World War I marked the industrialization of warfare, and introduced, for the first time on an international arena, weaponry like warplanes, mechanized artillery, tanks, machine guns – and submarines.
But despite having broken out over a century ago, and despite its use of modern technology, some aspects of WWI remain unresolved to this day. In the chaos of war, people, military units and even entire ships can go missing without a trace, and their stories can raise more questions than answers, even after years and years of investigations.
The story of the USS San Diego, which was sunk off the coast of New York in 1918, is one of these mysteries. But unlike others, its investigators finally found answers – nearly a century after it was downed.
01. The Big Ten
The USS San Diego was initially named the USS California. The USS California was constructed at the famed Union Iron Works in San Francisco at the turn of the 20th century. The ship entered service on August 1, 1907, as part of the Pennsylvania-class of cruisers, alongside the USS Pennsylvania, West Virginia, Colorado, Maryland and South Dakota.
These, along with four other Tennessee-class cruisers, were known as the “Big Ten” in the United States Navy, due to their huge size and modern outfitting – but due to technological advancements and new designs, they were soon outclassed by a new type of ship; the Tennessee-class battleship.
02. Changing Names
By 1914, a new class of warships had been introduced. In order to free up state names for the new class of ships, the old Pennsylvania-class cruisers changed their names to cities within the states they were originally named for.
Thus, the USS Pennsylvania became the USS Pittsburgh, the USS West Virginia became the Huntington, and the USS California was renamed the USS San Diego. This harmless name change would soon be infamously linked to the ship.
03. Track Record
As one of the United States Navy’s biggest and most advanced vessels at the time, the newly christened USS San Diego had an impressive track record, having served in both the Atlantic and Pacific oceans on various missions, and taking part in countless military activities.
But a mere three years after its name was changed, the armoured cruiser would be called to serve in one of the most brutal wars in history. One of its missions will become fateful for the ship and make it infamous.
04. World War I
On April 6, 1917, the United States joined its allies – Britain, France and Russia – to fight in World War I. A day later, the USS San Diego was placed in full commission after a brief, two month period on which she was put on reserve.
This began her service in the war as the flagship of the commander of the Pacific Fleet’s Patrol Force but was soon transferred to the Atlantic Fleet off of the East Coast of the United States.
05. The San Diego’s Mission
San Diego’s essential mission was to escort convoys of merchant vessels and other non-combatant ships through the first leg of their dangerous passage through hostile waters, keeping an essential, strategic connection between America and Europe open.
This was a hugely important undertaking, which allowed the United States to stay in touch with its allies during the war, as well as to safely transfer people and much-needed weapons and supplies to the European continent that was torn by war
06. Submarine Infested Waters
Operating out of the North American ports of Tompkinsville, New York, and Halifax, Nova Scotia, the USS San Diego escorted ships through hostile, submarine infested waters – often under difficult weather – and could proudly claim that none of her charges were harmed while under her protection.
Of course, you already know this by now but despite her distinguished service during the war, the USS San Diego would soon find herself at the bottom of the sea. At the time, no one knew how it happened and who was responsible for it.
07. A Normal Day
In the early morning hours of July 18, 1918, the USS San Diego left the Portsmouth Naval Shipyard and set a course of New York – where the ship’s captain, Harley H. Christy (b. 1870 in Circleville, Ohio), had orders to meet and escort a convoy bound for France.
The ship and crew were serviced and ready, and Captain Christy was confident they would be able to carry out the mission successfully, as they’ve done many times before. Of course, as you know by now, it was anything but a normal day or a normal mission.
08. A Routine Mission
This was a routine mission. San Diego’s experienced officers and crew had made the journey south to New York countless times and were eager to get underway with their assignment as soon as possible.
The decks were swabbed, guns were cleaned and the steam ship’s coal supply was full. Little did they know that this would be the last time the ship ever sailed out into open waters.
09. An Explosion
A day after they had left port, the crew of the USS San Diego was still making its way south to New York. But then, at precisely 11:05 am, just as the San Diego was passing the Fire Island Lightship, an explosion rocked the port side of the ship.
