Ordained in Rome Dec. 8, 1939, by Bishop Ralph Hayes of Davenport, Iowa, then rector of the North American College, Father Hannan remained in Rome until the following summer, when all American seminarians were ordered by the U.S. secretary of state to leave to ensure their personal safety. He celebrated his first Mass in the United States June 16, 1940, at St. Matthew Cathedral in Washington.
He then served as assistant pastor for two years at St. Thomas Aquinas Church in Baltimore.
In 1942, he volunteered as a wartime paratroop chaplain and served with the 505th Parachute Regiment of the 82nd Airborne Division. After cursory instructions on the ground, he took five practice jumps to earn his official status as a paratroop chaplain.
After his first jump, he was appointed “jump master” to a small crew of greenhorn jumpers and he affectionately became known as “The Jumping Padre.”