In the U.S. Navy, Breault held the rank of Torpedoman’s Mate Second Class, and he sailed on U.S. Submarine O-5, which also had the identifying tag of SS-66. The U.S. Navy built 16 O-class submarines in time to join the First World War in 1918.
The O-class subs were 172 feet from stern to prow and were capable of diving to a depth of 200 feet. The craft were powered by two diesel engines each driving a single propeller shaft. The full complement for the submarine was 29 men, and they were armed with four torpedo tubes and an on-deck three-inch gun.
Construction of the U.S.S. O-5 started in December 1916 at the Fore River Shipbuilding Company in Quincy, Massachusetts, and she was ready for launch in November of the next year. She went into service in June 1918, with just five months of World War I remaining.