Fifty years ago this week the idea of mutually assured nuclear destruction was outlined in a major speech. But how did this frightening concept of the Cold War fade from people's psyches?

Today the notion of all-out nuclear war is rarely discussed. There are concerns about Iran and North Korea's nuclear programmes and fears that terrorists might get hold of the technology and detonate a "dirty" nuclear bomb.

But the fear of a war in which the aim is to wipe out the entire population of an enemy has startlingly diminished.

In 1962, the concept of mutually assured destruction started to play a major part in the defence policy of the US. President Kennedy's Secretary of Defense, Robert McNamara, set out in a speech to the American Bar Foundation a theory of flexible nuclear response.

In essence it meant stockpiling a huge nuclear arsenal. In the event of a Soviet attack the US would have enough nuclear firepower to survive a first wave of nuclear strikes and strike back. The response would be so massive that the enemy would suffer "assured destruction".

Thus the true philosophy of nuclear deterrence was established. If the other side knew that initiating a nuclear strike would also inevitably lead to their own destruction, they would be irrational to press the button....