A Sonoma-class tugboat, USS Ontario was laid down by the New York Shipbuilding Company, Camden, New Jersey on November 23, 1911; she was launched on April 11, 1912, and commissioned at Philadelphia Navy Yard on September 4, 1912 with Chief Boatswain S.M. McCarthy in command.
USS Ontario was decommissioned on June 3, 1946 and struck from the Naval Vessel Register on June 19, 1946. On April 4, 1947, she was sold to Floyd Harrington, Wilmington, California. She received one battle star for her service in World War II.
When the United States entered World War I in April 1917, she steamed along the East Coast laying anti-submarine nets and patrolling against minefields from Portsmouth, Virginia, to Portsmouth, New Hampshire and towed barges of essential war supplies to New England ports. From December 24 1917 to January 2 1918, Ontario assisted in the rescue of the grounded freighter Matanzas and then returned to towing and netlaying duties.
On January 3, 1941, she sailed for Pearl Harbor and remained there for the rest of the year; When the Japanese attacked Pearl Harbor on December 7, 1941, she shot down one enemy plane with her two machine guns.