Sea Slug ( missile ) Sea Slug was a first generation surface - to - air missile designed by Armstrong Whitworth ( later part of the Hawker Siddeley group ) for use by the Royal Navy . It came into operational service in the 1960s and was still in use at the time of the Falklands War . Sea Slug was intended to engage high - flying targets such as reconnaissance aircraft or bombers before they could launch stand - off weapons . Later improvements meant that it could also be used against ships . Development . Work on what became Sea Slug began in 1949 under ' Stage 1 ' of the Royal Navy ' s post - war missile program . The weapon was intended to counter high - altitude nuclear - armed bombers before they could release their weapons . Development made use of on an earlier programme by the Fairey Aviation Company known as " LOPGAP " ( Liquid Oxygen / Petrol Guided Anti - aircraft Projectile ) , and a Victory Ship specially converted into prototype escort ship , RFA " Girdle Ness " , was procured . The original system differed in having a triple launcher . The Sea Slug Mark 1 finally entered service in 1961 on County class destroyer s , each fitted with a single twin missile launcher . Description . The missile had four wrap - around booster motors which separated after launch . After separation the main motor ignited to power the missile to the target . The booster motors were positioned at the front of the missile , but this unusual arrangement gave acceleration , and , with the motor nozzles angled outwards at 45° , 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 ( Bristol Bloodhound ) and the British Army ( English Electric Thunderbird ) were not required . Once the boosters were clear the control surfaces became active . Guidance was by radar beam - riding , the beam to be provided by Type 901 fire - control radar . There were 3 flight modes : Service performance . Sea Slug was a high - performance weapon in its day , with a single - shot kill probability of 92 % . It was , however , limited by the complicated handling arrangements and since each County class ship carried only a single fire - control radar only one target could be engaged at once , though two missiles could be fired against it . Variants . There were two main variants of the Sea Slug : Mark 1 ( GWS . 1 ) . The Sea Slug Mark 1 was powered by the " NK . 1 " liquid sustainer rocket motor and " Gosling " booster motor . It had a radio proximity fuze and 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 Sea Slug Mark 2 was based on the aborted Blue Slug programme to develop an anti - ship missile using the Sea Slug missile and guidance system . The project was cancelled in favour of the " Green Cheese missile " 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 1965 . The Mark2 utilized a semi - active homing guidance system , which allowed for other targets to be illuminated while the first target was engaged . It was initially powered by the " Foxhound " sustainer motor , later replaced by the " Deerhound " , 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 , , explosive charge and large steel penetrator . 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 " - an Anglicised version of the US W54 " Gnat " unboosted warhead of approximate yield 1 / 2 - 2 Kiloton ( kt ) . The final warhead choice was " Tony " - a UK version of the W44 " Tsetse " boosted warhead , but all nuclear options for Sea Slug were subsequently abandoned , and no nuclear - armed variant of Sea Slug was ever deployed . The County - class destroyers were specifically built to carry Sea Slug 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 . Operators . During the Falklands War Sea Slug was only launched once against an aircraft target , by HMS " Antrim " , and did not hit . This is hardly surprising , as the Royal Navy considered the system to be obsolete and the low - level attacks experienced in the Falklands War were outside the missile ' s operational capacity . It was fired again in anger , this time against an Argentine radar at Stanley airfield that the Royal Air Force had been unable to destroy . During a shore bombardment HMS Glamorgan triangulated the last known position of the radar with her ESM and fired a Sea Slug . She later fired several at the runway to cover it with debris which would have damaged any aircraft attempting to land or take off . Results , if any , are unknown , but the impressive fireworks display associated with the launch sequence was something of a morale booster to the troops ashore . Sea Slug was withdrawn as the Counties were decommissioned . HMS " Fife " was converted to a training ship , and had her Sea Slug systems removed , freeing up large spaces for classrooms . 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 .