Beahan attended Rice University on a football scholarship during the 1930s. In 1939 he joined the Army Air Forces as an aviation cadet but washed out of pilot training, becoming a bombardier instead. He was assigned to the 97th Bombardment Group and took part in the first B-17 raids in Europe by Boeing B-17 Flying Fortresses. He flew 13 missions over Europe, 17 missions over North Africa, and five credited combat missions in the Pacific with the 509th Composite Group (including the Nagasaki sortie). He was shot down and crash-landed four times (twice in Europe and North Africa).
