(Submarine # 68) Rear view of O-7's 3/23 retractable deck gun in the raised position, circa 1918-1919. Note the gun's vertical block breech mechanism, round hatch shield, and ready-service ammunition attached to the base of the gun mount. Collection of Christopher H.W. Lloyd. Donated by Virginia Agostini, 1990. U.S. Naval History and Heritage Command Photograph.