When Churchill returned to the Admiralty in September 1939 he set up an experiment in the basement code-named ‘White Rabbit Number Six’. The aim was to construct a model of a giant machine that would cut a deep groove in the earth, along which soldiers could safely advance towards the enemy in the battles expected on the western front. Throughout the Phoney War Churchill pursued the idea with great excitement, demanding that scarce resources be diverted for the purpose. When France capitulated the project had to be mothballed, but the pursuit of technological wonders continued to be one of the most striking characteristics of his war leadership. Yet as Graham Farmelo remarks, the most revolutionary development of the war years – the making of the atom bomb – failed to capture his imagination.