Sea Slug missile
Sea Slug was a first generation surface-to-air missile
Surface-to-air missile
A surface-to-air missile or ground-to-air missile is a missile designed to be launched from the ground to destroy aircraft or other missiles...

 designed by Armstrong Whitworth
Armstrong Whitworth
Sir W G Armstrong Whitworth & Co Ltd was a major British manufacturing company of the early years of the 20th century. Headquartered in Elswick, Newcastle upon Tyne, Armstrong Whitworth engaged in the construction of armaments, ships, locomotives, automobiles, and aircraft.-History:In 1847,...

 (later part of the Hawker Siddeley group) for use by the Royal Navy
Royal Navy
The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

. It came into operational service in the 1960s and was still in use at the time of the Falklands War
Falklands War
The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...


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.


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
Victory ship
The Victory ship was a type of cargo ship produced in large numbers by North American shipyards during World War II to replace shipping losses caused by German submarines...

 specially converted into prototype escort ship, HMS 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
County class destroyer
The County class was a class of guided missile destroyers, the first such vessels built by the Royal Navy. Designed specifically around the Sea Slug anti-aircraft missile system, the primary role of these ships was area air-defence around the aircraft carrier task force in the nuclear-war...

s, each fitted with a single twin missile launcher.


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
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 (Bristol Bloodhound) and the British Army
British Army
The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

 (English Electric Thunderbird
English Electric Thunderbird
The English Electric Thunderbird was a British surface to air missile produced for the British Army. The Thunderbird was primarily intended to attack higher altitude targets at ranges of up to thirty miles or so. AA guns were still used for lower altitude threats...

) 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:
  • 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
  • MICAWBER (Missile In Constant Altitude While BEam Riding), similar to CASWTD, but with a terminal low-level glide phase so that the Mark 2 variant could be used against ships. This mode suffered from problems associated with the surface of the water reflecting the guidance beam.

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.


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
Proximity fuze
A proximity fuze is a fuze that is designed to detonate an explosive device automatically when the distance to target becomes smaller than a predetermined value or when the target passes through a given plane...

 and 200 lb (90.7 kg) 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.
  • Particulars
    • Attack Velocity: 685 mi/h
    • Range: 30000 yards (27,432 m)
    • Ceiling: 55000 feet (16,764 m)

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
Green Cheese missile
The Green Cheese missile was a British radar-guided anti-ship tactical nuclear warhead missile project of the 1950s. It was developed by Fairey Aviation to be used by the Fairey Gannet shipborne anti-submarine warfare aircraft, and was originally called Fairey Project 7...

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, 56 lb (25.4 kg), explosive charge and large steel penetrator.
  • Particulars
    • Attack Velocity: 1370 mi/h
    • Range: 35000 yards (32,004 m)
    • Ceiling: 65000 feet (19,812 m)

Nuclear Variant (not built)

In addition, a nuclear-armed
Nuclear weapon
A nuclear weapon is an explosive device that derives its destructive force from nuclear reactions, either fission or a combination of fission and fusion. Both reactions release vast quantities of energy from relatively small amounts of matter. The first fission bomb test released the same amount...

 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
Nuclear weapon design
Nuclear weapon designs are physical, chemical, and engineering arrangements that cause the physics package of a nuclear weapon to detonate. There are three basic design types...

 warhead with an all-plutonium fissile core tested
British nuclear tests at Maralinga
British nuclear tests at Maralinga occurred between 1955 and 1963 at the Maralinga site, part of the Woomera Prohibited Area, in South Australia. A total of seven major nuclear tests were performed, with approximate yields ranging from 1 to 27 kilotons of TNT equivalent...

 at Maralinga
Maralinga, South Australia
Maralinga, South Australia in the remote western areas of South Australia was the home of the Maralinga Tjarutja, a southern Pitjantjatjara Indigenous Australian people. Maralinga was the site of the secret British nuclear tests in the 1950s. The site measures about 3,300 km² in area...

, which was, in turn, replaced by Gwen - an Anglicised version of
the US W54
The W54 was the smallest nuclear warhead deployed by the United States. It was a very compact implosion-type nuclear weapon design, designed for tactical use and had a very low yield for a nuclear weapon.- Development :...

 Gnat unboosted warhead of approximate yield 1/2 - 2 Kiloton (kt). The final warhead choice was Tony - a UK version of the W44
The W44 was an American nuclear warhead used on the ASROC tactical anti-submarine missile system.The W44 had basic dimensions of 13.75 inches diameter and 25.3 inches length, a weight of 170 pounds, and a yield of 10 kilotons....

Tsetse primary
The Tsetse was the common design nuclear fission bomb core for several Cold War designs for American nuclear and thermonuclear weapons, according to researcher Chuck Hansen....

Boosted fission weapon
A boosted fission weapon usually refers to a type of nuclear bomb that uses a small amount of fusion fuel to increase the rate, and thus yield, of a fission reaction. The neutrons released by the fusion reactions add to the neutrons released in the fission, as well as inducing the fission reactions...

 warhead, but all nuclear options for Sea Slug were subsequently abandoned, and no nuclear-armed variant of Sea Slug was ever deployed.


Royal Navy
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.

During the Falklands War
Falklands War
The Falklands War , also called the Falklands Conflict or Falklands Crisis, was fought in 1982 between Argentina and the United Kingdom over the disputed Falkland Islands and South Georgia and the South Sandwich Islands...

 Sea Slug was only launched once against an aircraft target, by HMS Antrim
HMS Antrim (D18)
HMS Antrim was a County-class destroyer of the Royal Navy launched on 19 October 1967. In the mid-1970s, the Royal Navy removed 'B' turret and replaced it with four Exocet launchers.-Falklands Conflict:...

, 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. However, it was fired again in anger, this time against an Argentine radar at Stanley
Stanley, Falkland Islands
Stanley is the capital and only true cityin the Falkland Islands. It is located on the isle of East Falkland, on a north-facing slope in one of the wettest parts of the islands. At the 2006 census, the city had a population of 2,115...

 airfield that the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...

 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
HMS Fife (D20)
HMS Fife was the first unit of the Batch 2 County-class destroyers of the Royal Navy. She had 'B' turret removed and replaced with four Exocet launchers in the mid-1970s. In 1979, Fife provided assistance to the Caribbean island of Dominica after the island was hit severely by Hurricane David...

 was converted to a training ship, and had her Sea Slug systems removed, freeing up large spaces for classrooms.

Chilean Navy
A number of the County Class destroyers were sold to Chile
Chile ,officially the Republic of Chile , is a country in South America occupying a long, narrow coastal strip between the Andes mountains to the east and the Pacific Ocean to the west. It borders Peru to the north, Bolivia to the northeast, Argentina to the east, and the Drake Passage in the far...

 for the Chilean Navy
Chilean Navy
-Independence Wars of Chile and Peru :The Chilean Navy dates back to 1817. A year before, following the Battle of Chacabuco, General Bernardo O'Higgins prophetically declared "this victory and another hundred shall be of no significance if we do not gain control of the sea".This led to the...

. The system was decommissioned after the rebuild of the four ships purchased by Chile in the early 90's.
The source of this article is wikipedia, the free encyclopedia.  The text of this article is licensed under the GFDL.