San Diego had been hit… very, very close to home. Could this be the first wave of an attack on US shores? Everyone on board was left confused, shaken and shocked. This was all very unusual. Who was bombing the ship?
10. Something Below the Water Line
Something well below the water line had exploded near the port engine room – and damaged the ship in such a way that both the engine room and the adjacent fireroom could not be sealed off from the rest of the ship.
The San Diego was taking on water, fast but the crew remained calm. Sticking to their protocols and following procedures. No one yet knew the extent of the damage sustained by the military vessel was not yet clear.
11. Hull Breach
The USS San Diego, being a warship, was equipped to deal with hull breaches. The ship was built with separate, watertight compartments which could be closed off relatively easily, preventing from water flooding its decks outside of the damaged areas.
In addition to that, the San Diego, like all Pennsylvania-class cruisers, had especially heavy shielding protecting her hull. So, we wonder, how could just one explosion cause so much damage?
12. A Warped Bulkhead
Whatever had hit the ship had managed to breach the hull’s shielding and warp the bulkhead separating two different compartments, which meant that the watertight seal between them had been broken.
Two flooded compartments are much more difficult to contain and deal with than one – and the San Diego was in danger of sinking. What could have caused so much damage with a single hit?
13. A Submarine Attack?
The explosion had struck the San Diego well below the ship’s waterline – which meant that the attack had come from an underwater source. But that didn’t necessarily mean a submarine attack.
While a German U-Boat could definitely have been responsible for this kind of damage, it was also possible the ship had struck an underwater mine. But then, there was another option, which none of the crew wanted to think about.
14. Betrayal?
Another, much less savoury option, was that the ship had been sabotaged – and that one of the sailors had detonated a bomb from inside… or that it had been planted there by a saboteur before the ship even left port.
Could one of the USS San Diego’s crew have betrayed them? Many of men on the ship, had worked on it, since its commission. It was a hard pill to swallow and for some while others were simply weren’t even considering it as an option
15. Full Speed Ahead
Upon hearing the explosion, Captain Christy assumed the ship had suffered a torpedo hit. He decided to react with submarine defence manoeuvres, which included manning all stations and to search the waters for anything that might look like a periscope.
It also meant getting out of the area as quickly as possible – and so, the captain ordered the ship to steam at full speed ahead on both engines. It was only then that the extent of the damage began to make itself known.
16. Engines Down
It didn’t take long after Captain Christy ordered his chief engineer to give him full speed on both engines for him to realize that that would not be possible. The blast – whether sustained by a torpedo, a mine or a bomb – had done more than flood just one engine compartment and a fire room.
Because of the extensive flooding, both engines were out of commission – and the ship’s machinery compartments were taking on water as well. It was starting to look grim for the ship and drastic measures had to be taken.
17. From Bad to Worse
Not long after the Captain was informed of the damage to the engines, things began to look catastrophic. Because of the continued flooding – and the crew’s inability to close off the damaged area – the ship began to tilt on its side.
Any seasoned sailor will tell you that when a ship begins to tilt, that’s is for sure sign to abandon ship. Thankfully, these were not frantic locals but seasoned military-trained sailors and everyone on board calmly went about evacuating.
A very bad sign.
18. Flooding the Gun Deck
Leaning precariously at a nine-degree angle, water was now no longer just rising the lower decks but began to rush in through one of the gun ports, flooding the gun deck. It seemed like the USS San Diego wouldn’t be able to deal with this on her own.
This is when Captain Christy decided to radio in for help. The Captain rushed to the radio room to request any near-by ships for support, thinking this all would be solved with one radio call but of course, it wasn’t that easy.
19. Alone at Sea
As he was forming in his head the morbid report he would have to give, he saw that his trained radio operator had gotten flustered. Apparently, the blast had knocked out the machinery powering the radio.
This all meant that USS San Diego had no way to let Command know they had sustained major damage. It seemed like the blast had managed, with one fell swoop, to take down all essential systems on the ship.
