The third USS Ontario (AT–13), a single screw seagoing tug, was laid down by the New York Shipbuilding Company, Camden, New Jersey on 23 November 1911, launched on 11 April 1912, and commissioned at Philadelphia Navy Yard on 4 September 1912.

On an unknown date she towed Schooner Charlotte W. Miller from near Bartletts Reef (near New London, Connecticut), where she had been sunk in a collision with USS D-2 on either 31 July 1917 to the vicinity of Sarahs Ledge in Long Island Sound where she sank again on 1 August.

[1] From 24 December 1917 to 2 January 1918, Ontario helped rescue grounded freighter Matanzas, an ammunition filled merchantman in danger of breaking up off Halifax, Nova Scotia and then returned to towing and netlaying duties.

The tugboat sailed for Queenstown, Ireland in late summer 1918, and joined the Atlantic Fleet Mine Force, patrolling off Daunt Rock Light Vessel, on guard against enemy submarines until after the Armistice.

For the next two decades, aside from regular yard periods at Pearl Harbor for repairs, Ontario operated out of the United States Naval Station Tutuila in her diverse but useful capacity, becoming a legend to Samoa's young men who were encouraged to join the Navy because of her presence.