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Image shows a museum exhibit of a WE.177, which was Britain's last free-fall nuclear bomb.  The example shown is a decommissioned training example, re-painted in its 'live' green colour scheme.  It is on display at the Imperial War Museum North, in Manchester, England.
WE.177 nuclear bomb at the
Imperial War Museum North.
Type Free-fall gravity nuclear bomb
Place of origin United Kingdom[1]
Service history
In service September 1966–1998[1][2][3]
Used by British Armed Forces:
*Royal Navy,
*Royal Air Force
Wars Cold War
Production history
Designer Atomic Weapons Research Establishment (AWRE), Aldermaston[2]
Manufacturer Atomic Weapons Research Establishment (AWRE), Aldermaston[2]
Unit cost unknown
No. built ~319
Variants WE.177A, WE.177B, WE.177C
Weight WE.177A: 272 kilograms (599.7 lb),[1][3]
WE.177B: 457 kilograms (1,007.5 lb),[1]
WE.177C: 457 kilograms (1,007.5 lb)[1]
Length WE.177A: 112 inches (284.5 cm),[1]
WE.177B: 133 inches (337.8 cm),[1]
WE.177C: 133 inches (337.8 cm)[1]
Diameter all: 16 inches (40.6 cm),[1]

Filling WE.177A: ZA297 primary fission warhead,[1]
WE.177B: ZA297 primary fission warhead & PT176 secondary thermonuclear fusion warhead,[1]
WE.177C: ZA297 primary fission warhead & PT176 secondary thermonuclear fusion warhead,[1]
Filling weight unknown
Blast yield WE.177A: 0.5 kilotons or 10 kilotons[1]
WE.177B: 450 kilotons[1]
WE.177C: 200 kilotons[1]

The WE.177, originally known as WE 177,[1][2] and sometimes incorrectly known as WE177,[3][4] was the military designation of a range of aircraft delivered tactical and strategic gravity free-fall nuclear bombs made available to and deployed by two services of the British Armed Forces; namely the Royal Navy (RN) and the Royal Air Force (RAF). WE.177 was created at the request of the British Air Ministry to meet the Operational Requirement OR.1177,[1] and one variant entered service in 1966, initially with only the Royal Air Force.[1]

There were three versions; WE.177A was a boosted fission weapon, while WE.177B and WE.177C were thermonuclear weapons.[2] All could be delivered by fixed-wing aircraft, and also, in the case of the WE.177A, in anti-submarine mode,[4] by helicopters and by the Ikara missile system. All types could be parachute retarded.[3]

The first version to be fully deployed, the WE.177B,[1] was delivered to the Royal Air Force (RAF) at RAF Cottesmore in September 1966,[2] followed by deliveries of the WE.177A to the Royal Navy (RN)[1][2] beginning in 1969,[5] and the RAF[1] 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.[2][3] When it was finally withdrawn in 1998, the WE.177 had been in service longer than any other British nuclear weapon.[2]

The WE.177 was the last nuclear bomb in service with the Royal Air Force, and the last tactical nuclear weapon deployed by the United Kingdom (UK).


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.

However, the W59 primary used a polymer-bonded explosive; codenamed 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.[2] 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 pounds (907 kg) weight. While work continued on Cleo, it was decided to adapt it as a weapon of its own to replace Red Beard,[3] 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,[4] 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.

Rare WE.177A sectioned[6] instructional example of an operational round, one of only two in existence, seen here at Boscombe Down Aviation Collection.[7]

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 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[edit]

A WE.177B or C training round for ground instructional purposes. Externally identical to operational rounds, but manufactured in steel rather than aluminium alloy, and inert; i.e., does not contain any fissile materials, explosives, or other hazardous components. The red canister contains the cable required to connect the weapon to the aircraft systems. The white 'X's cover cartridge-operated ejection ports, and signify that as an inert round, explosive charges are not installed. 'Live' WE.177 bombs had a two inch wide orange band around the circumference of the nose.[8]

Type A, B and C weapons were carried by strike aircraft, including the Avro Vulcan,[2] de Havilland Sea Vixen, Blackburn Buccaneer,[2] SEPECAT Jaguar,[2] and Panavia Tornado.[2][3] The Royal Navy Sea Harrier[2][4] 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),[9] and overall green with red details[2][8] (later paint scheme from the mid-1970s onwards).[10] 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 re-lifing. 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. To maintain optimum yield, all versions of WE.177 required routine maintenance at intervals of three years or slightly more. Normal servicing was carried out by specialist teams of RAF Armourers.

WE.177 safety and arming keys. The large white plastic part is the tool used to remove the protective cover from the lock.

