The explosion of an atomic bomb in the New Mexico desert in July 1945 showed that the Allies had beaten the Nazis in the first lap of a race to develop the ultimate weapon. The first bombs were so bulky they needed a massive bomber to deliver them; today, the Tomahawk cruise missile is barely larger than a torpedo and can carry a far more powerful weapon hundreds of miles. This programme looks at the weapons race which continued with the Soviet Union using every means possible – particularly espionage - to catch up with the United States, and then competing to produce smaller and more deadly bombs. Today, the race has entered a new phase – with the threat of nuclear weapons falling into the hands of unstable regimes or terrorists determined to use them.