The Trident nuclear missile was born in the United States as a sixth generation member of the U.S. Navy's Ballistic Missile Fleet program that began in 1956. Developed and manufactured by Lockheed Martin, Trident's name is derived from the mythical three-pronged spear used for fishing by Neptune and Poseidon.
Trident I missiles were first fitted to American submarines in 1979 and then in 1986, installed in Britain's Vanguard craft which were designed to hold and launch Trident II D5 missiles.
The UK's current Trident missiles weigh 130,000lbs (58,500kg), are 44ft (13m) tall and have a 74 inch (1.9m) diameter. Possessing immense power, speed and accuracy, the Trident II missiles have a range of 4,600 miles (7,400km), travel at 20,000ft (6,100 metres) a second and arrive within three feet of their target. They don't come cheap however. Each of the 16 Trident II missiles carried aboard Vanguard submarines cost £16.8m ($29.1m).
The missiles - part of Britain's 'independent' nuclear deterrent - must be serviced periodically across the Atlantic at the Strategic Weapons facility in Georgia.
Although each Trident missile is capable of carrying 12 warheads, the 1998 Strategic Defence Review limited the number of warheads allowed on a single submarine to 48. Many people want Trident abolished entirely and are against the government paying up to 20 billion per year for 30 years to keep it alive, saying the nuclear weapons have no place in modern, post-Cold War society. There's also the question of whether revamping Trident violates the Nuclear Non-Proliferation Treaty in which nations, including the UK, agreed to cease their nuclear production, not increase it.
Tony Blair says that the treaty doesn't commit countries to complete disarmament, and claims the UK has already reduced nuclear weapons by 70 percent since the Cold War. Blair has proposed the possibility of further reducing the number of submarines and warheads, but he strongly believes that keeping Trident is imperative in an unstable world.