For the remainder of the Second World War, Brooke was the foremost military adviser to the British Prime Minister, Winston Churchill (who was also Minister of Defence), the War Cabinet, and to Britain's allies. As CIGS, Brooke was the functional head of the British Army, and as chairman of the Chiefs of Staff Committee, which he dominated by force of intellect and personality, he took the leading military part in the overall strategic direction of the British war effort. In 1942, Brooke joined the Western Allies' ultimate command, the U.S.-British Combined Chiefs of Staff.