He soon volunteered to go back to the front. He was promoted to captain, when his elder brother Peter, also an officer in the East Surrey Regiment, arrived in France in December 1916. At the time, Ackerley was his superior officer. He later wrote that the cheerful Peter saluted his brother "gladly and conscientiously." In February 1917, Peter was wounded in action on a dangerous assignment. Though Peter got back to the British lines, Ackerley never saw him again, as he was killed on 7 August 1918, two months before the end of the war. Peter's death haunted Ackerley all his life; he suffered from survivor's guilt.