Seaslug (missile)

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Seaslug on display at Wickenby Aerodrome, Lincolnshire, UK

Seaslug was a first-generation surface-to-air missile developed by Armstrong Whitworth (later part of the Hawker Siddeley group) for use by the Royal Navy.<ref>Template:Cite web</ref> Its origins date back to the 1943 LOPGAP project.<ref>Template:Cite web</ref> The missile entered operational service in 1961 and remained in use until the early 1980s, including during the 1982 Falklands War.<ref>Template:Cite web</ref>

Designed to engage high-altitude targets such as reconnaissance aircraft or bombers before they could launch stand-off weapons, Seaslug was fitted only to the eight County-class destroyers, which were purpose-built around the system.<ref>Template:Cite web</ref> The missile was fired in combat at an airborne target on a single occasion, by Template:HMS during the Falklands War, but failed to hit its target,<ref>Template:Cite web</ref> although it was later used against surface targets.<ref>Template:Cite web</ref>

Seaslug's medium-range role was initially intended to be replaced by the long-range Blue Envoy missile. However, Blue Envoy was cancelled in favour of a new medium-range system, Sea Dart. Sea Dart entered service in 1973 aboard the Type 82 destroyer Template:HMS and gradually replaced Seaslug as the Template:Sclass2s were withdrawn from service during the 1980s.<ref>Template:Cite web</ref>

Development

Initial concept

In 1943, the German Luftwaffe began the use of anti-shipping missiles and guided bombs in the Mediterranean Sea during Allied operations against Italy. These weapons were released outside of anti-aircraft gun range, which meant that naval operations lacking complete air superiority would be open to attack with no effective response from the ships.<ref name="Friedman2012">Template:Cite book</ref> A solution for long-range anti-aircraft was required. On 16 March 1944 the first meeting of the "Guided Anti-Aircraft Projectile Committee", was held.Template:Sfn

The Admiralty Signals Establishment (ASE), in charge of the Navy's radar development, was working on new radars featuring radar lock-on that allowed them to accurately track aircraft at long range. This was part of the LRS.1 fire-control system that allowed large dual-purpose guns to attack bombers at long range.Template:Sfn A contemporary British Army project at Cossors, Brakemine, was working on a system to allow a missile to keep itself centred within a radar beam, a concept known today as beam riding. The Navy decided to combine the two concepts, using the LRS.1's Type 901 radar with a new missile that differed from Brakemine primarily in requiring longer range and being more robust for shipborne use.<ref name="Friedman2012p197">Template:Cite book</ref>

In December 1944, GAP put out a Naval Staff Target for a new anti-aircraft weapon,Template:Sfn capable of attacking targets at altitudes up to Template:Convert and speeds of up to Template:Convert.Template:Sfn This project was briefly known as LOPGAP, short for "Liquid Oxygen and Petrol Guided Anti-aircraft Projectile",Template:Sfn but soon moved from petrol to methanol which made the "LOP" inaccurate.Template:Sfn

LOPGAP

The Fairey Aviation Company at this time was working on a missile project for the Ministry of Supply, Stooge. Stooge was more like an armed drone aircraft than a missile. It was flown to a location in front of the target and then cruised toward it until its warhead was triggered by the operator. It was designed primarily to defeat kamikaze attacks at short range. Its low speed and manual guidance meant it was not useful for interceptions outside the immediate area of the ship, and thus did not meet the need for a longer-ranged missile capable of dealing with stand-off weapons.Template:Sfn

Accordingly, Fairey was ordered to stop work on Stooge in favour of LOPGAP.Template:Efn-lr Development was slowed by the Air Ministry who were opposed to the project as it might take resources away from jet fighter productionTemplate:Efn-lr and a lack of urgency on the part of both the Admiralty and Ministry of Supply.Template:Sfn

A March 1945 report called for the first test launches of LOPGAP from converted QF 3.7-inch air-aircraft gun mounts within two months. The same mounts had also been used, with different modifications, for Stooge and Brakemine. They predicted the final system would be about Template:Convert long and a twin-launcher would take up about the same room as a twin 5.25-inch gun turret. An April Staff Target called for the system to be able to engage an aircraft flying at Template:Convert at altitudes up to Template:Convert with a maximum weight of Template:Convert.<ref name="Friedman2012p179">Template:Cite book</ref>

