Mystery behind WWI shipwreck possibly solved during incredible exploration

The USS San Diego was the only major warship the U.S. lost during World War I. Now, nearly 100 years after it sank, and countless theories as to what caused the wreck, researchers believe they have determined the cause of it — a German U-boat in conjunction with a mine.

Presenting the theory at the American Geophysical Union’s (AGU) fall meeting, Dr. Alexis Catsambis said new survey data – based on additional research into archives, computer impact, flood models and surveying the area of the ocean floor where it lays – all point toward the Germans.

“The legacy of the incident is that six men lost their lives on July 18, 1918,” said Catsambis in a statement obtained by Fox News. “With this project we had an opportunity to set the story straight and by doing so, honor their memory and also validate the fact that the men onboard did everything right in the lead up to the attack as well as in the response. The fact that we lost six men out of upwards of 1100 is a testament to how well they responded to the attack.”

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The 500-foot armored cruiser, which had 1,177 crewmembers, sank approximately 8 miles from Fire Island, New York, in just 28 minutes. It is believed the German U-boat U-156 was responsible for the sinking.

The USS San Diego still resides largely intact in approximately 115 feet of water, albeit upside down, Live Science reports.

USS San Diego on Jan. 28, 1915, while serving as flagship of the Pacific Fleet. Her name had been changed from California on Sept. 1, 1914. Note two-star Rear Admiral's flag flying from her mainmast top. U.S. Naval History and Heritage Command Photograph. (Credit: US Navy)

USS San Diego on Jan. 28, 1915, while serving as flagship of the Pacific Fleet. Her name had been changed from California on Sept. 1, 1914. Note two-star Rear Admiral's flag flying from her mainmast top. U.S. Naval History and Heritage Command Photograph. (Credit: US Navy)

During the presentation, the researchers demonstrated that 3-D images collected by an autonomous underwater vehicle helped support their theory.

“The format of the 3-D modeling data makes analysis readily comparable,” said Ken Nahshon, Ph.D., of the Naval Surface Warfare Center Carderock Division in the statement. “Before we started this, I wasn’t familiar with the ability to do this underwater; above the water we do it all the time, but below water collecting 3-D data is a challenge. I’ve learned that the sheer amount of expertise that’s needed to interpret it is a credit to the advances of technology in sea floor mapping.”

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Since it sank, the USS San Diego has become an artificial reef, home to a variety of marine life, including fish, barnacles and lobster, Live Science added.

Castambis added that the research will help the U.S. Navy in the future, establishing "a baseline informing site formation processes and management of USS San Diego,” adding that the lessons learned here can be applied to other sunken military craft.

Historians have theorized for years what happened to the USS San Diego. German submarines mined the coast but researchers were not able to definitively point to mines as the root cause of the explosion.

Some theories suggested that it may have been caused by a torpedo (despite the fact no submarine or torpedo trail was spotted) or a coal bunker explosion or even sabotage.

Follow Chris Ciaccia on Twitter @Chris_Ciaccia