Mariner, formerly the steam tug Jack T. Scully of the Neptune Line, New York City, was built in 1899 by A. C. Brown, Tottenville, Staten Island, New York and had previously steamed between New York and Bangor, Maine. Considered “strongly built” and a “good sea boat” for potential employment as a minesweeper, Mariner was delivered to the Navy on 25 September 1917. Earmarked “for distant service” on 1 October 1917 and given the designation SP-1136, she was commissioned at the New York Navy Yard, Brooklyn, New York, on 19 December 1917, Lt. (jg.) Martin Miller, USNRF in command. The Navy spent $3,000 refitting the tug for naval service.