WE.177

WE.177 was the last air-launched nuclear bomb of 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 could be delivered by air, and were typically parachute-retarded.

The first version to be deployed, WE.177B, was delivered to the Royal Air Force in September 1966 followed by deliveries of WE.177A to the Royal Navy beginning in 1969, [Public Record Office, London. (PRO) DEFE 24/389 E 42 Annex Appendix 1, June 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. [ [http://www.awe.co.uk/main_site/about_awe/history/timeline/1966/index.html WE.177 Free-Fall Bomb Enters Service] , AWE timeline]

History

In May 1960 Prime Minister Macmillan signed an agreement with President Eisenhower to purchase 144 AGM-48 Skybolt missiles for their 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 as 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".

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.177, replacing Red Beard with a weapon of roughly 1/3rd the weight and much smaller size. WE.177 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 used its own warhead design, W58, but given that both missiles were based on similar needs and technology, the W59 was unsurprisingly very similar. The UK decided to adapt their RE.179 for the Polaris instead of starting over with the W58, producing a smaller version known as ET.317. The need for ET.317 nuclear material was so pressing that development of the original WE.177 was halted.

WE.177 was so much better than the UK's existing weapons that it was also decided to adapt it as an interim strategic weapon while they waited for Polaris to enter service. Halting work on the original WE.177, now known as the "A" model, a new version that used the ER.317 secondary with a modified "Katie B" primary created the WE.177B. This version required a lengthened bomb casing, and was somewhat larger than WE.177A.

The original Polaris 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 particularily vulnerable to attack. There were also concerns that the ET.317 could be destroyed by a nearby nuclear explosion, who's X-rays could potentially damage the electronics in the trigger and who's 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 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 the 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 the WE.177B.

Type A, B and C weapons were carried by strike aircraft, including the Avro Vulcan, Blackburn Buccaneer, SEPECAT Jaguar, Panavia Tornado, and RAF Harrier. 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; [http://www.cdi.org/issues/nukef&f/database/we177.jpgoverall white] with red and yellow bands (early paint-scheme from the 1960s) and [http://www.skomer.u-net.com/projects/images/we177.jpgoverall green] with red details (later paint-scheme from the mid-1970s onwards). The drill weapon used for loading and flight drills was dark blue. Most of the examples of WE.177 training rounds in museums are of the green-painted variety.

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. The fully-sealed weapon was not designed to be serviced in-the-field by the user and was the first British-designed weapon to adopt the US practice of returning the weapon to the manufacturer for service.

The safety and arming systems on the WE.177 series (Permissive Action Links) were similar to those used on comparable American nuclear weapons but was a simple key operated Strike Enable Facility using a cylindrical barrel key similar to those used on gaming machines. The physical safety characteristics of WE.177 were probably comparable eg. using the concept of being 'one-point-safe' [http://www.osti.gov/opennet/document/guidline/pubgf.html#ZZ73] , plus the ability to activate its thermal batteries and fry the circuitry if it detected unauthorised interference, although there is no hard evidence or published sources that can positively confirm this.

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, 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 B models. Forty-three were deployed aboard Royal Navy surface vessels of frigate size and larger for use by embarked helicopters as an anti-submarine NDB starting in 1966. When the Navy's large aircraft carriers were decommissioned, twenty warheads were transferred to the RAF. The remaining weapons that were assigned to the Navy's helicopters were retired in 1992.

WE.177B

WE.177B weighed 457 kg (1007.5 lb), with a single yield of 450 kT. Although it weighed in excess of 1000 lb it was known in RAF Service as the "Bomb, Aircraft, 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 tactical role with these and other bombs. 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 single yield of 200 kT.

WE.177C was deployed only by RAF Germany in the tactical strike role, and used by Tornadoes and other strike aircraft. It was deployed probably from the early 1980s 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. One was to use the WE.177A NDB as a complete unit, as the standard issue in place of the Mk-44 or Mk.46 homing torpedo carried by the Ikara anti-submarine missile that armed some frigates of the Leander class. [PRO. AIR 2/13755 and others.] 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. Recently declassified archives disclose that the Ikara/WE.177A proposal received serious attention for some years, although there is no evidence of actual deployment.

Other proposals to re-engineer the WE.177A warhead into two submarine-launched heavyweight torpedoes also 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. [PRO. DEFE 24/389 E42] 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. [PRO. DEFE 24/389 E42] 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.

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" and RFA "Resource", 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 NDBs [PRO. DEFE 32/18 E25.3.e. Handwritten note in red ink in the margin states that "the NDB would be available for issue to approx forty (40) frigates in certain circumstances." (dated March 1969). Using that figure as a benchmark HMS "Hermes" and HMS "Invincible" together were likely to have a total of 26 WE.177A bombs aboard, and the RFA vessels were likely to have more based on MoD statements.] and there was concern at their possible loss in action, and at 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. [ [http://www.mod.uk/NR/rdonlyres/4625B8A4-C533-4DAD-9FA5-0BFEE58F8D69/0/op_corporate1982_nuclear_weapons.pdf Operation CORPORATE 1982 - Nuclear Weapons Task Force ] ]

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 at Kirtland Air Force Base in New Mexico, where it can be viewed alongside similar American weapons.

References

*Cocroft, W; Thomas, R. Cold War, "Building for Nuclear Confrontation 1946-1989", English Heritage, 2003. ISBN 1-873592-69-8, Outdated and accuracy now suspect.
* [http://nuclearweaponarchive.org/Uk/UKArsenalDev.html nuclearweaponarchive.org] - Outdated and accuracy now suspect.
*Moore, R; A Glossary of Nuclear Weapons, 'Prospero' Journal of the BROHP Spring 2004, a Visiting Fellow at the University of Southampton.
* [http://www.mcis.soton.ac.uk/Site_Files/pdf/nuclear_history/Working_Paper_No_1.pdf "The Real Meaning of the Words: a Pedantic Glossary of British Nuclear Weapons", Mountbatten Centre for International Studies, University of Southampton]
*Various declassified files available at The National Archives, London

Footnotes

ee also

*Nuclear weapons and the United Kingdom

External links

* [http://www.avrovulcan.org.uk/nukes/we177a_b.htm Photos of WE177 - #1]
* [http://www.century20war.co.uk/page5.html Photo of WE177 - #2]
* [http://www.skomer.u-net.com/projects/we177.htm Photo of WE177 - #3]
* [http://www.century20war.co.uk/page11.html Photo of WE177 after sled-testing in December 1965]
* [http://www.nuclear-weapons.info/vw.htm#WE.177 http://www.nuclear-weapons.info/vw.htm#WE.177]
* [http://www.bbc.co.uk/mediaselector/check/player/nol/newsid_7090000/newsid_7099100?redirect=7099125.stm&news=1&nbram=1&nbwm=1&bbram=1&bbwm=1 "The Dr. Strangelove scenario" - a BBC "Newsnight" report featuring the lack of a security features on the WE.177] (streaming video)
* [http://news.bbc.co.uk/1/hi/programmes/newsnight/7097101.stm A BBC "Newsnight" written commentary on the video above.]