 His operational career began late in 1944 when he joined 182 Squadron, flying Hawker Typhoons on close support to the Allied armies in the Low Countries.After serving also with 181 Squadron, he was given command of 182 Squadron shortly before the end of the war.In 1947 Derry joined de Havilland as a test pilot, working largely on the de Havilland DH 108 aircraft.