Move to RAE

In 1945 a new Guided Projectiles Establishment was set up under the Controller of Supplies (Air) and in 1946 development of all ongoing missile projects moved to the Royal Aircraft Establishment's (RAE) new Controlled Weapons Department, soon to become the Guided Weapons Department.Template:Sfn They began considering the beam riding concept in partnership with the Telecommunications Research Establishment (TRE), the deliberately oddly-named department of the Air Ministry responsible for radar development. Over the next year, first Brakemine and then Stooge were moved to the RAE.Template:Sfn

In a January 1947 Navy review, the program was given the name Seaslug. This called for a significantly larger weapon than initially envisioned, capable of single-stage vertical launch, a warhead (and guidance) of Template:Convert and an all-up weight of Template:Convert.Template:Sfn Development continued as before but was significantly hampered by the post-war exodus of engineering talent.Template:Sfn Shortly after the new definition was produced, this project also moved to the RAE. Efforts by the Navy to change the name from Seaslug to the more ominous-sounding "Triumph" failed.Template:Sfn

Development slowed, and in July 1947 the Admiralty approached Henry Tizard to argue for a more "virile leadership" of the program. Tizard called a meeting of the Defence Research Policy Committee (DRPC) and started a process of pushing through four key missile programs that were intended to enter service in 1957, Seaslug, a longer ranged Army/Air Force surface-to-air missile known as Red Heathen, the Blue Boar television guided glide bomb, and the Red Hawk air-to-air missile.Template:Sfn

In March 1948 a new report from the DRPC noted there was not enough manpower for all four projects, and put Seaslug at the bottom of the priority list, claiming air attack would be less likely than submarine in the event of war. They suggested the much longer ranged Red Heathen was more important in the short term. The Admiralty was of another opinion on the matter and argued against the change in priority.Template:Sfn

The Navy found an unlikely ally in the Army, who were concerned that Red Heathen was too difficult to move to in a single step and suggested that Seaslug might be the basis for a more immediate medium-range weapon that could be used both on land and sea. The DPRC also began to have concerns about accurately guiding Red Heathen at its desired Template:Convert maximum range. In September 1948 they agreed to develop Seaslug "as a matter of insurance", before further upgrading it in 1949 to "top priority".Template:Sfn As a result of these changes, the program was seen as having two stages, Stage 1 would deliver missiles in the mid-1950s with roughly Template:Convert range with capability mostly against subsonic targets, and a Stage 2 of the early 1960s would have a greatly extended range on the order of Template:Convert and able to attack supersonic aircraft.Template:Sfn

Experimental systems

Two test systems emerged from this centralization. The CTV.1 was a small unpowered Brakemine-like system devoted to the development of the guidance systems, launched using three RP-3 rocket motors and controlled through the coast phase. A series of CTV designs followed, providing ever-increasing amounts of telemetry for the guidance and control systems work.Template:Sfn GAP became a purely research-oriented system, RTV.1 (rocket test vehicle), as opposed to a prototype missile design, and was used primarily as a platform for testing the rocket motors.Template:SfnTemplate:Sfn The GAP/RTV.1 efforts would be directed at the Stage 1 design, which would essentially be the Seaslug requirement.

The relatively small CTV could safely be launched at the Larkhill Range, part of the Royal School of Artillery. It was equipped with a parachute that allowed it to be recovered. This was not possible for the much longer-ranged RTV, which was fired from RAF Aberporth out over Cardigan Bay in Wales. The desire to reclaim the RTVs as well led to the opening of a parallel launch facility at the RAAF Woomera Range Complex and a program that led development of supersonic parachutes.Template:Sfn

As RTV testing continued, the decision was made to build a larger version, RTV.2, which would be more typical of a production missile. During early testing, the design was further modified and renamed GPV, for General Purpose Test Vehicle. Several liquid rocket motors were tested as part of this program. Early tests demonstrated shifts in the center of gravity that required active damping, which in turn led to the lengthening of the overall fuselage to become the "long round". This version used forward-mounted boosters, which were mounted so their exhaust was just in front of the mid-mounted wings.Template:Sfn

