 During World War II, Bellah served in the United States Army, starting as a lieutenant in the 16th Infantry, was detailed to the General Staff Corps before Pearl Harbor, and was later assigned to Headquarters 1st Infantry Division, later with the 80th Infantry Division.Later he served on the staff of Admiral Lord Louis Mountbatten in Southeast Asia.He was attached to General Wingate's Chindits in combat in Burma, and to General Stillwell and to Colonel Cochran's 1st Air Commando Group.