(SS63: dp. 520.6 (surf. n.), 629 (subm.); l 1724; b. 18 Ό; dr. 145; s. 14 k. (surf.), 10.5 k. (subm.); cpl. 29; a. 1 3, 4 18 tt.; cl. O1).
O2 was laid down 27 July 1917 by the Puget Sound Navy Yard; launched 24 May 1918; and commissioned at Puget Sound 19 October 1918, Lt. Comdr. F. T. Chew, in command.
During World War I, O2 patrolled off the New England coast until wars end. Reclassified as a second line submarine 25 July 1924, and reverting to a first liner 6 June 1928, she served at the submarine base, New London in training officers and men until 1931, except for a brief tour at Coco Solo, Panama in 1924. In 1931, she transferred to Philadelphia, where she decommissioned 25 June 1931.
With increasing possibility of U.S. involvement in World War II, O2 recommissioned at Philadelphia 3 February 1941. Steaming to New London in June, she trained submarine crews there until after Germany collapsed. She decommissioned 26 July 1945, was struck 11 August 1945, and was sold 16 November 1945.