David Dimbleby tells the story of the impassioned, often bitter, debate that raged in the United States over whether America should get involved in another European war. It ended the night the Japanese bombed Pearl Harbor, and Churchill, as he put it, 'slept the sleep of the saved'.

Tonight's programme shows how the Cold War gave Britain a new role in the alliance, as an essential forward base for American bombers; but how her own freedom of action was limited - a truth brutally exposed by the Suez crisis of 1956. As the British launched their invasion, President Eisenhower rang Prime Minister Eden. 'I can only presume you have gone out of your mind', he said.