WE.177

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An inert WE.177 bomb originally used for training, shown here on its trolley in a museum

WE.177 was the last British air-launched nuclear bomb. There were three versions, all free-fall and parachute-retarded. Two of these versions, WE.177B and WE.177C were thermonuclear weapons. The remaining version, WE.177A was a boosted fission weapon.

The WE.177A boosted fission weapon, deployed in 1971, was originally conceived as an Improved Kiloton Weapon to replace Red Beard a tactical kiloton-range bomb. WE.177A was a dual-purpose weapon, being used by RAF and Royal Navy fixed wing aircraft as a surface attack tactical bomb against land and sea surface targets. It could be delivered by several methods including low-level loft bombing. Forty-three were also deployed aboard Royal Navy surface vessels of frigate size and larger for use by embarked helicopters as an anti-submarine NDB (Nuclear Depth Bomb). WE.177B was originally intended for a strategic role as described below, and WE.177C was added later as a high-yield tactical bomb, also described in more detail below.

• WE.177A weighed 272kg (600lb), with a selectable yield of 10kT and 0.5kT. This was a boosted fission weapon. The 0.5kT yield was used only in the NDB role for detonation above 130ft (40m) in shallow coastal waters or in oceanic deep waters to limit damage to nearby shipping. The full 10kT yield was used below 130ft (40m) in deep oceanic waters where no shipping was at risk. The full 10kT yield was used by fixed wing aircraft for surface attack. It had airburst, ground burst or laydown options. Although this variant matched the original concept with an added NDB function, and was identified as the 'A' model, it was not the first to be deployed. Development was purposely delayed when the Skybolt ALBM was cancelled. Revised priority was then given to a bomb intended to extend the life (in a strategic role) of the Vulcan force. This stopgap weapon was WE.177B a thermonuclear parachute-retarded free-fall bomb based on a lengthened WE.177A casing, using as a thermonuclear primary the intended warhead for WE.177A. This was known as KATIE in WE.177B. and as KATIE A in WE.177A. Twenty WE.177A bombs were transferred to the RAF from the Royal Navy when the large carriers were decommissioned, and the remaining 43 that were assigned to the Navy's helicopters were retired in 1992. These were also capable of use by Sea Harriers. It was known to the Armed Services as 'Bomb, Aircraft, HE 600lb MC'. In this service jargon MC (Medium Capacity) referred to a nuclear weapon in the kiloton range. The suffix HC High Capacity referred to a weapon in the megaton range, although there were some anomalies.

• W.177B weighed 431kg (950lb), with a single yield of 450kT This was a thermonuclear bomb, comprised of two parts. The primary was KATIE referred to above, but without the variable yield facility or the NDB's hydrostatic fusing. KATIE was based on a British design known as CLEO, earlier known as Super Octopus, intended as the thermonuclear primary for RE.179, a British warhead for the British version of the cancelled Skybolt air-launched ballistic missile. The secondary (or fusion elements) of RE.179 were based on the US W-59 warhead and were known as SIMON. However, the W-59 primary used PBX-9404 and was considered by the British to be unsafe. The US W-44 primary was replaced with a British primary developed from CLEO that evolved into KATIE, that did not use the shock-sensitive PBX-9404. When Skybolt was cancelled RE.179 was adapted to become WE.177B and in a smaller form, the British warhead for Polaris. As WE.177B it had airburst, impact, or laydown options. Roughly, 'laydown' can be taken to mean a ground burst with a time delay enabling the bomber to escape the detonation. Numbers built are still uncertain but reliable sources put the figure at 53, and all were retired by August 1998. When Polaris became operational the Vulcan force continued in a tactical role with these and other bombs. With the retirement of the Vulcans, WE.177B was carried by successor aircraft, including Tornado.

• WE.177C weighed 431kg (950lb), with a single yield of 200kT. It was deployed only by RAF Germany in the tactical strike role, and used by Tornadoes and other strike aircraft. It was deployed probably from the early 1980's after deployment of Chevaline had begun. The history of both are intertwined. The primary of the first Polaris warhead (ET.317) was scrapped and not re-used on Chevaline. The secondary, known as REGGIE, was re-used in the Chevaline warhead with a new design of super-hardened primary. However, there were two warheads per Chevaline and three on the original Polaris. The one-in-three spare secondaries were then re-used as the secondaries of WE.177C matched with a 'converted' KATIE A as the primary. The 'conversion' (MoD description) probably entailed removal of the variable yield equipment and hydrostatic fusing. This primary and secondary were then installed in a casing identical to the WE.177B casing and ballasted to have similar weight and ballistic properties intended to minimise development time and cost. WE.177C was retired by August 1998. Numbers are speculative but based on hard evidence in declassified files of the number of Polaris ET.317 warheads and spares, a figure of between 48 and 60 is likely.

