WE.177

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 lb 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 — 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. 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 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 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 were 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 from 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:

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 helicopters and Ikara systems (where fitted) as an anti-submarine NDB, 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. 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 carriers 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 the 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 the Tornado. 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. 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 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), were routinely carried on some Royal Navy warships and the associated 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. The Ministry of Defence 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 accompanying the Task Force. Coventry and Sheffield were both later destroyed by enemy action near the Falklands.

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 (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. 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.

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 and 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.

Preserved examples

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: