When Williams joined the army, he was assigned to the Royal Corps of Signals, which was a typical assignment for university undergraduates. He received initial training in military communications, but was reassigned to artillery and anti-tank weapons. He was chosen to serve as an officer in the Anti-Tank Regiment of the Guards Armoured Division in 1941–1945, being sent into early fighting in the Invasion of Normandy after the D-Day Normandy Landings. He writes in "Politics and Letters", "I don't think the intricate chaos of that Normandy fighting has ever been recorded." He commanded a unit of four tanks and mentions losing touch with two of them while fighting against Waffen-SS Panzer forces in the Bocage. He never discovered what happened to them as a withdrawal of troops ensued.