100 years after the ship sank, the mystery surrounding the tragic end of the USS San Diego (ACR-6) has finally been solved.

On July 19, 1918, at 11:00 a.m., an explosion occurred on the port side of the Pennsylvania-class armored cruiser USS San Diego (ACR-6), formerly known as USS California. The ship sank to the bottom of the Atlantic Ocean in less than half an hour.

Since no one took credit for the attack, historians had to guess who was responsible for almost a century until an underwater archaeologist made a significant discovery a century later.

Service as the USS California

Launched on April 28, 1904, USS California was commissioned three years later. She served in the 2nd Division of the Pacific Fleet, conducting exercises and maneuvers around the West Coast.

California joined the US Navy’s Asiatic Station in March 1912, an East Asiatic-based squadron. During this period, the ship enforced a military presence off the coast of Mexico, protected American interests in Nicaragua, and maintained peace during periods of political unrest. .

In 1914 the armored cruiser was renamed USS San Diego.

Renamed the USS San Diego (ACR-6)

This was only the beginning, as a boiler explosion forced the USS San Diego into limited commission the following year. She resumed her duties as head and commander-in-chief of the Pacific Fleet in February 1917, when she was held in reserve until the entry of the United States into World War I in April of that year.

A day after the US declared war against Germany San Diego was appointed overall Commander, Patrol Force, Pacific Fleet. With the North Atlantic swarming with U-boats, she was ordered to join the Atlantic Fleet on 18 July and escort convoys tasked with navigating the treacherous ocean voyage to Europe.

Exactly one year later, she realized the real risks involved

Shaken by an explosion at-sea

USS San Diego departed Portsmouth Naval Shipyard in Maine on July 18, 1918 for New York. Captain Harley H. The ship, under Christie’s command, navigated a zigzag course while all gun watches, fire companies and lookouts were aloft. warning

Early the next morning there was a huge explosion on the port side of the ship. The crew immediately discovered that the bulkhead near the explosion site had been twisted, making it difficult to close the watertight doors between the engine room and No. 8 fireroom as they fought to keep the San Diego from sinking.

Sinking of the USS San Diego (ACR-6)

As the flood continued, Captain Christie gave the order to proceed at full speed, believing that they had been attacked by German U-boats. USS San Diego was not only unable to move fast, but unable to move at all as her machinery compartments filled with water and both of her engines failed.

Ten minutes after the explosion, the San Diego began to list and was sinking. The cruiser was the only significant American battleship lost in World War I, when Christie ordered the lifeboats abandoned. The cruiser was at the bottom of the Atlantic in 28 minutes.

Six of the more than 1,000 crew members on board died in the horrific incident.

Survivors were left with no answers

After the sinking Captain Christie was convinced that he had been hit by a torpedo, even though there was no evidence that a U-boat was nearby and no one had noticed the spot where the torpedo had hit.

Some have speculated that it may have been a sea mine, although it seems unlikely that the explosion would have occurred in the ship’s stern rather than the bow. An official investigation concluded that about six contact mines were found, which caused the sinking by such an explosion. However, the real reason was more complicated.

One hundred years after the USS San Diego sank, USNI News announced in 2018 that the cause of the explosion remained unclear. The American Geophysical Union (AGU) is lucky was about ready to hold its annual conference, where a bombshell revelation a century in the making would be dropped.

What really happened to the USS San Diego (ACR-6)?

A group of researchers from the Naval History and Heritage Command (NHHC) released their results after a two-year study using digital models, 3D scans and historical documents. As undersea archaeologist Alexis Katsmabis said at the 2018 AGU conference, “We believe the U-156 sank the San Diego.”

The hole torn in the USS San Diego’s hull “didn’t look like a torpedo strike,” according to Catsmabis, who also clarified that flood patterns do not indicate that an explosive was triggered aboard the ship. It was determined that SM U-156 had laid a U-boat mine which damaged the armored cruiser.

According to marine scientist Arthur Trembanis, “Torpedoes of the time carried more explosives than mines—and would have caused more immediate damage.” Although the explosion was not particularly strong, San Diego was filled to the brim with coal, making her top-heavy enough to easily capsize as she took on water.

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