Walker later attended and graduated from the Royal Military College, Sandhurst, and was commissioned as a second lieutenant into the Royal Scots Greys on 16 April 1944. The salute at his commissioning parade was taken by American General Dwight D. Eisenhower, the Supreme Allied Commander for the upcoming Allied invasion of Normandy. Walker went on to command a Sherman tank and to participate in the Battle of the Reichswald with the 4th Armoured Brigade. He left the Army in 1946, having attained the rank of captain.