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 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[3] options. The stresses from the opening of the drogue parachutes 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 50 feet (15 m) 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.[11]

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 35,000 feet (10,700 m), with weapon release at between 15,000 feet (4,600 m) and 10,000 feet (3,000 m), and, for the TSR-2, at speeds from Mach 0.80 to Mach 2.05.[citation needed]

Intended clearance by 1970 for other types of aircraft and delivery methods included:

aircraft and delivery methods
aircraft version delivery methods
Handley Page Victor Mk.2 WE.177A/B laydown, ballistic, retarded[disambiguation needed]
Avro Vulcan[2] WE.177A/B laydown, ballistic, retarded
Vickers Valiant Mks: B.1, P.R., K.1., P.R.K.1 WE.177A laydown, ballistic, retarded
BAC TSR-2[2] WE.177A/B laydown, ballistic, retarded, loft, dive toss
English Electric Canberra Mk.B.15 & B.16 WE.177A laydown, ballistic, retarded, loft
Blackburn Buccaneer Mk.2[2] WE.177A laydown, loft, retarded
Sea Vixen Mk.2 WE.177A laydown, loft, retarded
Westland Wasp WE.177A depth charge
Westland Lynx HAS.1 WE.177A depth charge
Westland Wessex HAS.3 WE.177A depth charge
Westland Wessex HUS WE.177A depth charge
Ikara (missile) WE.177A depth charge
Hawker Siddeley P.1154 WE.177A laydown, loft, retarded (RN)
Hawker Siddeley P.1154 WE.177A laydown, loft, dive toss (RAF)
Hawker Siddeley Nimrod WE.177A depth charge

Later, the following aircraft were armed with WE.177:

aircraft and delivery methods (later)
aircraft version delivery methods
Blackburn Buccaneer Mk.2[2] WE.177A/B/C laydown, loft, retarded
Panavia Tornado GR.1, GR.1A, GR.4, GR.4A[2][3] WE.177A/B/C laydown, loft, retarded
SEPECAT Jaguar[2] WE.177A laydown, loft, retarded
BAe Sea Harrier FRS1[2][4] WE.177A laydown, loft, retarded



The addition of a nuclear option to Ikara

WE.177A weighed 272 kilograms (599.7 lb),[3] and had a variable yield of 10 kilotonnes (9,842 long tons; 11,023 short tons) or 0.5 kilotonnes (492 long tons; 551 short tons). It was known to the British Armed Forces as 'Bomb, Aircraft, HE 600lb MC'.[4] '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 130 feet (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 feet (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.[3] It had air burst, ground burst or laydown delivery options.[3]

Although this variant matched the original Improved Kiloton Weapon concept with an added nuclear depth bomb 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.[2] At least forty-three were deployed aboard Royal Navy surface vessels of frigate size and larger; for use by embarked helicopters and Ikara systems (where fitted) as an anti-submarine nuclear depth bomb,[4] starting in 1971. 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.[citation needed] Helicopter-delivered nuclear depth bombs 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 Fleet Air Arm's (FAA) fixed-wing strike aircraft. When the Navy's large aircraft carriers were decommissioned, around twenty warheads were transferred to the Royal Air Force. The remaining weapons that were assigned to the Royal Navy were retired in 1992.


WE.177B & C

WE.177B weighed 457 kilograms (1,007.5 lb), with a fixed yield of 450 kilotonnes (442,893 long tons; 496,040 short tons). Although it weighed in excess of 1000 lb, it was known in RAF Service as the 'Bomb, Aircraft, HE 950lb MC',[citation needed] 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 fifty-three (53), and all were retired by August 1998.[2] 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 the Panavia Tornado.[2]


WE.177C weighed 457 kilograms (1,007.5 lb), with a fixed yield of 190 kilotonnes (186,999 long tons; 209,439 short tons).

WE.177C was deployed only in RAF Germany; in the tactical strike role, and used initially by the Jaguar,[2] and later by the Tornado.[2][3] It was deployed probably from the early 1970s, after deployment of Chevaline had begun. WE.177C was retired by August 1998.[2] 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 forty-eight (48) and sixty (60) is likely.[original research?]

variant weight length estimated yield operational
WE.177A 282 kg (621.7 lb)[3] 112 in (284.5 cm) 0.5 kt (492 long tons; 551 short tons), or
10 kt (9,842 long tons; 11,023 short tons)
1969–1992 ~107
WE.177B 457 kg (1,007.5 lb) 133 in (337.8 cm) 450 kt (442,893 long tons; 496,040 short tons) 1966–1995 ~53
WE.177C 457 kg (1,007.5 lb) 133 in (337.8 cm) 200 kt (196,841 long tons; 220,462 short tons) ~1980–1998 ~159
total ~319

Further development proposals[edit]

Detail of the official WE.177 project tie. The WE.177 project was denied a project tie for many years, because the project code was, unusually, itself classified. The symbols represent atoms: hydrogen, above two atoms of nitrogen; atomic numbers 1, 7, and 7, respectively.