Project 502

As experimental work progressed, the Ministry of Supply began forming an industry team to build production systems. In 1949 this gave rise to the 'Project 502' group from industry, with Armstrong Whitworth Aircraft and Sperry in March and GEC in September.Template:Sfn

The 29 July 1949 update of the Staff Target called for a maximum range of Template:Convert and a minimum of Template:Convert. Maximum altitude should be 55,000 ft, but 45,000 would be considered acceptable. A further update pushed the range to Template:Convert against a Template:Convert, later Template:Convert, target. It was assumed the targets would "jink" at 1G, so the missile needed to maneuver at 4G at sea level and 2.5G at 40,000 ft. Additional requirements were the ability to switch between targets in 6 seconds.<ref name="Friedman2012p179"/>

The designers ultimately selected a maximum range of 30,000 yards, which included Template:Convert of coasting after motor burn-out. This was about 50% better than the contemporary US Terrier design. Hit probability was estimated to be 40% at maximum range,Template:Efn-lr so salvos of three missiles would be fired at once, demanding a three-place launcher. This was later reduced back to a twin-launcher when it was realized accessing the missile in the middle launcher would make maintenance difficult.<ref name="Friedman2012p179"/>

Changing requirements

When the deployment of the Seaslug was first being considered, three classes of custom missile-firing ships were considered. The Task Force Ship would be capable of Template:Convert and would tasked with fleet air defence, the Ocean Convoy Escort was a Template:Convert vessel that would provide direct cover over seagoing convoys, while the Template:Convert Coastal Convoy Escort would do the same for ships travelling closer to shore. At that time it was believed that aircraft carriers would be able to provide adequate cover over convoys or fleets in the ocean, so attention turned to the Coastal Convoy Escort. Beginning in May 1953 a Beachy Head-class repair ship, Template:HMS, was converted into a prototype escort ship to test this fitting.<ref>Template:Cite book</ref>

For this role, maximum storage density was essential, so the initial design featured a single booster rocket mounted at the missile’s base. This resulted in a very long missile that caused handling issues on small ships. Like most contemporary designs, the single inline booster was eventually replaced by four smaller boosters wrapped around the fuselage, reducing the overall length to about 20 ft (6.1 m). These boosters were positioned within the diameter defined by the missile’s wings, so they did not increase its storage diameter. However, if one booster failed to fire, the thrust would become significantly off-axis. This problem was later mitigated by moving the boosters forward, placing their exhaust near the missile’s centre of gravity, which allowed the small control surfaces to maintain effectiveness despite asymmetric thrust. By comparison, the American Terrier missile was shorter at 13 ft 6 in (4.11 m), but employed an additional tandem booster, bringing its total length to 28 ft 6 in (8.69 m).<ref name="Friedman2012p179"/>

In 1954, during another review of the Navy's future operations, consideration turned from a "hot war" against the Soviets to a series of "warm wars" in the third world. Among other changes brought about by this review, including the cancellation of a future all-gun cruiser class and ending further conversion of WWII-era destroyers to Type 15 frigates, the new environment meant that air cover by carriers could not be guaranteed, and the need for air defence for task-force sized groups became the primary concern. A cut to carrier construction, capping the fleet at four, released funds for missile ship construction. In October 1954, a new design emerged that demanded the speed to keep up with a fleet in combat, have guns limited to self-defence, and carrying a single twin-missile launcher.<ref name="Friedman2012p181">Template:Cite book</ref>

The designs were continually modified in order to find a suitable arrangement. They started as early as 1953 with a mid-sized cruiser of Template:Convert carrying 60 to 90 missiles and a crew of 900. Admiral Ralph Edwards pointed out it would be more useful to have a larger number of small ships with 10 to 20 missiles than one larger one, but attempts to design such a ship resulted in one with room for the weapons but not the crew needed to operate them. In May 1955 a wide variety of plans for designs between the two extremes were compared, ranging from 9,850 tons down to 4,550.<ref>Template:Cite book</ref> After continual comparison and revision, these plans finally gelled around what became the County-class destroyer.<ref name="Friedman2012p184">Template:Cite book</ref>

Testing

The firing of the first Seaslug test missile from HMS Girdle Ness (A387). This version is based on the RAE's early GPV, and retains the rear-mounted boosters before they moved forward on the "long round".

