The dropping of nuclear bombs on Nagasaki and Hiroshima in 1945 changed the world forever - any nation that failed to harness the power of the atomic bomb suddenly seemed extremely vulnerable.
The concept of Mutually Assured Destruction - or 'MAD' - dictates that if two warring nations have access to nuclear weapons, then it would be folly for either side to use them - as the inevitable retaliation to a nuclear strike is, of course, a nuclear strike.
So it was that Britain needed to become a nuclear power, and the Hydrogen Bomb - or H-bomb - provided the ultimate destructive force.
