Trident: How did the UK develop its nuclear weapons programme?

In 1941, the then-Prime Minister Winston Churchill authorised the development of an atomic bomb after a report showed it was achievable.

However, the UK got off to a slow start with Churchill eventually reaching an agreement with US President Franklin Roosevelt to join the US' top secret Manhattan Project.

Taking place in New Mexico, the project also saw Canada take part, but in 1946 the collaboration was brought to an end with the UK deciding to pursue an independent programme.

This led to the UK successfully testing its first Atomic Bomb in 1952 – the same time the US was testing its thermonuclear hydrogen bomb (H-Bomb).

Following the US, the Soviet Union started working on its own H-Bomb in 1954.

In 1956, the UK had its first operational nuclear weapon – the Blue Danube free-fall bomb.

This was carried by the RAF's fleet of V-Bombers, made up of the Valiant, Victor and Vulcan aircraft.

The UK began development on a thermonuclear weapon and, in 1957 and 1958, carried out the first detonation of an H-Bomb in Malden and Christmas Islands, located in the Pacific Ocean.

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However, the UK's nuclear weapon development was about to undergo a radical change.

Due to concerns about the V-Bombers' vulnerability to Soviet air defences, the UK started to develop a ground-launched, silo-based missile system called Blue Streak.

This was cancelled in 1960 due to concerns about any potential pre-emptive strikes on the missile silos.

Based solely on the V-Bomber force, the UK was left with a nuclear weapons capability lacking credibility.

But, in 1962, then Prime Minister Harold Macmillan and President John F Kennedy signed the Nassau Agreement, giving the UK access to the Polaris missile system.

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A submarine-based system, Polaris entered service in 1968, with the V-Bombers stepping down from their nuclear role in 1969.

For 11 years, Polaris remained the UK's nuclear deterrent but, in 1980, the UK procured the Trident missile system from the US.

Still the UK's nuclear deterrent today, Trident is housed in four Vanguard-class submarines built in 1994, with Polaris eventually taken out of service in 1996.

Most recently, the UK Government announced the next generation of nuclear submarines in 2016.

The Dreadnought class of subs can produce their own oxygen and water, measure 153m in length and are expected to enter service in the 2030s.