Test firings of the GAP-based examples, now known as Rocket Test Vehicle 1, or RTV.1, demonstrated beam riding in October 1956. The Navy had set a date of 1957 for a broad modernization of the fleet, so they desired Seaslug to be cleared for service in 1956. To this end, they accepted the use of liquid fuels in spite of the Navy's concerns with these fuels on ships. However, by 1956 a new solid fuel rocket had been developed at the Summerfield Research Station which provided the desired range.<ref name="Friedman2012p180">Template:Cite book</ref>

Continual tests took place over the next four years using both the Clausen Rolling Platform at RAE Aberporth and the Girdle Ness. A final series of tests at sea, which culminated in sixteen successful firings, finally cleared the missile for service in 1961.<ref name="Friedman2012p180"/> After more than 250 launches, the Seaslug Mark 1, also known as Guided Weapon System 1, or GWS.1, finally entered service in 1962 on County-class, each fitted with a single twin missile launcher and a complete weapon system with one fire control set and 30 missiles. The Seaslug-armed cruisers were cancelled in 1957.Template:Sfn

Seaslug needed height, range and bearing information for targets. By 1955 the Royal Navy considered using the Type 984 radar on Seaslug-armed cruisers and destroyers to provide this. During development, the projected weight of the radar doubled, to the point where it could still potentially be mounted on cruisers, but was rejected for destroyers because it would have meant sacrificing their 4.5 in gun armament. The gun armament was regarded as essential for the navy's wider role outside the hot war mission. The solution adopted with the first batch of the County-class destroyers was to network them with ships carrying Type 984. The destroyers were given a reduced version of the Comprehensive Display System (CDS), which was fed by a CDS-link receiver called DPD (Digital Picture Transmission or Translation).Template:Sfn<ref name=Boslaugh66>Template:Cite book</ref>

The final set for the County ships, actually more a cruiser type than a destroyer, was quite complex: a Type 965 radar for early warning (P-band, 450 kW peak power, range over 175 km), in the County Batch 2 the double antenna AKE-2 had two different frequency settings; a Type 992Q target indicator radar (3 GHz, 1.75 MW peak power, 90 km range); a Type 278 height finding set (80–90 km); a Type 901 missile guidance radar (X band, 70 km range), that in the Sea Slug Mk 2 had a continuous wave signal (but it was still a beam riding designation radar); a Type 904 fire control radar (used in the MRS-3 system, X-band, 50 kW, 35 km range) for surface targeting.<ref>Template:Cite web</ref>

Description

Seaslug Mark 2 on display at Explosion Museum of Naval Firepower, showing the prominent booster motors. To the right is a Sea Wolf.

The missile had four wrap-around booster motors that separated after launch. After separation, the main motor ignited to power the missile to the target. The booster motors were positioned at the side of the missile, but this unusual arrangement with the motor nozzles both angled outwards at 22.5° and 22.5° to the left, the missile entered a gentle roll at launch, evening out differences in the thrusts of the boosters. This meant that large stabilising fins as used on contemporary missiles in service with the Royal Air Force (Bloodhound) and the British Army (Thunderbird) were not required. Once the boosters were jettisoned the control surfaces became active.

Guidance was by radar beam-riding, the beam to be provided by Type 901 fire-control radar. There were four flight modes:

  • LOSBR (Line Of Sight, Beam Riding), in which the missile flew up a beam that tracked the target
  • CASWTD (Constant Angle of Sight With Terminal Dive), with the missile climbing at a low angle and then diving onto a low-altitude target at 45°, used against low flying targets at over 12,000 yards away
  • MICAWBER (Missile In Constant Altitude While BEam Riding), used against low level target approaching at 500–800 feet, it allows switching from CASWTD to LOSBR when the target is closing at the ship
  • Up and over: the standard surface attack mode, using the Type 901 radar slaved to the Type 903 in bearing; the missile is fired at high elevation and then depressed in order to strike the vessel with a steep dive, without arming the fuse.<ref>Template:Cite web</ref>

