Home Dive Site Reviews 100th Anniversary of the Sinking of the cruiser USS San Diego :...

100th Anniversary of the Sinking of the cruiser USS San Diego : Findings of the Two-Year Interdisciplinary, Multi-Agency Inquiry

USS Olympic C-6 at Independence Seaport Museum, Philadelphia, PA

By Gary Lehman

And now it can be told. An interdisciplinary team of ten US Federal agencies, the military, scientists and academicians collaborated on a two-year study of the wreck of USS San Diego on the occasion of the 100th anniversary of its sinking, to determine definitely what happened that day. The study was undertaken in memory of the six sailors killed in the sinking. New technologies were employed in the study, including finite-element engineering modeling of the flooding and sinking timeline based on loads aboard the ship and interior compartmentalization, high density/definition photogrammetry mapping and side scan sonar analysis of the wreck, and underwater unmanned probes (AUV’s and ROV’s – autonomous underwater vehicle and remote-operated vehicle) equipped with laser beams to measure the structure.

The initial court of inquiry finding by the US Navy brass has been confirmed: USS San Diego was sunk by a mine laid by German submarine U165.

US Navy cruiser CA6 – USS_San_Diego–now on the bottom in 110′ off NY’s Fire Island, sunk by a German naval mine

Many of us here in the northeast have dived on the USS San Diego. Many of us have seen photos and videos of the brooding wreck. There is quite a backstory to this ship and its sinking! Towards the end of WWI in July 1918, USS San Diego was on its way from Portsmouth, New Hampshire to NYC (where the sailors were looking forward to a night on the town) – but instead it was sunk by a German naval mine. July 19th, 2018 marked the 100th anniversary of the sinking of this 15,000-ton cruiser, technically called CA-6 (named USS San Diego). San Diego was destroyed by a ‘bottom’ mine, laid by German Uboat U165, and she sank 10 miles southeast of Fire Island, NY. Six sailors were killed in the flooding and blast. USS San Diego was the only major US warship sunk during World War I.  She is on her side in 110’ of water, and is slowly, inexorably, collapsing — and at some point in the not-too-distant future will be completely reclaimed by the ocean with a plume of rust dust …

During WWI, Germany and Britain laid extensive naval mine fields in an attempt to sink each other’s ships, and thus have supremacy on the high seas. Laying of mines can be defensive – to deny the enemy use of certain parts of sea lanes, or to protect friendly shipping by quarantining areas (securing those areas from enemy surface or submarine penetration). Mines can also be used offensively, and can be placed in known or anticipated enemy shipping lanes (with the intention to sink enemy ships).

For purposes of this discussion, mines can either have positive buoyancy and be attached to an anchor on the bottom (in water deeper than 200’), or can be placed on the bottom (in water less than 200’ deep).  In the former case, when a ship strikes a moored mine (generally suspended by a chain from a bottom anchor point extending upwards to just below the water’s surface), the resulting explosion is likely to blow a hole into the ship’s hull when contact is made causing flooding. In the latter case, the displacement of water caused by the explosion of the on-the-bottom-placed mine can split open or even collapse the hull of the ship as it passes over the mine which detonates and causes the displacement of water. This results in the loss of water to support the weight of the ship, which can split the hull or break the back of the hapless vessel.

Owing to naval warfare in the Franco-Prussian war of 1870, Germany got a big head start over the British in naval mine warfare, technology and doctrine. Consequently, German naval mine technology was more advanced than that of the British at the start of WWI. During WWI the German Navy also met with considerably greater success sinking ships than the British did, due to more aggressive, and primarily offensive naval mine tactics. During the war the British captured a German mine and reverse-engineered it; the improved design proved effective for the British – but by then, land-based warfare had become the deciding strategic factor in the war.

