page_title: Trident (UK nuclear programme)
section_title: Warheads
hierarchical_section_title: Trident (UK nuclear programme) / Design, development and construction / Warheads
caption_attribution_description: English: Models of the cone-shaped warheads on a Trident missile at the National Museum of Nuclear Science &amp; History in New Mexico, United States.
context_page_description: Trident, also known as the Trident nuclear programme or Trident nuclear deterrent, covers the development, procurement and operation of nuclear weapons in the United Kingdom and their means of delivery. Its purpose as stated by the Ministry of Defence is to "deter the most extreme threats to our national security and way of life, which cannot be done by other means". Trident is an operational system of four Vanguard-class submarines armed with Trident II D-5 ballistic missiles, able to deliver thermonuclear warheads from multiple independently targetable re-entry vehicles. It is operated by the Royal Navy and based at Clyde Naval Base on the west coast of Scotland. At least one submarine is always on patrol to provide a continuous at-sea capability. Each one carries up to eight missiles and forty warheads, although their capacity is higher. The missiles are manufactured in the United States, while the warheads are British.
  The British government initially negotiated with the Carter administration for the purchase of the Trident I C-4 missile. In 1981, the Reagan administration announced its decision to upgrade its Trident to the new Trident II D-5 missile.
context_section_description: Under the 1958 US–UK Mutual Defence Agreement the UK is allowed to draw upon US warhead design information, but constructing and maintaining warheads for the Trident programme is the responsibility of AWE. The exact number of warheads carried on patrol at any given time is classified information. An article by the Federation of American Scientists argued that British nuclear warhead is based on the US W76 warhead engineering design, a conclusion that the Defence Select Committee concurred with in 2006. The National Audit Office recorded in 1987 that most of the warhead development and production expenditure was planned to be incurred in the US. Additionally, much of the nuclear materials for the warheads was purchased from the US on cost grounds. US President George H. W. Bush authorised the transfer of nuclear warhead components to the UK between 1991 and 1996.
  In British service, Trident II missiles are fitted with a thermonuclear warhead called Holbrook. The warhead is of variable yield design and is estimated to have a maximum yield of 100 kilotons of TNT (420 TJ), with lower yields in the range of 0.3 kilotons of TNT (1.3 TJ) and 5 kilotons of TNT (21 TJ) to 10 kilotons of TNT (42 TJ) Each warhead is housed in a cone-shaped re-entry vehicle made in the United States. This shell protects it from the high temperatures experienced upon re-entry into Earth's atmosphere. The Trident warhead's fusing, arming and firing mechanisms are carefully designed so that it can only detonate after launch and ballistic deployment. Conservative governments were sensitive to charges that the replacement of Polaris with Trident would involve an escalation in the numbers of British nuclear weapons. When the decision to purchase Trident II was announced in 1982, it was stressed that while American Trident boats carried 24 missiles with eight warheads each, a total of 192 warheads, British Trident boats would carry no more than 128 warheads—the same number as Polaris. In November 1993, the Secretary of State for Defence, Malcolm Rifkind, announced that each boat would deploy no more than 96 warheads.  In 2010 this was reduced to a maximum of 40 warheads, split between eight missiles. The consequent reduction in warhead production and refurbishment was estimated to save £22 million over a ten-year period.
  The warheads are primarily constructed at AWE Aldermaston, on the site of former RAF Aldermaston, with other parts being made at other AWE facilities such as in Burghfield. The British government insists the warhead is indigenously designed, but analysts including Hans M. Kristensen with the Federation of American Scientists believe that it is largely based on the US W76 design. Under the 1958 US–UK Mutual Defence Agreement the UK is allowed to draw upon US warhead design information, but constructing and maintaining warheads for the Trident programme is the responsibility of AWE. The first Holbrook warhead was finished in September 1992 with production probably ending in 1999. Each warhead is housed in a cone-shaped re-entry vehicle made in the United States called the Mk 4 and is the same reentry vehicle used by the US Navy with its W76 warhead. This shell protects it from the high temperatures experienced upon re-entry into Earth's atmosphere. The Trident warhead's fusing, arming and firing mechanisms are carefully designed so that it can only detonate after launch and ballistic deployment.
  On 25 February 2020, the UK released a Written Statement outlining that the current UK nuclear warheads will be replaced and will match the US Trident SLBM and related systems. Earlier, it was reported that Commander US Strategic Command, Admiral Charles Richard, mentioned in a Senate hearing that the UK was already working to replace its warheads, matching the future US W93 warhead.
  As of 2016, the UK had a stockpile of 215 warheads, of which 120 were on operational deployment on submarines. The 2010 Strategic Defence and Security Review reduced the number of warheads and missiles for the ballistic missile submarine on patrol to 40 and 8 respectivel
caption: Models of the black warhead re-entry vehicles on a Trident missile at the National Museum of Nuclear Science & History in New Mexico
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