As a commander of the British II Corps knew Brooke in 1940 by rear guard battles a significant contribution to the evacuation of the British army from Dunkirk.Later in 1940, Brooke appointed commander-in-Chief of the British army at home. He was given the difficult task the British defence against the expected German invasion to set up. End 1941 followed Brooke John Dill as Chief of the British general staff. In June 1942 Brooke became Chief of the Imperial General Staff where he the military ideas of Winston Churchill had to realize or the plans that were not feasible, had to talk out of his head.
He received many awards including the u.s. Army Distinguished Service Medal.