On the evening of Friday, September 6, Churchill left 10 Downing Street for Chequers. After his customary nap, he dined with Pug Ismay, John Dill, and Alan Brooke, the senior officers most responsible for Britain’s defense. Their conversation focused on the danger that a German invasion was no longer theoretical but might be close at hand.

The discussion was driven by new intelligence. Intercepted signals and reconnaissance photographs suggested that concrete invasion preparations were advancing quickly: barges had multiplied at Ostend, more had appeared at Flushing, and additional vessels were gathering in Channel ports. The Joint Intelligence Committee also judged that September 8 through 10 would offer especially favorable moon and tide conditions for an amphibious landing, while heavy bombing attacks on Kent and the Thames Estuary added to the sense that Germany was softening targets before a move across the Channel.

As the evening continued, Churchill became animated and intellectually combative. Alan Brooke later recalled Churchill imaginatively placing himself in Hitler’s position and arguing through how he would attack Britain, then turning to revisions of the air-raid warning system and inviting criticism of his ideas. The meeting ran late into the night, showing both Churchill’s energy and the urgency of the moment.

By the next day, September 7, Brooke believed all reports pointed toward invasion drawing nearer. As commander in chief of Home Forces, Brooke felt an almost unbearable burden because Britain’s survival would depend on his preparations despite known weaknesses in training and equipment. He also believed he could not reveal his fears without damaging morale, so he carried his anxiety in private while he and the chiefs of staff weighed whether to issue the code word Cromwell, the official alert that invasion was imminent and mobilization must begin.