WE.177

The WE.177, originally styled as WE 177, and sometimes simply as WE177, was a series of tactical and strategic nuclear weapons with which the Royal Navy (RN) and the Royal Air Force (RAF) were equipped. It was the primary air-dropped nuclear weapon in the United Kingdom from the late 1960s into the 1990s. The underlying design was based on the US W59, which the UK had gained as part of their involvement in the GAM-87 Skybolt program. The RAF was not happy with the primary stage of the W59, which was potentially subject to accidental detonation when subject to mechanical shocks. Air Ministry Operational Requirement OR.1177 was issued for a new design using a less sensitive explosive, which was undertaken at the Atomic Weapons Research Establishment as "Cleo". When Skybolt was cancelled, the UK gained access to the UGM-27 Polaris missile and its W58 warhead, but they continued development of Cleo as a tactical weapon to replace Red Beard. A later requirement for a much smaller tactical and anti-submarine weapon for Navy use was filled by using the new primary as a boosted fission weapon. Three versions were produced, A, B and C. The first to be produced was the 450 kilotonnes of TNT (1,900 TJ) WE.177B, which entered service with the RAF at RAF Cottesmore in September 1966. Further deliveries were delayed by the need to complete the warheads for the Polaris A3T. The Navy did not begin to receive its ~10 kt (42 TJ) WE.177As until 1969. The 190 kt (800 TJ) C models for the RAF followed. All versions could be delivered by fixed-wing aircraft and could be parachute retarded. The WE.177A, in anti-submarine mode, could also be carried by helicopters. The Navy weapons were retired by 1992, and all other weapons with the RAF were retired by 1998. When it was finally withdrawn in 1998, the WE.177 had been in service longer than any other British nuclear weapon. The WE.177 was the last nuclear bomb in service with the Royal Air Force, and the last tactical nuclear weapon deployed by the UK.

History In May 1960, Prime Minister Harold Macmillan signed an agreement with President Eisenhower to purchase 144 AGM-48 Skybolt missiles for the UKs V bomber force. Along with the missiles, the UK would receive the design of the Skybolt's W59 warhead, which was much smaller and lighter than even the smallest UK designs of the era. The UK version would be known by the codename RE.179. The W59 primary (fission elements) used a polymer-bonded explosive codenamed PBX-9404. The British considered this to be unsafe, due to the potential for mechanical shocks to set off the PBX. Since the late 1950s, they had been working on their own primary design, originally 'Octopus', and then 'Super Octopus', that used more explosive and less fissile material, and was shock-insensitive as well. They proposed adapting the Super Octopus design for use in RE.179, calling the new version 'Cleo'. Cleo designs were tested underground at the Nevada Test Site in 1962. The secondary (fusion elements) of RE.179 remained identical to the W59's, and were known as 'Simon' in WE.177B, and as 'Reggie' in the ET.317 version for UK Polaris. At the time, the UK's only tactical nuclear weapon was Red Beard, a relatively large weapon of 2,000 pounds (900 kg) weight. While work continued on Cleo, it was decided to adapt it as a weapon of its own to replace Red Beard, as the 'Improved Kiloton Weapon'. The adapted version of the primary, now the only part of the physics package, became 'Katie'. Katie would be used in a new bomb casing to produce WE.177A, replacing Red Beard with a weapon of roughly 1/3 the weight, and much smaller size. WE.177A would also be used by the Royal Navy, both for surface attack, as well as a nuclear depth bomb, or NDB. When AGM-48 Skybolt was cancelled, part of the resulting Nassau Agreement was the replacement of Skybolt with the Polaris missile. Polaris A3T used its own warhead design, W58. The W58 was also rejected by the British because it also used PBX-9404 in its primary. The UK solution was to adapt their RE.179 for the UK Polaris, and assigned the codename ET.317. The need for ET.317 warheads for UK Polaris was urgent, and development of the Improved Kiloton Bomb was temporarily halted until the Polaris warhead programme was completed. To fill the gap until Polaris entered service, it was necessary to provide RAF strategic bombers with a suitable weapon that would allow them to penetrate Warsaw Pact defences at low-level, minimising attrition from air defences. WE.177 was adapted to produce a high-yield interim strategic weapon for the five-year period, while the Polaris submarine force was building. Halting work on the original WE.177, now known as the 'A' model, a new version that used the W59 secondary, codenamed Simon, matched with a modified 'Katie B' primary created WE.177B. This version required a lengthened bomb casing, and was somewhat longer and heavier than WE.177A.

During the Chevaline program, the number of warheads on each Polaris missile was reduced from three to two. These now-redundant third warheads were adapted into the new WE.177C. This conversion consisted of removing the original primary, and replacing them with Katie A from the WE.177As. The new warhead was placed in existing WE.177B casings, and then ballasted to have identical weight and ballistics as the WE.177B.

Deployment and usage

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