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 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 When it was finally withdrawn in 1998, the WE.177 had been in service longer than any other British nuclear weapon.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 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
Type A, B and C weapons were carried by strike aircraft, including the Avro Vulcan, de Havilland Sea Vixen, Blackburn Buccaneer, SEPECAT Jaguar, and Panavia Tornado. The Royal Navy Sea Harrier carried only WE.177A, slung beneath the starboard wing. The B and C models were too large for this aircraft. At one time, eight Tornado squadrons were nuclear capable.
Three paint schemes are known to have been used on WE.177; overall white with red and yellow bands (early paint scheme from the 1960s), and overall green with red details (later paint scheme from the mid-1970s onwards). The drill weapon used for loading and flight drills was Oxford blue. This was so that a live round could easily be identified, but service procedures required all training rounds to be treated and handled as if they were live. The training rounds even returned the correct indications to the carrying aircraft systems if they were 'armed' in flight. Most of the examples of WE.177 training rounds in museums have been re-painted in green, presumably to look like the original live rounds — an example re-painted green is located on the ground underneath the port wing of the Tornado at the Midland Air Museum.
As with all British thermonuclear weapons, the tritium gas used in the bomb core was purchased from the United States as part of the 1958 US–UK Mutual Defence Agreement; that permitted the US to obtain UK weapons-grade plutonium, in exchange for enriched uranium, tritium, and other specialised material uneconomical to produce in the UK in the very small quantities required. An industrial plant codenamed Candle located adjacent to the Chapelcross nuclear power station, near the town of Annan, Dumfries and Galloway, Scotland, was built to recover tritium from time-expired service weapons returned for routine maintenance or servicing. It was then recycled after removal of tritium decay products. All boosted fission weapons use tritium, which decays with time, reducing the designed fission yield by approx 4.4% per year. Reduction in the fission yield of a primary will reduce the thermonuclear nuclear yield by a similar proportion, or even lead to the thermonuclear fusion stage failing to ignite (known as a "fizzle"). To maintain optimum yield, all versions of WE.177 required routine maintenance about every three years. Normal servicing was carried out by specialist teams of RAF Armourers.
Part of the safety and arming system on the WE.177 series was a simple key-operated Strike Enable Facility; using a cylindrical barrel key similar to those used on vending or gaming machines. By agreement with the owners of the lock's design rights, the key profile for each and every live weapon was unique, and would not be used for any other purpose. The profile for the training rounds was also not used elsewhere, but all training rounds used the same profile. The physical safety characteristics of WE.177 were probably comparable to similar US weapons, e.g. using the concept of being 'one-point-safe'. The safety and arming system was more sophisticated than on a conventional shell or bomb. The WE.177 safety and arming system had three safety breaks (which varied according to delivery mode) in the arming chain, whereas a conventional weapon only requires two.
The casing of WE.177 was unusually robust, and complicated, for a British air-dropped bomb; made necessary by the requirement for the laydown delivery options. The stresses from the opening of the drogue parachutes (3 for the A version, 4 for the heavier B/C variants) were particularly severe at the speed anticipated for the BAC TSR-2, the requirement stating a dropping speed of from Mach number M 0.75 to M 1.15, at a height of for TSR-2; and M 0.75 to M 0.95 for the Blackburn Buccaneer. This, together with the 'slap down' of the tail on impact required a strong, well-engineered bomb casing to ensure the enclosed warhead remained intact.
Apart from the laydown delivery requirement, the weapon was also required to be used in a 'dive toss' mode; from both the TSR-2 (WE.177A/B), and the RAF version of the Hawker Siddeley P.1154 (WE.177A). This involved releasing the weapon after a dive from , with weapon release at between and , and, for the TSR-2, at speeds from Mach 0.80 to Mach 2.05.
Intended clearance by 1970 for other types of aircraft and delivery methods included: +aircraft and delivery methodsaircraftversiondelivery methodsHandley Page Victor Mk.2WE.177A/Blaydown, ballistic, retardedAvro VulcanWE.177A/Blaydown, ballistic, retardedVickers Valiant Mks: B.1, P.R., K.1., P.R.K.1WE.177Alaydown, ballistic, retardedBAC TSR-2WE.177A/Blaydown, ballistic, retarded, loft, dive tossEnglish Electric Canberra Mk.B.15 & B.16WE.177Alaydown, ballistic, retarded, loftBlackburn Buccaneer Mk.2WE.177Alaydown, loft, retardedSea Vixen Mk.2WE.177Alaydown, loft, retardedWestland WaspWE.177Adepth chargeWestland Lynx HAS.1WE.177Adepth chargeWestland Wessex HAS.3WE.177Adepth chargeWestland Wessex HUSWE.177Adepth chargeHawker Siddeley NimrodWE.177Adepth charge Later, the following aircraft were armed with WE.177: +aircraft and delivery methods (later)aircraftversiondelivery methodsBlackburn Buccaneer Mk.2WE.177A/B/Claydown, loft, retardedPanavia Tornado GR.1, GR.1A, GR.4, GR.4AWE.177A/B/CloftSEPECAT JaguarWE.177Alaydown, loft, retardedBAe Sea Harrier FRS1WE.177Alaydown, loft, retarded
Versions WE.177A
WE.177A weighed , and had a variable yield of 10 kt (42 TJ) or 0.5 kt (2 TJ). It was known to the British Armed Forces as 'Bomb, Aircraft, HE 600lb MC'. '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.
The 0.5 kt yield was used only in the nuclear depth bomb role for detonation above in shallow coastal waters, or in oceanic deep waters to limit damage to nearby shipping. The full 10 kt yield was used below in deep oceanic waters where no shipping was at risk. The full 10 kt yield was also used by fixed-wing aircraft for surface attack. It had air burst, ground burst or laydown delivery options.