Electrical power when the missile was in flight was provided by a flux switching alternator with a six tooth rotor. "The 1.5 kVA Seaslug generator ran at 24,000 rev/min with a frequency of 2,400 Hz."<ref>Template:Cite book</ref>

Service performance

The Seaslug launcher mounted on the quarterdeck of HMS Glamorgan, circa 1972

Seaslug was considered a high-performance weapon in the 1960s, with a single-shot kill probability claimed as high as 92 percent. Other estimates are lower: 75 percent for the Mk 1 and 65 percent for the Mk 2.<ref>Template:Cite web</ref> The first four ships of the County-class destroyers (Batch 1) operated the Seaslug Mk 1, while the final four (Batch 2) were fitted with the Action Data Automation Weapons System (ADAWS) command and control system, which enabled them to carry the more capable Mk 2 version. A proposal to refit the Batch 1 ships with ADAWS was dropped in 1968.<ref>Template:Cite book</ref>

The final firing of the Seaslug Mk 1 occurred in December 1981, by Template:HMS, the last Batch 1 destroyer in operational service.<ref name="Dykes">Template:Cite web</ref> Template:HMS was later converted into a training ship, with her Seaslug systems removed to create space for classrooms. The conversion was completed in June 1986.<ref>Template:Cite web</ref> Fife and the remaining GWS2 ships were sold to Chile between 1982 and 1987. The British government initially proposed upgrading the ships with Sea Dart missile systems, but the Chileans declined, and the ships were transferred with Seaslug still fitted.<ref>Template:Cite book</ref> In Chilean service, the launchers were later removed and replaced by an extended flight deck.<ref>Template:Cite web</ref>

During the Falklands War, Seaslug Mk 2 missiles were deployed aboard Template:HMS and Template:HMS. Only one was launched against an aircraft, by Antrim, without success. On 21 May 1982, in Falkland Sound, Antrim, which had previously been struck by an unexploded 1,000 lb bomb that passed through the Seaslug magazine, fired a single missile (some sources state two)<ref>Template:Cite web</ref> at one of a second wave of attacking IAI Dagger fighters. The aircraft were flying too low to be acquired by the missile’s radar, so the launch was unguided. It was intended to deter the pilot and remove the exposed missile from the launcher, as it posed a fire hazard.<ref>Template:Cite book</ref>

The first combat use in a surface-to-surface role occurred on 26 May, when Glamorgan fired a Seaslug Mk 2 at the radar site near Port Stanley Airport, claiming the destruction of a radar installation and several helicopters.<ref>Template:Cite web</ref> Glamorgan conducted further bombardments using Seaslug missiles against the runway on 28 and 30 May.<ref name="Seaslug">Template:Cite web</ref> A total of six Seaslug Mk 2 missiles were launched during the campaign: four operational firings and two jettisoned for safety after Glamorgan was struck by a land-launched Exocet missile on 12 June.<ref>Template:Cite web</ref> Also during 1982, the Mk 2 variant was used as a target drone in Sea Dart missile trials, although reliability issues affected both systems.<ref name="Dykes"/>

Ship Date Target Result
Antrim 21 May 1982 Argentine IAI Dagger One unguided missile fired at a low-flying aircraft no hit.<ref>Template:Cite web</ref>
Glamorgan 26 May 1982 Port Stanley radar site One missile fired. No confirmed results.<ref>Template:Cite web</ref>
Glamorgan 28 May 1982 Port Stanley runway One missile fired at runway to scatter debris. No confirmed results.<ref name="Seaslug"/>
Glamorgan 30 May 1982 Port Stanley runway One missile fired to hinder runway use. Effectiveness unconfirmed.<ref name="Seaslug"/>
Glamorgan 12 June 1982 Jettisoned (post-Exocet hit) Two missiles jettisoned for safety. No engagement.<ref>Template:Cite web</ref>

Variants

HMS Girdle Ness (A387) test launches a production model Seaslug circa 1961. The forward mounted boosters are prominent.

