Nixon served during World War II. He was selected (inducted) into the United States Army on January 14, 1941, in Trenton, New Jersey. After graduating from Army Officer Candidate School in 1941 as an infantry second lieutenant, he volunteered for the parachute infantry, part of the U.S. Army's fledgling airborne forces. He was assigned to E Company, 2nd Battalion, 506th Parachute Infantry Regiment (506th PIR), commanded by Colonel Robert Sink. The 506th was an independent regiment until June 1943, when it became part of the 101st Airborne Division. He went through the regimental unit training and pre-airborne training at Camp Toccoa, Georgia, and Airborne School at Fort Benning, eventually training at many locations throughout the United States. In September 1943, he was sent with the 506th to Aldbourne, Wiltshire, England, in preparation for the Allied invasion of Normandy.