In 1941, he joined the United States Merchant Marine, but he quickly tired of the long convoy runs, and in 1942, he moved to the United States Army, where he served as a paratrooper in the 501st Parachute Infantry Regiment, with the 101st Airborne Division in World War II. In 1944, on the eve of the D-Day invasion (in which many of his friends died), Warden, then a staff sergeant, shattered his leg when he landed in a tree during a night-time practice jump in England. He spent almost 8 months in the hospital recuperating, during which time he read a Clifford Odets play and decided to become an actor. Notably, Warden later portrayed a paratrooper from the 101st's rivals—the 82nd Airborne Division—in "That Kind of Woman".