Delaforce served as an artillery officer in the 13th Regiment, Royal Horse Artillery (Honourable Artillery Company) during World War II. He participated in Operation Overlord, Operation Market Garden, and the Liberation of Belgium from 1944 to 1945. In the Netherlands, he became a forward observation officer, and was injured, having his ribs and one arm broken, and his leg paralysed when his Universal Carrier was hit by an anti-tank mine. He rejoined his unit once he recovered in November 1944, and received his first of two mentions in dispatches for successfully deterring a German Tiger tank during battle along the river Elbe with only a Sten when his unit's anti-tank guns had all been destroyed. During the battle, he was hit by a grenade, his second injury of the war. His second mention of dispatch came at a later date, when he directed artillery fire while in close proximity to the enemy.