San Diego was launched on 28 April 1904 as armored cruiser California (Armored Cruiser No. 6) and was renamed on 1 September 1914. On 21 January 1915, San Diego suffered an explosion in her No. 1 fire room, killing five Sailors and injuring seven more. Ensign Robert Webster Cary, Jr. and Fireman Second Class Telesforo Trinidad received Medals of Honor for their actions during the fire to save their fellow crewmen.
Following America's entrance into World War I in April 1917, San Diego operated as the flagship for Rear Admiral William F. Fullam, commander of the Patrol Force U.S. Pacific Fleet, until she was reassigned to the U.S. Atlantic Fleet in July.
On 19 July 1918, while enroute from New Hampshire to New York, San Diego struck a German mine. Captain Harley H. Christy ordered the crew to abandon ship. Six Sailors out of the crew of 1,183 were lost when San Diego sunk off the coast of Fire Island, New York.
San Diego was the only major warship lost by the United States in World War I. The ship is historically significant in naval architecture and tactics and as a reminder of the close proximity of the enemy to U.S. shores during the war. Additionally, the wreck site is the final resting place for the six Sailors who lost their lives in the service of their country.
Naval History and Heritage Command manages the wreck site of San Diego as a sunken military craft, a war grave, and as part of the U.S. Navy’s overall cultural resource management program.