The U.S. Navy believes it has solved the mystery of what doomed the USS San Diego just miles from New York City during World War I.
Researchers have determined that it was an underwater mine set by a German submarine, not sabotage or a torpedo.
The San Diego was sailing to New York on July 19, 1918, when an external explosion near the engine room shook the armored cruiser. The vessel sank in less than a half hour. Six crew members died.
German naval records recovered after the war revealed that U-boat 156 had sailed just off the coast of New York, planting explosives.
The U.S. Naval History and Heritage Command asked scientists, archaeologists and historians to investigate. The findings were presented this week at a science conference.