McElroy began his military service during the First World War where he was a surviving crew member of the SS Gulflight, torpedoed by an Imperial German U-Boat 22 nautical miles off the coast of the Isles of Scilly. It was the first American ship to be torpedoed in the Great War, the beginning of unrestricted submarine warfare. The attack occurred only days before the sinking of the RMS Lusitania.

After Navy discharge, McElroy sailed as officer in merchant vessels for 10 years, qualifying in 1928 for a Master Mariner’s Papers as well as a commission as a reserve lieutenant and admission to Harvard College.

McElroy commanded the Naval and Marine Corps Reserve Training Center in San Francisco–one of the largest in the nation. It then trained over 21,000 reservists.

McElroy graduated from Harvard University in 1932 with a degree in history. Naval and Marine history has become the Admiral’s avocation.

He was one of the organizers and planners of Adm. S.E. Morigon’s Harvard Columbus Expedition of 1939-40 and served as navigator of the Expedition and Master of the Barkentine Capitana. The ship traced Christopher Columbus’ four voyages to the New World.

McElroy Commanded the attack transport Maraton during the assault on Okinawa. In 1945, he assisted in the planning and landings of amphibious forces at Wakayama, Japan. At the outbreak of Korean hostilities, he took command of the Consolation, first navy ship to be equipped with a helicopter landing deck. Besides saving lives of countless American fighting men, on Christmas Day 1951, the ship saved 16 men, women and children in a small Korean ship which had parted her anchor cables in rough seas of the Korean Coast.