Navy chaplain on board the aircraft carrier USS Franklin when it was
bombed by a Japanese plane in March 1945 (see plot summary for The Ship That Wouldn't Die (1945).
Received the Medal of Honor for his actions subsequent to the
bombing.
The USS O'Callahan, a U.S. Navy destroyer escort (DE-1051) later
reclassified as a frigate (FF-1051), was named in his honor.