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.[5] 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.[5] A Mk.8 torpedo was chosen to sink the Argentinian warship General 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 feet (12 m) would destroy a deep-diving SSN at 2,000 feet (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 Conflict[edit]

During the Cold War, WE.177A bombs, generally intended for use as depth charges (though able to be delivered in any operational mode by the Sea Harrier FRS1),[12] were routinely carried on some Royal Navy warships,[4] and the associated Royal Fleet Auxiliary (RFA) replenishment ships. They were kept in containers that were designed to float if they ended up in the sea. In 1982, with the outbreak of the Falklands War, some of these vessels were urgently assigned to the Naval Task Force, and began to steam south with their nuclear weapons still on board.[4] The Ministry of Defence (MoD) has said that, en-route, the bombs were offloaded from escort vessels Broadsword, Brilliant, Coventry, and Sheffield; and were stored in the better-protected deep magazines aboard Hermes, Invincible; and the fleet replenishment ships Fort Austin, Regent, Resource, and Fort Grange who were accompanying the Task Force. Coventry and Sheffield were both later destroyed by enemy action near the Falkland Islands.[4]

It is not clear if the weapons were removed from deep storage on these vessels before the Task Force engaged in action around the Falkland Islands, although the MoD assert that these ships did not enter Falkland Islands territorial waters, or any other areas subject to the Treaty of Tlatelolco[4] (that established the Latin America Nuclear Weapons Free Zone), to which the UK was a signatory. 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.[4] They also state that all the nuclear weapons were returned to the UK aboard the Royal Fleet Auxiliaries Fort Austin and Resource on 29 June and 20 July 1982 respectively, after the end of the Falklands War.[4]


Reliable, recently published sources based upon recent research in declassified files in The National Archives (TNA), put eventual total numbers of all versions of WE.177 at between 200 and 250.[13] All Royal Navy WE.177A weapons were retired in 1992. By August 1998, all RAF stock of all versions had been withdrawn and dismantled.[2] 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.

Preserved examples[edit]

WE.177 training round at the Science Museum, London.
Two WE.177 training rounds at the Royal Air Force Museum Cosford.
WE.177 training round at Hack Green Secret Nuclear Bunker.

Two inert WE.177A operational rounds are on display:

In addition, a number of WE.177 training rounds were donated to museums in the United Kingdom and one in the United States. Examples are on display at:

See also[edit]



  1. ^ a b c d e f g h i j k l m n o p q r s t u Dr Richard Moore (March 2004). UK Nuclear History, Working Paper, Number: 1; The Real Meaning of the Words: a Pedantic Glossary of British Nuclear Weapons (pdf). Mountbatten Centre for International Studies (MCIS) (Report). University of Southampton. 
  2. ^ a b c d e f g h i j k l m n o p q r s t u v w x y z aa ab ac ad "Atomic Weapons Establishment > About AWE > History > WE.177 free-fall bomb enters service". AWE.co.uk. Burghfield: Atomic Weapons Establishment (AWE). Archived from the original on 28 September 2007. 
  3. ^ a b c d e f g h i j k l m n "Nuclear Weapons Database: United Kingdom arsenal". CDI.org. Center for Defense Information (CDI), Washington, D.C. 2 January 1997. Archived from the original on 6 November 2011. 
  4. ^ a b c d e f g h i j k l m Operation CORPORATE 1982 - the carriage of nuclear weapons by the Task Group assembled for the Falklands campaign (PDF). CBRN Policy (Report). United Kingdom Ministry of Defence. Archived from the original (PDF) on 26 October 2012. 
  5. ^ a b c Public Record Office (PRO), London. DEFE 24/389 E 42 Annex Appendix 1, June 1969.
  6. ^ "engineering drawing depicting colour-coded two-dimensional sectional views of the WE.177A and WE.177B/C" (png image). Nuclear-Weapons.info. Brian Burnell's guide to British nuclear weapon projects. Retrieved 22 May 2017. 
  7. ^ "Exhibits". BoscombeDownAviationCollection.co.uk. Boscombe Down Aviation CollectionOld Sarum Airfield, Salisbury. 
  8. ^ a b "Photograph of RAF Armourers with a live WE.177 (B or C) nuclear bomb, and its associated WE.155 storage and transport container" (png image). Nuclear-Weapons.info. Brian Burnell's guide to British nuclear weapon projects. Retrieved 22 May 2017. 
  9. ^ "Black and white photograph of a live WE.177 nuclear bomb in early white colour scheme, on a trolley". CDI.org. Center for Defense Information (CDI), Washington, D.C. Archived from the original (jpg image) on 14 February 2012. 
  10. ^ "Colour photograph of a training version of the WE.177 nuclear bomb, re-painted in hi-gloss green. Original training versions (of all models) were painted blue.". Skomer.u-net.com. Skomer. Archived from the original (jpg image) on 4 February 2012. 
  11. ^ Public Record Office (PRO), London. TNA AIR 2/17328 E3A p1
  12. ^ Although the Sea Harrier's pilot was able to select both the 'low' and 'high' yield depth charge modes, the aircraft was never cleared for this mode of delivery
  13. ^ Various declassified files available at The National Archives (TNA), Kew, London.

Further reading[edit]

External links[edit]