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WE.177 was the designation of a range of tactical and strategic nuclear bombs used by the British Armed Forces. There were three versions; WE.177A was a boosted fission weapon, while WE.177B and WE.177C were thermonuclear weapons. All were delivered by fixed-wing aircraft and helicopters, although plans never implemented were for some in an anti-submarine mode to be delivered by Ikara missile. All types were parachute retarded. The first version to be fully deployed, WE.177B, was delivered to the Royal Air Force in September 1966 followed by deliveries of the WE.177A to the Royal Navy beginning in 1969,〔 and the RAF in 1971, after a delay caused by the need to produce the ET.317 warhead for the UK Polaris A3T first; and was followed by WE.177C deliveries to the RAF. The Navy weapons were retired by 1992 and all other weapons with the RAF were retired by 1998.〔 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 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. However, the W59 primary used PBX-9404 and was considered by the British to be unsafe due to the potential for 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 (or 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 lbs 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 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 W-58 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 W-59 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. The original Polaris blunt-body re-entry vehicle had a relatively slow (subsonic) terminal velocity, and as anti-ballistic missile systems became an area of active study, it seemed that it would be particularly vulnerable to attack. There were also concerns that ET.317 could be destroyed by a nearby nuclear explosion, whose X-rays could potentially damage the electronics in the trigger (Jennie) and whose neutron burst could cause the primary to "fizzle" in a partial criticality. These problems led to the development of the Chevaline system to improve the warhead's chance of avoiding ABMs, along with a new "super-hardened" primary (Harriet) that would be more resistant to radiation. A side-effect of this conversion was a reduction in warheads per missile from three to two, the extra space being used by the Chevaline's decoys. As the Chevaline upgrade was carried out, the now-redundant third warheads were adapted into the new WE.177C. This conversion consisted of removing the original primary and replacing them with WE.177A's Katie A. The new warhead was placed in existing WE.177B casings, and then ballasted to have identical weight and ballistics as WE.177B. 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. 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. A plant codenamed ''Candle'' located adjacent to the Chapelcross nuclear power station, near the town of Annan, Scotland, 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 nuclear yield by a similar proportion, or even lead to the thermonuclear fusion stage failing to ignite. To maintain optimum yield all versions of WE.177 required servicing at intervals of three years or slightly more. Normal servicing was carried out by specialist RAF teams. 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 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 U.S. 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 WE177 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 options, the stresses from the opening of the drogue parachutes being particularly severe at the speed anticipated for the TSR-2, the requirement stating a dropping speed of from Mach (M) 0.75 to M 1.15 at a height of 50 ft for TSR-2 and M 0.75 to M 0.95 for the 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 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 P.1154 (WE.177A). This involved releasing the weapon after a dive from 35,000 ft, with weapon release at between 15,000 ft and 10,000 ft and, for the TSR-2, at speeds between Mach 0.80 to Mach 2.05. Intended clearance by 1970 for other types of aircraft and delivery methods included: Later, the following aircraft were armed with WE.177: 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「WE.177」の詳細全文を読む スポンサード リンク
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