HMS Vengeance, one of Britain's four Vanguard-class ballistic missile submarines.

The United Kingdom became the latest nuclear weapon state to join the movement towards greater nuclear transparency on Wednesday when Foreign Secretary William Hague informed the British House of Commons that the U.K.’s “overall stockpile of nuclear warheads will not exceed 225 warheads” (“Britain Reveals Nuclear Arsenal: 225 Warheads,” New York Times, 26 May 2010). The Foreign Office subsequently confirmed that 225 is the number of nuclear weapons that the U.K. currently possesses.

Since  the retirement of Britain’s “tactical” nuclear weapons following the end of the Cold War, all British nuclear weapons are mounted on Trident II missiles leased from the United States. The missiles are deployed on Britain’s fleet of four Vanguard-class ballistic missile submarines. Each submarine carries 16 Trident II missiles, and each missile carries up to three nuclear warheads. Only three of the submarines are in service (one of which is at sea) at any time, however, with the other in overhaul.

Earlier in May, the United States disclosed the size of its nuclear stockpile, although that disclosure was incomplete in that it did not include some 4500 weapons awaiting dismantlement.

France has also taken steps towards greater transparency, specifying in 2008 that its arsenal would be reduced to fewer than 300 warheads.

Further commentary

Hans M. Kristensen, “Britain Discloses Size of Nuclear Stockpile: Who’s Next?” FAS Strategic Security Blog, 26 May 2010