Brother of 1395 Private Emerson Castle.
David Castle was with 9th Battalion reinforcements at Lemnos in reserve for Gallipoli but they were not deployed. In Egypt in January 1916 he transferred to the newly-raised 49th Battalion. He landed in France in June with his new unit which fought its first major battle at Mouquet Farm in August. In March 1917 he was hospitalised with influenza and trench feet. He re-joined his unit in May and five weeks later was killed in action at Messines, Belgium, aged 21. He was buried nearby but after the war his grave could not be found.