20. Sending for Help
Captain Christy realized that if the USS San Diego had any chance of surviving the hit she’s taken, he would have to ask for help. Without a working radio, Christy turned to his gunnery officer and, allowing him to handpick a small crew, gave him a boat and sent him to shore, to return with help as quickly as possible.
The Captain would have to make a hard decision. The San Diego’s crew were now relying on the help of a single boat with a tiny crew – and hoping they, too, wouldn’t be taken down on their way back to port.
21. Sinking
A mere ten minutes after she had been hit, Armored Cruiser No. 6, the USS San Diego, began to sink. Captain Christy ordered the crew to lower the ship’s life rafts and boats but held off the order to abandon ship until the very last minute.
The San Diego was one of the Navy’s best vessels, and he didn’t want to give her up until he was certain the ship would capsize. It seemed, however, that the order was inevitable. This above picture truly shows how fast it all happened.
22. Abandon Ship!
Finally, when Captain Christy was convinced there was no way the ship could be salvaged, he gave the order every ship’s captain dreads giving. “Abandon ship.” Those were hards worst to digest, especially for a seasoned military captain.
The crew cried out the order from deck to deck, and sailors, technicians and officers left their posts for the last time aboard what was one of the Navy’s proudest vessels. They boarded the emergency lifeboats and rafts in an orderly, disciplined manner, as Captain Christy stayed aboard to make sure everyone evacuated safely.
23. Losses
Twenty-eight minutes after she had sustained a hit, the USS San Diego succumbed to the cold waters of the Atlantic Ocean. Out of the ship’s complement of approximately eight hundred and thirty crew members, only six lives were lost.
Two of them were killed in the original explosion, one fell overboard, two lost their lives in accidents during the evacuation, and one drowned as the ship went down. While there had been losses in life, overall the whole crew went relatively unharmed.
24. Saving the Captain
During the commotion, Captain Christy himself also fell into the water and it was one of the own crewmen, Ferdinando Pocaroba, who pulled him from the water. Pacarobo spotted the captain struggling in the water and did what all his years of training told him “not to do”.
He reached out of the flimsy boat, endangering not only himself but also the balance of the small dingy to give his captain a hand and pull him to safety. Now, altogether it seemed that the worst was over but again, that wasn’t to be.
25. Back at Port
While the USS San Diego sunk to the depths, her gunnery officer, with his small boat and crew, had reached shore in the small seaside community of Point O’ Woods, New York. From there, he was able to contact Navy command, and vessels were immediately dispatched to rescue the San Diego’s crew.
But this was far from being the end of San Diego’s story. It had, after all – or at least, so the captain believed – been sunk by an enemy submarine, which was still at large. The U.S was in the middle of a war and had to take extreme measures to ensure the safety of its civilians.
26. The Hunt for the Submarine
Once the crew of the San Diego had been retrieved, it was time for the US Naval Air Service to begin hunting for the submarine responsible for downing the only major warship to be lost by the United States during its involvement in World War I.
The First Yale Unit, based in Bay Shore, Long Island, launched warplanes to scan the seas in the area of the San Diego’s wreck. Just as their hopes for finding anything substantial were dwindling, they spotted something.
27. A Hit – and a Miss
Dropping bombs on what the naval pilots thought was a submerged submarine around 100 ft below sea level, for a moment it seemed as if they had caught the submarine responsible for the sinking of one of the Navy’s proudest vessels.
But soon after, they realized they were mistaken. They had actually bombed the wreck of the San Diego herself, rather than any enemy vessel – and over a century would pass before the true culprit would be found.
28. An Investigation
In August 1918, the Naval Court of Inquiry decided an investigation of the sinking of the USS San Diego was in order. San Diego was the only major warship to be sunk during the war, and understanding the reasons behind its sinking was essential.
This would prove to be, however, much more difficult a task than they had expected. Captain Christy, an experienced and seasoned naval officer, believed his ship had been sunk by a torpedo. Despite his certainty, there were several issues conflicting with that theory.
29. An Unlikely Torpedo
First, no submarine had been found in the waters surrounding the ship immediately after its sinking. On top of that, no lookout on the ship had seen the typical, tell-tale wake underwater torpedoes create behind them as they are launched towards a target.
