UK Trident programme

The UK Trident programme encompasses the development, procurement and operation of the current generation of British nuclear weapons, and the means to deliver them.

Trident itself 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 reentry vehicles (MIRVs). It is the most expensive and the most powerful capability of the British military forces.

Operated by the Royal Navy and based at Clyde Naval Base on Scotland's west coast, at least one submarine is always on patrol to provide a continuous at-sea capability. Under the terms of the 2010 Strategic Defence and Security Review, each will be armed with a maximum of eight missiles and 40 warheads, although their capacity is much larger.

The UK Trident programme was announced in July 1980, and patrols began in December 1994. Since 1998, Trident has been the only British nuclear weapon system in service. Its stated purpose is to provide "the minimum effective nuclear deterrent as the ultimate means to deter the most extreme threat."