On the morning of July 18, 1918, in the closing months of World War I, the USS San Diego left the Portsmouth Naval Shipyard, New Hampshire bound for New York. Suddenly, it was struck by an unusual blast. Within just 28 minutes, the hull had flooded and the ship began its journey to the seabed, sealing its fate as the only major US battleship to sink during World War 1.
Amazingly, out of 1,100 crew, only six souls were lost.
Until now, no one was actually sure what caused the explosion. It was first suspected to be a mine, then later a torpedo, however, there wasn't much in the way of evidence to back this up. Over the years, others have suggested it was a sabotage or even just an accident in the coal bunker.
A 2-year project by the US Naval History and Heritage Command has employed the help of underwater robotics, high-resolution 3-D images, and computer modeling to resolve the century-old mystery. Based on the damage to the wreckage and the modeled flooding scenarios they believe the explosion was, in fact, a caused by a mine laid by a German U-boat.
This further backed up German records found after the war that reveal the German submarine U-156 was sailing around New York at the time, plating explosives on warships. Just days later, U-156 actually went on to carry out of the only attack on US soil during the First World War.
“The format of the 3-D modeling data makes analysis readily comparable,” researcher Dr Alexis Catsambis, of the Naval History and Heritage Command’s Underwater Archeology Branch, announced at the American Geophysical Union’s Fall Meeting this week.
“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," he added. "I’ve learned that the sheer amount of expertise that’s needed to interpret it is a credit to the advances of technology in seafloor mapping.”
Now home to hundreds of fish and lobsters, the shipwreck can be found beneath 34 meters (110 feet) of water just off the coast of Fire Island in New York. Dr Catsambis added that the team hopes their underwater excavations will help raise awareness and preserve the wreck site, as well as inform the public about this moment in US history.
“The legacy of the incident is that six men lost their lives on July 18, 1918," Catsambis said.
“With this pro,ject 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 1,100 is a testament to how well they responded to the attack.”