|Ordered:||3 March 1916|
|Laid down:||6 December 1916|
|Launched:||25 November 1917|
|Commissioned:||12 June 1918|
|Decommissioned:||11 September 1945|
|Fate:||sold for scrap|
|Stricken:||11 September 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 the final months of World War I, O-6 operated out of Philadelphia, Pennsylvania, on coastal patrol against U-boats, cruising from Cape Cod to Key West, Florida. A British merchantman fired six shots at O-6 on 14 July 1918, but caused no appreciable damage. On 2 November, the boat departed Newport in a 20-sub contingent bound for service in European waters, however, the Armistice with Germany had been signed before the vessels reached the Azores, and they returned to the United States.
After the war, O-6 prolonged her Naval career by operating as a training ship out of New London, Connecticut. Reclassified to a second line submarine 25 July 1924 while stationed at Coco Solo in the Panama Canal Zone, she reverted to first line class 6 June 1928 and continued at New London until February 1929, when she steamed to Philadelphia, Pennsylvania, to decommission there 9 June 1931.
Submarines had proved to be a major weapon in World War I. As U.S. involvement in World War II approached, old subs were taken out of mothballs and prepared to renew training activities. O-6 recommissioned at Philadelphia 4 February 1941 and then returned to New London to train students at the sub school. On 19 June 1941, O-6 made a trial run to Portsmouth, New Hampshire; the next day O-9 (SS-70) went down 15 miles off Portsmouth. O-6 joined O-10 (SS-71), Triton (SS-201), and other vessels in the search for the lost sub, but to no avail.
Remaining in the Portsmouth area, O-6 decommissioned there 11 September 1945, was struck from the Naval Vessel Register the same day, and was sold to John J. Duane Company of Quincy 4 September 1946. The boat was subsequently scrapped in December 1946.