=1958|month=08|day=12}}
 | style="text-align:center;" | jamt (–11&nbsp;hrs)<br />{{small|Believed in use during ''Dominic, Fishbowl, HT I''.<ref name=LT_215 />{{rp|page=page=4}}}} |
 | {{ubl|Launch from Johnston Island, Johnston Atoll {{coord|16.73365|-169.52534|name=Launch_Orange|display=inline}}, elv: {{convert|3|+|0|m|abbr=on}}|Detonation over Johnston Island, Johnston Atoll {{coord|16.3583|-169.5356|name=Orange|display=inline}}}}
 | {{convert|45.5|km|abbr=on|disp=br()|sortable=on}}
 | {{ubl|High-alt rocket {{convert|30|-|80|km|ft|disp=br()}}|Weapon effect}}
 | [[W39 (nuclear warhead)|W-39]]
 | style="text-align:center;" | {{convert|3.8|MtonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_206 /><ref name=LT_24 />[[Anti-ballistic missile|ABM]] effects test, W-39 warhead, part of Operation Newsreel (high-altitude tests), carried on a Redstone rocket.
 |-
 ! ''Fig''{{anchor|Fig}}
 | {{dts|1958|8|18}} {{UTC with local time link|hour=04|minute=00|year=1958|month=08|day=18}}
 | style="text-align:center;" | MHT (11&nbsp;hrs)|| Runit (Yvonne), Enewetak Atoll {{coord|11.54955|162.34879|name=Fig|display=inline}}
 | {{convert|0.5|m|abbr=on|disp=br()|sortable=on}}
 | {{ubl|Dry surface|Weapons development}}
 | [[XW-51]] ?
 | style="text-align:center;" | {{convert|20|tonTNT|abbr=on|lk=on|disp=br()|sortable=on}}
 | <ref name=LT_1 /><ref name=LT_6 /><ref name=LT_24 /><ref name=LT_44 /> Probable XW-51 test, similar to ''Quince'', successful, last atmospheric shot at Enewetak.
 |}

{{Reflist|group=note}}

==References==
{{Reflist|25em|refs=

<ref name=LT_1>{{cite tech report | last1=Yang | first1=Xiaoping | first2=Robert| last2=North| first3=Carl| last3=Romney| title=CMR Nuclear Explosion Database (Revision 3) | number= CMR Technical Report, CMR-00/16 | institution= SMDC Monitoring Research | date=August 2000 }}</ref>

<ref name=LT_24>{{cite book| last= Hansen| first= Chuck | author-link = Chuck Hansen| year=1995| title= The Swords of Armageddon : U.S. Nuclear Weapons Development since 1945 | volume=8| publisher= Chukelea Publications| location=Sunnyvale, CA| isbn=978-0-9791915-1-0 | oclc = 231585284}}</ref>

<ref name=LT_206>{{cite tech report | title = Operation HARDTACK, Technical Summary of Military Effects Programs 1 - 9, Sanitized Version | url= https://www.scribd.com/doc/30470418/Operation-HARDTACK-Technical-Summary-of-Military-Effects-Programs-1-9-Sanitized-Version | number = ITR-1660-SAN |institution = [[Defense Threat Reduction Agency|Defense Atomic Support Agency]] | date=1959-09-23 | archive-url = https://web.archive.org/web/20210208150300/https://www.scribd.com/doc/30470418/Operation-HARDTACK-Technical-Summary-of-Military-Effects-Programs-1-9-Sanitized-Version | archive-date = 2021-02-08 | url-status = live | access-date = 2021-02-08 | df = dmy-all }}</ref>

<ref name=LT_6>{{citation| publisher=Department of Energy, Nevada Operations Office| date=December 1, 2000| title=United States Nuclear Tests: July 1945 through September 1992| type=DOE/NV-209 REV15| location=Las Vegas, NV| url=http://www.oregonstatehospital.net/d/otherfiles/DOENV_209_REV15.pdf| access-date=April 19, 2016| archive-date=December 27, 2014| archive-url=https://web.archive.org/web/20141227104754/http://www.oregonstatehospital.net/d/otherfiles/DOENV_209_REV15.pdf| url-status=live}}</ref>

<ref name=LT_148>{{cite web |url = http://www.nuclearweaponarchive.org/Usa/Tests | title =  Gallery of U.S. Nuclear Tests | last = Sublette | first = Carey | date = 2021-08-06 | website = Nuclear Weapon Archive | access-date = 2021-02-08 | url-status = live | archive-url = https://web.archive.org/web/20210205021306/http://www.nuclearweaponarchive.org/Usa/Tests/ | archive-date = 2021-02-05 | df = dmy-all }}</ref>

