WE . 177 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 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 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 WE177 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 : Versions . WE . 177A . WE . 177A weighed 272 kg ( 600 lb ) , and had a variable yield of 10 kt or 0 . 5 kt . It was known to the Armed Services 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 NDB role for detonation above 130 ft ( 40 m ) in shallow coastal waters or in oceanic deep waters to limit damage to nearby shipping . The full 10 kt yield was used below 130 ft ( 40 m ) 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 options . Although this variant matched the original Improved Kiloton Weapon concept with an added NDB function , and was identified as the A model , it was not the first to be deployed due to the more pressing needs for the strategic B models . At least forty - three were deployed aboard Royal Navy surface vessels of frigate size and larger for use by embarked helicopter s as an anti - submarine NDB , starting in 1971 . The development of a shortened variant for the Ikara anti - submarine missile was abandoned when the requirement for Ikara to arm the Type 82 destroyer escorts for the CVA - 01 aircraft carriers lapsed . Ikara performed a similar function to the U . S . Navy ' s Asroc missile which could also carry a nuclear warhead . The addition of a nuclear option to Ikara was intended to significantly improve its kill probability , while providing the escort commander with an instant - response , all - weather , all - conditions weapon to deploy against time - urgent targets . Helicopter - delivered NDBs were not always immediately available due to fuel - state , other taskings , or expended weapons load . A further quantity of WE . 177As were procured for the FAA ' s fixed - wing strike aircraft . When the Navy ' s large aircraft carrier s were decommissioned , around twenty warheads were transferred to the RAF . The remaining weapons that were assigned to the Royal Navy were retired in 1992 . WE . 177B . WE . 177B weighed 457 kg ( 1007 . 5 lb ) , with a fixed yield of 450 kt . Although it weighed in excess of 1000 lb it was known in RAF Service as the " Bomb , Aircraft , HE 950lb MC " to differentiate it from the conventional " Bomb , Aircraft , 1000 lb GP HE " , which gave rise to its popular name " 950 " . WE . 177B had airburst , impact , or laydown options . 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 sub - strategic tactical role with these and other bombs assigned to the NATO SACEUR . With the retirement of the Vulcans , WE . 177B was carried by successor aircraft , including Tornado . WE . 177C . WE . 177C weighed 457 kg ( 1007 . 5 lb ) , with a fixed yield of 190 kt . WE . 177C was deployed only by RAF Germany in the tactical strike role , and used initially by the Jaguar and later by Tornadoes . It was deployed probably from the early 1970s after deployment of Chevaline had begun . 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 . Further development proposals . There were several proposals to adapt WE . 177A for other delivery systems . Among them were proposals to re - engineer the WE . 177A warhead into two submarine - launched heavyweight torpedoes which received some attention . The Mk . 24N Tigerfish nuclear - armed torpedo had approved project status for some years but was eventually shelved . Its raison d ' être was to overcome the performance shortcomings of the Tigerfish torpedo , and especially its failure to meet the dive - depth requirements needed to counter deep - diving Soviet SSNs and SSBNs that had outstripped western torpedo performance . < ref name = " PRO . DEFE 24 / 389 E42 " > PRO . DEFE 24 / 389 E42 < / ref > There was also a proposal endorsed by Flag Officer Submarines ( FOSM ) , the Royal Navy ' s professional head of the Submarine Service , to use the WE . 177A warhead in another torpedo , the shallow - running unguided Mk . 8 torpedo of World War II vintage . A Mk . 8 torpedo was chosen to sink the Argentinian warship Belgrano because it was of proven reliability , unlike the unreliable Tigerfish . This proposal did not gain approved project status although its raison d ' être was similar to that for Tigerfish , and intended to counter extended delays in Tigerfish development . FOSM ' s proposal stated that a 10 kt nuclear detonation at the Mk . 8 torpedo ' s running depth of approximately 40 ft ( 12 m ) would destroy a deep - diving SSN at 2 , 000 ft ( 610 m ) depth . The planned M4 - Minus version of the Ikara was also intended to have a nuclear depth charge option as an alternative to its intended payload of a Mark 44 or NAST 7511 torpedo . However , this was cancelled in 1966 . The M4 - Minus project was apparently cancelled altogether sometime later . Falklands War . During the Falklands war of 1982 , some Royal Navy ships had 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 bombs in their floatable containers were stated by the Ministry of Defence to have been off - loaded from the escort vessels HMS " Broadsword " , HMS " Brilliant " , HMS " Coventry " ( sunk in action ) , and HMS " Sheffield " ( sunk in action ) , for storage in the better - protected deep magazines aboard HMS " Hermes " , HMS " Invincible " and the Fleet Replenishment ships RFA " Fort Austin " , RFA " Regent " , RFA " Resource " and RFA " Fort Grange " accompanying the Task Force . HMS " Hermes " and HMS " Invincible " then had aboard 40 % and 25 % respectively of the entire Royal Navy stockpile of WE . 177A weapons and there was concern at their possible loss in action , and the consequences if a military emergency should develop simultaneously in the NATO area where these weapons were intended for use . It is not clear if the weapons were removed from deep storage on these vessels , before the Task Force engaged in action around the Falklands Islands , although the MoD assert that these ships did not enter Falklands Islands territorial waters or any other areas subject to the Treaty of Tlatelolco ( that established the Latin America Nuclear Weapons Free Zone ) that the UK was a signatory to . The MoD assert that the Task Force Commander - in - Chief was given instructions on deployment of his forces to avoid any breach of the treaty . They also state that all the nuclear weapons were returned to the UK aboard RFA " Fort Austin " and RFA " Resource " on 29 June and 20 July 1982 respectively , after the end of the Falklands War . Retirement . Reliable , recently published sources based upon recent research in declassified files in The National Archives , put eventual total numbers of all versions of WE . 177 at between 200 - 250 . All Royal Navy WE . 177A weapons were retired in 1992 . By August 1998 all RAF stock of all versions , had been withdrawn and dismantled . In the early 1990s the US withdrew all nuclear weapons that were assigned to British forces under NATO nuclear weapons sharing arrangements . Trident D5 is the UK ' s sole remaining nuclear weapons delivery system ( see " Vanguard " class submarine ) , 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 . Following retirement , a number of WE . 177 training rounds were donated to museums in the United Kingdom , and one was donated to the National Atomic Museum in Albuquerque , New Mexico , where it can be viewed alongside similar American weapons . Another is at RAF Hendon .