WE.177A

Type A, B and C weapons were carried by strike aircraft, including the Avro Vulcan, Blackburn Buccaneer, SEPECAT Jaguar, Panavia Tornado, and RAF Harrier. The Royal Navy Sea Harrier carried only WE.177A, slung beneath the starboard wing. At one time, eight Tornado squadrons were nuclear capable.

Two paint-schemes are known to have been used on WE.177:- [overall white] with orange and green bands (early paint-scheme from the 1960s) and [overall green] with red details (later paint-scheme from the mid-1970s onwards). Most of the examples of WE.177 training rounds in museums are of the green-painted variety.

All versions of WE.177 had air-burst capability, as evidenced by the white translucent window in the nose of the bomb which housed a radar altimeter.

WE.177B & C

As with all British thermonuclear weapons, the tritium gas used in the bomb core was purchased from the United States as part of the Anglo-US Barter Agreements that permitted the US to obtain UK weapons-grade plutonium in exchange for HEU, tritium and other specialised material uneconomical to produce in the UK in the very small quantities required. The plant at Chapelcross codenamed CANDLE was built to recover tritium from time-expired service weapons returned for servicing. It was then re-cycled after re-lifing. All boosted fission weapons use tritium (which decays with time) gradually reducing the designed fission yield by approx 4.4% per year. Reduction in the fission yield of a primary will reduce the thermonuclear yield by a similar proportion, or even lead to the thermonuclear fusion stage refusing to ignite. To maintain optimum yield all versions of WE.177 required servicing at intervals of three years or slightly more. The fully-sealed weapon was not designed to be serviced in-the-field by the user. This was the first British designed air-delivered weapon to adopt the US practice of returning the weapon to the manufacturer for service.

WE.177 tail arrangement

The safety and arming systems on the WE.177 series (Permissive Action Links) probably were similar to those used on comparable American nuclear weapons eg. B61 since most RAF strike aircraft were also able to deploy US-supplied dual-key nuclear weapons supplied under Project E terms since the 1950's to early 1990's. Systems would need to be similar or compatible to US systems. The physical safety characteristics of WE.177 were probably comparable eg. using the concept of being "one point safe", plus the ability to activate its thermal batteries and fry the circuitry if it detected unauthorised interference, although there is no hard evidence or published sources that can positively confirm this.

During the Falklands war of 1982, some Royal Navy ships were said in newspaper reports to have WE.177A bombs on board as they headed south. Warships and replenishment ships normally deployed with their assigned nuclear weapons during the Cold War. However, all bomb-containers were reputedly removed before the ships arrived in South Atlantic combat zone.

Retirement

Trident D5 is the UK's sole remaining nuclear weapons delivery system, believed armed with a strategic warhead also usable in the sub-strategic role formerly performed by WE.177. Various projects to produce a successor to WE.177 were abandoned.

Table of WE.177 Variants

Variant	Weight	Est. Yield	Operational
WE.177B	431 kg	450 kT	1966 - 1995
WE.177C	431 kg	200 kT	~1980 - 1998
WE.177A	272 kg	10/½ kT	1971 - 1992

References

• Cocroft, W; Thomas, R. Cold War, Building for Nuclear Confrontation 1946-1989, English Heritage, 2003. ISBN 1873592698 - Outdated and accuracy now suspect.
• [nuclearweaponarchive.org] - Outdated and accuracy now suspect.
• Moore, R; A Glossary of Nuclear Weapons, 'Prospero' Journal of the BROHP Spring 2004, a Visiting Fellow at the University of Southampton.
• [http://www.mcis.soton.ac.uk/Site_Files/pdf/nuclear_history/glossary.pdf
• Site of University of Southampton, Mountbatten Centre for International Studies.
• Various declassified files available at The National Archives, London.

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