Upon graduation, Carpenter was commissioned as an infantry officer and went on to serve at least two tours in Vietnam. In 1964, he was an adviser assigned to an airborne brigade of the Army of the Republic of Vietnam. That unit came under heavy enemy fire immediately after being inserted by helicopter into a sugar cane field. Bill Carpenter was wounded by a gunshot through the arm while changing rifle magazines. His radio set was hit with another bullet and he was spun around and knocked to the ground. He proceeded to eliminate the source of the enemy fire, by knocking out a bunker with a hand grenade. For his actions he was awarded the Silver Star, the U.S. Army's third highest award for valor in combat.