USS California ( ACR - 6 ) The second USS " California " ( ACR - 6 ) , also referred to as " Armored Cruiser 6 " , and later renamed San Diego , was a United States Navy armored cruiser . She was launched on 28 April 1904 by Union Iron Works , San Francisco , California , sponsored by Miss Florence Pardee ( daughter of California governor George C . Pardee ) , and commissioned on 1 August 1907 , Captain V . L . Cottman in command . Joining the 2nd Division , Pacific Fleet , " California " took part in the Naval Review at San Francisco in May 1908 for the Secretary of the Navy Victor H . Metcalf . Aside from a cruise to Hawaii and Samoa in the fall of 1909 , the cruiser operated along the west coast , sharpening her readiness through training exercises and drills , until December 1911 , when she sailed for Honolulu , and in March 1912 continued westward for duty on the Asiatic Station . After this service representing American power and prestige in the Far East , she returned home in August 1912 , and was ordered to Corinto , Nicaragua , then embroiled in internal political disturbance . Here she protected American lives and property , then resumed her operations along the west coast ; she cruised off California , and kept a watchful eye on Mexico , at that time also suffering political disturbance . During that time in Mexico , she was involved in an international incident in which two of her crew were shot and killed . Conversion to USS San Diego . " California " was renamed San Diego - - - in order to free up her original name for use with the " Tennessee " - class battleship - - - on 1 September 1914 , and served as flagship for Commander - in - Chief , Pacific Fleet , intermittently until a boiler explosion put her in Mare Island Navy Yard in reduced commission through the summer of 1915 . The boiler explosion occurred in January 1915 and the actions of Ensign Cary and Fireman Second Class Trinidad during the event earned them both the Medal of Honor . " San Diego " returned to duty as flagship until 12 February 1917 , when she went into reserve status until the opening of World War I . Placed in full commission on 7 April , the cruiser operated as flagship for Commander , Patrol Force Pacific Fleet , until 18 July , when she was ordered to the Atlantic Fleet . Reaching Hampton Roads on 4 August , she joined Cruiser Division 2 , and later broke the flag of Commander , Cruiser Force , Atlantic , which she flew until 19 September . " San Diego " s essential mission was the escort of convoys through the first dangerous leg of their passages to Europe . Based on Tompkinsville , New York , and Halifax , Nova Scotia , she operated in the weather - torn , submarine - infested North Atlantic safely convoying all of her charges to the ocean escort . Loss . Early on 19 July 1918 , " San Diego " left the Portsmouth Naval Shipyard bound for New York where she was to meet and escort a convoy bound for France . Her captain — Harley H . Christy — ordered a zigzag course at a speed of . Visibility was reported as being from . In his report to a Board of Inquiry on the cruiser ' s loss , Christy stated that all lookouts , gun watches , and fire control parties were at their appointed stations and on full alert , and that all necessary orders to safeguard the watertight integrity of the ship in dangerous waters had been given and were being carried out . At 11 : 05 the next day , 19 July , " San Diego " was steaming northeast of the Fire Island Lightship when an explosion occurred on the cruiser ' s port side adjacent to the port engine room and well below the waterline . The bulkhead at the site of the explosion was warped so that the watertight hatch between the engineroom and No . 8 fireroom could not be shut , and both compartments immediately flooded . Captain Christy assumed that the ship had been torpedoed and immediately sounded submarine defense quarters and ordered all guns to open fire on anything resembling a periscope . He called for full speed ahead on both engines and hard right rudder , but was told that both engines were out of commission and that the machinery compartments were rapidly flooding . The ship had taken on a 9° list and water began pouring in through one of the gun ports , flooding the gun deck . Informed that the ship ' s radio was not working , Christy despatched the gunnery officer to the mainland with a boat crew to summon rescue vessels . About 10 minutes after the explosion , the cruiser began to sink . Orders were given to lower the liferafts and boats . Captain Christy held off giving the order to abandon ship until he was certain that " San Diego " was going to capsize , when the crew abandoned the vessel in a disciplined and orderly manner . Christy was the last man to leave the ship . She had sunk in 28 minutes with the loss of six lives , the only major warship lost by the United States in World War I . Two men were killed instantly when the explosion occurred , a crewman who had been oiling the port propeller shaft was never seen again , a man was killed by one of the smokestacks breaking loose as the ship capsized , one was killed when a liferaft fell on his head , and the sixth was trapped inside the crow ' s nest and drowned . Meanwhile , the gunnery officer had reached shore at Point O ' Woods , New York after a two - hour trip , and vessels were at once sent to the scene . The Navy Department was informed that a German minelaying submarine was operating off the east coast of the US and the US Naval Air Service was put on alert . Aircraft of the First Yale Unit , based at Bay Shore , Long Island , attacked what they thought was a submerged submarine lying on the seabed in around and dropped several bombs ; it turned out to be " San Diego " . Cause . Captain Christy was of the opinion , following the sinking , that " San Diego " had been sunk by a torpedo . However , there was no evidence of a U - boat in the area at the time , and no wake of a torpedo was seen by the lookouts . While it was reported that five or six mines had been found in the area , the idea that she had struck a mine was also considered unlikely as it was thought that a mine would have been more likely to detonate at the bow or the forward part of the ship . It was subsequently reported that experienced merchant officers believed that a mine was the probable cause , due to the violence of the explosion and the rapidity with which the ship sank . In August , the Naval Court of Inquiry appointed to investigate the loss of the cruiser concluded that " San Diego " had been sunk by a mine , mentioning that six contact mines had been located by naval forces in the vicinity of the spot where she had sunk . The German submarine had earlier laid a number of mines along the south shore of Long Island , and the sinking of " San Diego " was attributed to her . Wreck . The wreck presently lies in of water , with the highest parts just below the surface , and as a result is one of the most popular shipwrecks in the US for scuba diving . Unfortunately the wreck lies inverted ( upside - down ) and has decayed over the last century . More SCUBA divers have died over the years on the wreck than the number of crew killed in its sinking , but this has not diminished its popularity . Nicknamed the " Lobster Hotel " for the abundance of lobsters living there , it is also a home to many kinds of fish . The wreck lies at N40° 33 ' 00 . 36 " , W073° 00 ' 28 . 39 " , approximately due south of the intersection of Route 112 and Montauk Highway in Patchogue , New York . The wreck is listed in the National Register of Historic Places .