|Ordered:||3 March 1916|
|Laid down:||27 July 1917|
|Launched:||24 May 1918|
|Commissioned:||19 October 1918|
|Decommissioned:||26 July 1945|
|Fate:||sold for scrap|
|Stricken:||11 August 1945|
|Displacement:||520.6 tons surfaced, 629 tons submerged|
|Length:||172 feet 4 inches|
|Draft:||14 feet 5 inches|
|Speed:||14 knots surfaced, 10.5 knots submerged|
|Complement:||two officers, 27 men|
|Armament:||one three-inch/50-caliber (76mm/50) gun; four 18-inch (457mm) torpedo tubes, eight torpedoes|
During World War I, O-2 patrolled off the New England coast until war's 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, Connecticut, in training officers and men until 1931, except for a brief tour at Coco Solo, Panama Canal Zone, in 1924. In 1931, she transferred to Philadelphia, Pennsylvania, where she decommissioned 25 June 1931.
With increasing possibility of U.S. involvement in World War II, O-2 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.