Dec. 11 (UPI) -- Scientists determined the USS San Diego, which mysteriously sank during World War I, was attacked by a German U-Boat.
Navy researchers and oceanographers from the University of Delaware announced Tuesday that a landmine dispensed by the German ship resulted in the vessel becoming the only major U.S. warship to be lost in WWI and killing six enlisted soldiers.
Ken Nahshon of the Naval Surface Warfare Center said computer modeling showed the blast came from outside the ship, indicating it sunk as the result of an attack, rather than sabotage or an accident.
The ship sunk in 28 minutes after the exploding mine tore into a coal-filled storage hold as it traveled from from Portsmouth, N.H., to New York to join a convoy delivering troops and war material to France on July 19, 1918.
"The sinking happened in minutes, despite the precautions and the fact that underwater explosive attacks were rare at the time," said Nahshon.
German ships were known to frequent the area where the USS San Diego sank and the ship's captain had taken several precautions including stationing 17 sailors to watch for bubbles in the water that would indicate an oncoming torpedo.
Through reviewing transcripts and interviews, researchers found that no one onboard the ship mentioned seeing the bubbles, leading to the conclusion the ship was damaged by a mine.
"The captain did everything right," archaeologist Alexis Catsambis, one of the researchers in the report, said.
Researchers created a three-dimensional sonar model of the wreck, which indicated it was hit with a single explosion that left the ship unable to limit the amount of water rushing in.
The sea water flooded the boat's gun decks, causing the boat to list as hundreds of tons of more water reached the ships interior, causing it to sink.