<ref name=LT_44>{{citation| last1=Norris| first1=Robert Standish| first2=Thomas B.| last2=Cochran| date=February 1, 1994| title=United States nuclear tests, July 1945 to 31 December 1992 (NWD 94-1)| journal=Nuclear Weapons Databook Working Paper| publisher=Natural Resources Defense Council| location=Washington, DC| url=http://docs.nrdc.org/nuclear/files/nuc_02019401a_121.pdf| access-date=October 26, 2013| url-status=dead| archive-url=https://web.archive.org/web/20131029194805/http://docs.nrdc.org/nuclear/files/nuc_02019401a_121.pdf| archive-date=October 29, 2013}}</ref>

<ref name=LT_215>{{citation|last=Hoerlin| first=Herman| title=United States High-Altitude Test Experiences: A Review Emphasizing the Impact on the Environment| series=LA (Series) (Los Alamos, N.M.)6405| type=LA-6405| publisher=Los Alamos Scientific Laboratory| date=October 1976| hdl=2027/mdp.39015086460626}}  Reference for time zone at Johnston Island 1958-1962.</ref>

<ref name=CW_1>{{citation| publisher=United States of America Department of Energy| date=September 1, 2006| title=Battlefield of the Cold War: The Nevada Test Site Volume I, ''Atmospheric Nuclear Weapons Testing, 1951-1963''| type=DOE/MA-0003| location=Washington, D.C.| url=http://energy.gov/sites/prod/files/DOENTSAtmospheric.pdf| access-date=April 19, 2016| archive-date=September 9, 2015| archive-url=https://web.archive.org/web/20150909181750/http://energy.gov/sites/prod/files/DOENTSAtmospheric.pdf| url-status=live}}</ref>

<ref name=CW_2>{{citation| publisher=Defense Threat Reduction Agency| date=May 1, 2015| title=Operation Hardtack I Fact Sheet| location=Fort Belvoir, VA| url=http://www.dtra.mil/Portals/61/Documents/NTPR/1-Fact_Sheets/20_HARDTACK_I.pdf| access-date=April 19, 2016| archive-date=February 29, 2020| archive-url=https://web.archive.org/web/20200229185631/https://www.dtra.mil/Portals/61/Documents/NTPR/1-Fact_Sheets/20_HARDTACK_I.pdf| url-status=dead}}</ref>

<ref name=CW_3>{{citation| publisher=United States of America Department of Defense| date=1958| title=Operation Hardtack I| type=DNA6038F, ADA136819| url=https://www.dtra.mil/Portals/61/Documents/NTPR/2-Hist_Rpt_Atm/1958_DNA_6038F.pdf| access-date=April 19, 2016| archive-date=October 19, 2016| archive-url=https://web.archive.org/web/20161019013721/http://www.dtra.mil/Portals/61/Documents/NTPR/2-Hist_Rpt_Atm/1958_DNA_6038F.pdf| url-status=live}}</ref>

<ref name=CW_4>{{citation|date=September 23, 1959|title=Operation Hardtack Preliminary Report|type=ITR-1660-(SAN), ADA369152|url=https://www.scribd.com/doc/292806893/ITR-1660-Ada369152-HARDTACK-Nuclear-Weapons-Tests-Military-Effects-Studies|access-date=April 20, 2016|archive-date=April 27, 2016|archive-url=https://web.archive.org/web/20160427081840/https://www.scribd.com/doc/292806893/ITR-1660-Ada369152-HARDTACK-Nuclear-Weapons-Tests-Military-Effects-Studies|url-status=live}}</ref>

}}

==External links==
{{Commons category|Operation Hardtack I}}
* {{Internet Archive short film|id=OperationHARDTACK_BasicEffectsStructuresandMateriel1958|name=Operation HARDTACK Military Effects Studies Part I: Basic Effects Structures and Materiel (1958)}}
* {{Internet Archive short film|id=OperationHARDTACK_UnderwaterTests1958|name=Operation HARDTACK Military Effects Studies Part II: Underwater Tests (1958)}}
* {{Internet Archive short film|id=OperationHARDTACK_HighAltitudeTests1958|name=Operation HARDTACK Military Effects Studies Part III: High Altitude Tests (1958)}}
* {{Internet Archive short film|id=OperationHardtackMilitaryEffectsStudiesPartIv-Sub-kilotonEffects|name=Operation HARDTACK Military Effects Studies: Part IV - Sub-kiloton effects }}
* Details of the [http://stratocat.com.ar/stratopedia/11.htm YUCCA balloon-borne nuclear detonation] published at Stratopedia, the balloon encyclopedia

{{US Nuclear Tests}}
{{Authority control}}

[[Category:Explosions in 1958]]
[[Category:Nuclear testing at Bikini Atoll|Hardtack I]]
[[Category:Enewetak Atoll nuclear explosive tests|Hardtack I]]
[[Category:1958 in military history]]
[[Category:1958 in the environment]]
[[Category:1950s in the Marshall Islands]]
[[Category:1958 in the Trust Territory of the Pacific Islands]]