Armored Cruiser 6 was originally named the USS California, the ship that would later be renamed to the USS San Diego. She was laid down in 1902 and launched 28 April 1904 by the Union Iron Works, San Francisco, Calif.; sponsored by Miss F. Pardee; and commissioned 1 August 1907, with Captain V. L. Cottman in command. She was 503 feet long and had a beam of almost 70 feet. The ship weighed about 15,000 tons fully outfitted and loaded for duty and was powered by two coal burning, four cylinder, triple expansion steam engines, which drove her two 37,000 pound bronze/magnesium propellers and produced 25,000 horsepower.
She operated in the Pacific Ocean, visiting many ports including the Philippines, China, Japan, Hawaii, Peru, and Guam. In January of 1911, she was designated the flagship of the Pacific fleet. On September 1, 1914, she was renamed the USS San Diego. This was done as a result to make her original name available for assignment to a battleship, as directed by Congress. Shortly after her renaming, a boiler explosion kills nine of her crew during a full speed run in the Gulf of California, and places her in reduced commission through the summer of 1915. A summary of what occurred follows
On 21 January 1915 the San Diego suffered a boiler explosion. While taking the half hour readings of the steam pressure at every boiler, Ensign Robert Webester Cary Jr. had just read the steam and air pressure on number 2 boiler. He had just stepped through the electric watertight door into number 1 fire room when the boilers in number 2 fire room exploded. In fire room number 2 at the time was Second Class Fireman Telesforo Trinidad, of the Philippines and R. E. Daly, along with one other man. Ensign Cary stopped and held open the watertight doors which were being closed electrically from the bridge, and yelling to the men in No. 2 fire room to escape through these doors, which 3 of them did do. Ensign Cary held the doors open for a full minute with the escaping steam from the ruptured boilers around him. For His extraordinary heroism Ensign Cary was awarded the Congressional Medal of Honor. He would later retire with the rank of Rear Admiral. Fireman Telesforo Trinidad was driven out fire room No. 2 by the explosion, but at once returned and picked up R. E. Daly, Fireman Second Class, whom he saw injured, and proceeded to bring him out. While coming into No. 4 fire room, Trinidad was just in time to catch the explosion in No. 3 fire room, but without consideration of his own safety, passed Daly on and then assisted in rescuing another injured man from No. 3 fire room. Trinidad was himself burned about the face by the blast from the explosion in No. 3 fire room. For his extraordinary heroism Fireman Second Class Trinidad was awarded the Congressional Medal of Honor also for this incident.
The San Diego returned to duty as flagship through 12 February 1917, when she went into reserve status until the opening of World War I.
On April 6, 1917, California Governor William D. Stephens received a telegram from the Secretary of the Navy calling the State’s Naval Militia into Federal Service. Upon the Governor’s orders the Naval Militia was immediately directed to assemble at their Armories and prepare for muster. The following organizations were mustered in as National Naval Volunteers: First Division, San Francisco; Second Division, San Francisco; Third Division, San Diego; Fourth Division, Santa Cruz; Engineer Section, Fourth Division, Santa Cruz; Fifth Division, Eureka; Sixth Division, Santa Barbara; Seventh, Eight, and Ninth Divisions, Los Angeles; Aeronautic Section, Ninth Division, Los Angeles; Tenth Division, San Diego; Eleventh Division, Los Angeles; First Engineer Division, San Francisco; Second Engineer Division, Los Angeles; and the First Marine Company, Los Angeles. The entire organization was subsequently mobilized on board the USS Oregon, USS San Diego, USS Huntington and USS Frederich.
On April 15th Lieutenant Adolph B. Adams and his 5th Division, California Naval Militia left with the San Francisco and Santa Cruz Divisions for Mare Island. At Mare Island the Division reported to George W. Williams on the USS Oregon and were assigned to the Armored Cruiser USS San Diego. On April 17th, sixteen men of the division were transferred to the USS Frederich. Between May 31st and July 18th 1917 those of the Division that were aboard the USS San Diego participated in Convoy duty along the California coast. One mission was a trip from Honolulu, Hawaiian Territory to Port Townsend with an interned German vessel under convoy escort. These duties entitled all the members of the ship to the “Escort” bar for their World War I Victory Medals.
On 18 July, the USS San Diego was ordered to the Atlantic Fleet. Reaching Hampton Roads, Virginia on 4 August, she joined Cruiser Division 2, and later bore 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 escorts.
On 8 July 1918, the San Diego left Portsmouth, New Hampshire, en route to New York. She had rounded Nantucket Light and was heading west. On 19 July 1918, she was zigzagging as per war instructions on a course for New York. The Sea was smooth, and the visibility was 6 miles. At 11:23 AM, a huge explosion tore a large hole in her port side amidships. The explosion crippled the port engine. Captain Christy immediately sounded the submarine defense quarters, which involved a general alarm and closing of all watertight doors. Soon after two more explosions ripped through her hull. These secondary explosions were later determined to have been caused by the rupturing of one of her boilers and the ignition of one of her magazines. The ship immediately started to list to port. Captain Christy ordered the starboard engine rung up to full speed and headed toward the shore in an attempt to ground the San Diego in a salvageable depth of water. Soon afterward the starboard engine quit. The Officers and crew quickly went to their battle stations. Guns were fired from all sides of the warship at anything that could be a periscope or submarine. Her port guns fire until they were awash. Her starboard guns fired until the list of the ship pointed them into the sky. Under the impression that a submarine was in the area, the men stayed at their posts until Captain Christy gave the order “All hands abandon ship” after the starboard engine quit. At 11:51 AM the San Diego sunk only 28 minutes after the initial explosion. As per Navy tradition Captain Christy was the last man off the ship. As the Captain left the ship, the crew in the lifeboats gave him a cheer and burst in to signing the National Anthem. As the Officers and crew watched from their lifeboats the San Diego gently rolled over and was gone, along with six of her crew. It is amazing that 1,177 of the ship's crew and officers were able to abandon ship in a such a short time.
The German submarine U156 is credited with sinking the USS San Diego. The submarine laid mines in the area where the cruiser was lost. Unfortunately we will never know the details of the U156 operations, as the submarine was sunk on her return voyage after entering a mine field.
The USS San Diego (ACR 6) today lies upside down about eleven miles southeast of Fire Island inlet, Long Island, New York at Loran 26543.4 43693.2 in 115 feet of sea water.