USS San Diego was only one of hundreds of Allied ships which were sunk by German naval mines in WWI. Several notable losses of British Navy ships come to mind. Germany got off to a good start in WWI with its naval mine warfare right off the bat. Just a few months after the start of hostilities in 1914, the largest warship to be sunk in WWI – the battleship HMS Audacious – was sunk in October 1914 by a German mine which had just been laid just a few days prior in a likely staging area for British warships. (The humiliation and propaganda value of this loss to the Germans was so great that the sinking was kept secret by the British Admiralty and the press corps until the end of the war. But the Germans knew HMS Audacious had been sunk and reported this). HMS Audacious was just two-years old, having been launched in 1912 and commissioned in 1913, and she was the pride of the British Navy – and then — with her paint barely dry—she was sunk and on the bottom.  Another grievous loss to the British in WWI to a German naval mine was the cruiser HMS Hampshire on June 5,1916 – a stone’s throw from Scotland’s Orkney Island. (HMS Hampshire was almost exactly the same size as USS San Diego). She was on her way to ally Russia with British Secretary of State Lord Kitchener of Khartoum and his entourage to meet with the Russian Imperial War staff to coordinate their fighting strategies in a two-front war against Germany. But shortly after leaving the British anchorage at Scapa Flow, HMS Hampshire hit a German mine. Kitchener was a British field marshal, imperial administrator, revered ‘Conqueror of the Sudan’ (hence Kitchener of Khartoum), commander-in-chief during the South African (Boer) War, and Secretary of State for War at the beginning of World War I. Lord Kitchener, his entire staff, and virtually all of ship’s company were lost in the sinking. There is a massive monument at Orkney’s Marwick headlands, overlooking the spot where HMS Hampshire was destroyed. (I spoke with shopkeepers in Orkney who, to this day, remember their parents and grandparents who were farmers on the fertile Marwick moors, talking about that terrible night of the explosion.)

Another stunning British ship loss to a German naval mine was His Majesty’s Hospital Ship HMHS Brittanic. She was the sister ship to RMS Titanic, and she was newer — with increased safety measures engineered into her resulting from the investigation into Titanic’s loss. Brittanic was discovered by Jacques-Yves Cousteau in 1975, and was the object of several dive expeditions to explore her, and also to determine the circumstances of her sinking. During WWI Germany steadfastly maintained, contrary to British claims at the time, that Brittanic was not torpedoed by a German submarine (and in fact, this was true – Brittanic was NOT sunk by a torpedo attack). Brittanic was a hospital ship and fully-illuminated, with a big ‘red cross’ on each side of the ship, making it impossible to misidentify Brittanic as a man-o-war. Of course, it suited British propaganda purposes at the time to claim that the hospital ship Brittanic was wantonly and viciously torpedoed by “the German Hun”. The reason that the Germans did not reveal that their mine was the cause of the loss of Brittanic is that the British thought that it was impossible to place a mine in over 200’ of water. Patently, this was a false assumption because that is exactly what the Germans did, resulting in the loss of Brittanic. Germany did not want to reveal that it had perfected the technique to put mines into deeper water beyond 200’.(I greatly recommend reading Richie Koehler’s book Mystery Of The Last Olympian http://www.mysteryofthelastolympian.com/ which details the sinking of Brittanic, the human side of the story, the full envelope of historical background, and of course the spell-binding dive operations around the exploration of Brittanic. Be prepared however to not put the book down; trust me, you will read it cover to cover!).

So, taking all this together – we see that the German Admiralty in WWI had a hugely effective naval mine warfare campaign in effect–so much so, that it reached across the Atlantic Ocean in 1918 to sink the USS San Diego, the 100th anniversary of whose sinking we observed in July, 2018!

PS: For those who wish to personally inspect a warship (intact and topside!) which pioneered some of the naval architecture of USS San Diego, visit Independence Seaport Museum in Philadelphia, where museum ship USS Olympia (C6) is restored to its 1898 combat configuration. There are striking visual similarities to USS San Diego (you will readily see the family resemblance, although Olympia is 2/3 the size). Olympia is the oldest steel-hulled ship of the US Navy still afloat. She was forged in battle in the Spanish-American War, and (with other ships of the US fleet,) destroyed the Spanish navy fleet in Manila Harbor in 1898. From her bridge Commodore Dewey famously instructed Olympia‘s captain, “You may fire when you are ready, Gridley” (and …you can actually stand in his footprints on the bridge!).