There were two main variants of the Seaslug:

Mark 1 (GWS.1)

The Seaslug Mark 1 was powered by the solid-fuel Foxhound (390 kg fuel) sustainer motorTemplate:Efn-lr and Gosling (145 kg) booster motors. It had a radio proximity fuze and Template:Convert blast warhead.

The Mark 1 was a beam rider missile, meaning the target had to be continually illuminated by the directing radar, so the system was limited to engaging only the number of targets that there were radars to track and lock on.

Mark 2 (GWS.2)

The Seaslug Mark 2 was based on the aborted Blue Slug programme to develop an anti-ship missile using the Seaslug missile and guidance system. The project was cancelled in favour of the "Green Cheese" missile, a tactical nuclear anti-ship weapon, but other project developments were incorporated into what became the Mark 2. It had improved low altitude performance and a limited anti-ship capability and entered service in 1971. The Mark 2 utilized an improved beam-riding guidance system. and solid-state electronics. It was powered by the Deerhound sustainer motor, with Retriever boosters. Control was by a modified Type 901M radar and it had an improved infra-red proximity fuze and a continuous-rod warhead with a smaller, Template:Convert, explosive charge (RDX-TNT) and an unfold diameter of about 70 feet (10 mm steel rods were used)

The capabilities of the new Sea Slug Mk 2, an almost 2.5 ton missile, were much improved compared to the previous Mk 1. The boosters gave a total of about 60 tons-force, with Template:Convert fuel for each one (145 kg in the Mk 1), accelerating it to over Mach 2. When they separated because the extreme drag made by the rings all around the missile, the solid fuel sustainer Deerhound started to burn its Template:Convert of propellant (390 kg for the Mk 1) and gave about Template:Convert for 38 seconds. The slender missile remained at over Mach 2-2.5 until the flameout. The missile was made fully controllable about ten seconds after firing, followed by a radio-beacon while it was centered in the radar beam; and armed the infra-red proximity fuze at about Template:Convert from the target, if 'hot', while if 'cold' the missile was detonated by command sent from the ship.

The range could be even more than 35,000 yards, especially at high altitude, with head-on supersonic targets. One of the longest shots recorded was made by HMS Antrim against a target over Template:Convert away, with an impact at 34.500 with about 46 seconds flight time.<ref>Template:Cite web</ref> The missile was capable of reaching potentially even higher altitude and longer range than nominally attested: even after the engine flameout (over 40 seconds after launch), it retained very high speeds and one of them even surpassed Template:Convert before self-destructing, about one minute after the firing.<ref>Template:Cite web</ref>

For both Mark 1 and Mark 2 Sea Slug there were drill rounds (painted blue) for the purpose of training and display rounds (painted red) which could be loaded onto the launcher for port visits and public relations.

Nuclear variant (not built)

In addition, a nuclear-armed variant was planned using a low-yield fission warhead code-named Winkle. Winkle was never built as it was quickly supplanted by Pixie, a very small unboosted warhead with an all-plutonium fissile core tested at Maralinga, which was, in turn, replaced by Gwen — a British version of the US W54 Gnat unboosted warhead of approximate yield 0.5–2 kiloton of TNT-equivalent. The final warhead choice was Tony - a UK version of the W44 Tsetse boosted warhead, but all nuclear options for Seaslug were subsequently abandoned, and no nuclear-armed variant of Seaslug was ever deployed.

Operators

Map with Seaslug operators in blue

Royal Navy

The County-class destroyers were specifically built to carry Seaslug and its associated control equipment. The magazine was positioned amidships and missiles were assembled in a central gallery forward of the magazine before being passed to the launcher on the quarterdeck. The handling arrangements were designed with a nuclear-war environment in mind and were therefore entirely under cover.

Chilean Navy

Some of the County-class destroyers were sold to Chile for the Chilean Navy. The system was decommissioned after the rebuild of the four ships purchased by Chile in the early 1990s.

Former operators

Notes

Template:Notelist-lr

References

Template:Reflist

Bibliography

Bibliography

  • Naval Armament, Doug Richardson, Jane's Publishing, 1981, Template:ISBN

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Template:UKmissiles

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