And so, while Christy’s experience was taken into account, a torpedo was ruled unlikely by the investigative committee. This left only two other options: a hidden mine, which were very common or crew sabotage.
30. Naval Mines
Naval mines have been in use since the early 19th century, and by World War I, their technology had been perfected. Consisting of an explosive charge surrounded by vials of acid, the mines are triggered when a ship’s hull bumps up against them, crushing the vials which then ignite a battery, which sets off the charge.
Mines can be either free-floating – known as “drifting mines” – or anchored to the ocean’s bottom – known as “moored mines”. Moored mines have the advantage of staying in one place, thereby increasing the likelihood of being struck by a passing ship.
31. An Unlikely Mine
Due to the lack of submarine sightings, as well as there having been found six other mines in the area in which the San Diego has been sunk, a mine seemed like the likeliest cause for the ship’s demise.
Still, something didn’t add up about the mine option, either.
Still, something didn’t add up about the mine option, either. When a ship strikes a mine, she’s most likely to hit it with her bow or forward part of the ship, and not directly on the side. So could there have been another reason for San Diego’s sinking?
32. Sabotage!
If the ship hadn’t been struck by a torpedo and hadn’t been hit by a mine – could she have been sabotaged? In 1999, a theory was advanced that the famed German spy and saboteur, Kurt Jahnke (1882-1945), had planted explosives aboard the ship, causing an explosion in a strategically chosen part of the ship.
This theory wasn’t without merit – Jahnke was based in San Francisco, as was the USS San Diego before she left for the East Coast – but the Naval Historical Center contested the theory.
33. A Conclusion
In August 1918, the investigation concluded that the cause of San Diego’s sinking was due to a naval mine. Still, many of the involved parties remained unconvinced, and the case of the San Diego remained an open – albeit dusty – one, for nearly a century.
In July 2018, the United States Navy News Service reiterated the reason behind the San Diego’s sinking was still unknown – but that would change, later that year. Over the years, forensic – as well as underwater – technology had greatly advanced.
34. A New Investigation
The case of the USS San Diego continued to intrigue and bamboozle investigators, who were eager to understand how the only major downed United States warship in World War I had been sunk.
In December 2018, at the annual meeting of the American Geophysical Union, this question would finally be answered but like most answers, it left behind far more questions than it solved.
35. An Answer
At the 2018 annual American Geophysical Union meeting, a young underwater archaeologist by the name of Alexis Catsambis, working with the Navy, stated that “We believe that U-156 sunk San Diego”.
Flooding patterns in the ship “weren’t consistent with an explosion set inside the vessel,” thereby removing any chance of sabotage, while the whole “didn’t look like a torpedo strike.”
So, what was a U-156?
36. U-156
In recent years, records of the German army during WWI were released to the public. In them, there is documentation of a submarine named U-156, which had operated along the south shore of Long Island.
U-156 was a mine-laying vessel, and it is believed, after the extensive underwater archaeological work done by Alexis Catsambis and his colleagues, that it was mines deposited by the submarine were responsible for the sinking of the USS San Diego.
Finally, the mystery had been resolved. But what’s happened to San Diego since?
37. The Wreck
Today, the USS San Diego lies under 110 ft (34 meters) of water, off the coast of Fire Island. These are considered comfortable diving depths, and thus, San Diego has become one of the most popular shipwrecks in the United States for SCUBA diving.
Unfortunately, because the wreck lies upside down, it is not a safe diving location for inexperienced divers, and over the years it has claimed more lives in diving accidents than it had while sinking. Still, the site remains extremely popular and is nicknamed “Lobster Hotel” by local divers thanks to the abundance of lobsters that have made it their home.
38. The USS San Diego
The USS San Diego’s story is a fascinating one. It has stood as an unanswered mystery for nearly a century, baffling countless researchers and military historians, sparking up theories, controversy and interest in all who hear it.
It’s amazing to think that after a hundred years of questions, we are finally able to provide answers to one of the most important wrecks in WWI US Naval history – but more than that, it makes us wonder what other unanswered questions lie beneath the sea, waiting to be uncovered… and answered.