Nuke the Prinz Eugen!

In July 1946, the United States of America detonated two nuclear weapons on the German heavy cruiser Prinz Eugen as part of Operation Crossroads. You can read the history of Operation Crossroads here, but the BLUF is that the Prinz Eugen was awarded to the United States at the end of World War II as war reparations. The Prinz Eugen was the last of the Kreigsmarine’s ultra-modern heavy cruisers and represented the pinnacle of German naval engineering. The truth of the matter was that the United States didn’t really want the Prinz Eugen, but the ship was a liability and security risk that needed to be disposed of quickly. The solution, nuke it.

The ex-German heavy cruiser Prinz Eugen sitting at anchor in Bikini Atoll.

The ex-German heavy cruiser Prinz Eugen sitting at anchor in Bikini Atoll. National Archives Photo 6234453

In the naval history of World War II, few ships are as storied as the Prinz Eugen. Commissioned as a Hipper-class heavy cruiser soon after the start of the war, the Prinz Eugen’s first combat operation was to accompany the ill-fated battleship Bismarck into the North Sea in 1941. The Battle of the Denmark Straight is well documented and Prinz Eugen acquitted itself well. The heavy cruiser spent most of the war sitting on the coast of France as a deterrence to Allied invasion before accompanying the battlecruisers Scharnhorst and Gneisenau in what became known as the Channel Dash. By May of 1945, Prinz Eugen was the last major ship of the Kreigsmarine still afloat and carried out combat operations against Soviet forces until the final days. Upon the surrender of Nazi Germany, her crew sailed the ship to Denmark for internment in a neutral country.

What to do with the surviving warships of Nazi Germany, Italy and Japan became a major post war issue for the victorious allied powers. The issue was settled at the Potsdam Conference where the Allied nations agreed to establish the Tripartite Naval Commission to oversee a fair sharing of captured vessels. The foreign ships were worthless to the United States and Great Britain who had large and capable fleets. To the surging Soviet Union though, the opportunity presented by these ownerless warships was the chance to become a first rate naval power overnight. The Soviet Union had already captured the unfinished German aircraft carrier Graf Zeppelin and large numbers of highly advanced U-boats. Soviet engineers crawled all over these ships and the more they learned, the more they wanted. It didn’t take long before Comrade Stalin made demands for major warships that were in the possession of the United States and Great Britain.

The unfinished German Aircraft Carrier Gra Zeppelin under Soviet control in September of 1945.

The unfinished German aircraft carrier Graf Zeppelin under Soviet control in September of 1945. At the stern and bow of the ship, the flight deck has been blown upward and off the hull from demolition charges placed by her crew. Soviet forces quickly salvaged the ship but they were prohibited from keeping the vessel by the Potsdam Conference as the damage was considered too extensive. The Graf Zeppelin would have been a major asset for the Soviet Navy if they had been able to incorporate it. The aircraft carrier was 95% complete when Adolf Hitler ordered construction stopped. If it had been equipped with a proper air wing and support vessels, the carrier would have rivaled the American Essex-class carriers in capability. Instead, the Soviet navy filled the ship full of explosives, towed it out to sea and expended it as a target. It would be another two decades before the Soviet Union built an aircraft carrier. Navy History and Heritage Command Photo 78310    

The United States and Great Britain had spent most of World War II doing their best to keep advanced naval technology out of the hands of the Soviet Union. As part of the lend lease program, both countries were required to supply the Soviet Union with naval vessels. The ships that were sent were predominately World War I ear vessels. Notably the United States lent the Soviet Union the Omaha-class light cruiser Milwaukee and Great Britain sent the Revenge-class battleship Royal Sovereign. These vessels were commissioned into the Soviet Navy as the Murmansk and Arkhangelsk respectively. Both were old, worn out and thought of limited value. Despite their short comings, the Soviet navy used the vessels to tie down a significant amount of German forces.

The real warning came on August 18, 1945 when the Soviet Union invaded the Kuril Islands off of Japan. The invasion came as a surprise to the United States who inadvertently made the invasion possible. The United States was desperate for the Soviet Union to enter the war against Japan. Stalin agreed but as part of the deal, he demanded 180 vessels from the United States. In what became known as Project Hula, the United States turned over 180 frigates, minesweepers and transport vessels to the Soviet Union and trained 15000 Soviet naval personnel in Alaska to man them. It was thought that the ships, which were again, mostly warn out old vessels, would be of little use to the Soviet Union. Soon the United States was fearing that the Soviets might invade mainland Japan before they could get there.

The Soviet Union had hoped to keep a large number of German vessels but the United States had worked a trump card into the negotiating for the Tripartite Naval Commission. Any ships that couldn’t be repaired in a short period of time, had to scrapped. The Soviet Union had limited dry dock and shipyard facilities to make extensive repairs to vessels and they found themselves being forced to scrap prized vessels that they had hoped to incorporate into their own navy in accordance with the Potsdam Conference. The United States and Great Britain took advantage of this clause and declared most of the vessels in their possession as extensively damaged and scrapped them. The problem though was that everyone knew that Prinz Eugen was undamaged as her arrival in Denmark was well documented by the media.  The United States didn’t want the Prinz Eugen but the ship was equipped with radar and sonar systems that were a full generation ahead of anything the Soviet Union possessed. The United States took possession of the Prinz Eugen and for a short time she carried the moniker “USS Prinz Eugen” as  she was sailed to the U.S. East Coast where she was evaluated before transiting the Panama Canal. While the Prinz Eugen was officially U.S. government property, under the terms of the Potsdam Conference, the U.S. Navy was supposed to make the ship available to Soviet intelligence experts upon request. The easiest way to prevent that was to keep the ship unavailable for them to analyze.

Prinz Eugen transiting the Panama Canal

The USS Prinz Eugen transiting the Panama Canal in 1946 on her way to the Pacific Coast. Her forward most 8-inch turret has been stripped of its guns which were kept for evaluation on the East coast. The last of her German crew was removed at this point and she proceeded to Bikini Atoll with an American only crew that had trained with their German counterparts. Prinz Eugen was plagued by engine trouble and spent much of this time being towed to where she needed to go. Naval History and Heritage Command Photo 80-G-365071

After the nuclear attacks on Hiroshima and Nagasaki, one of the great unanswered questions was how a nuclear blast would affect a ship at sea. The U.S. Navy took up that challenge in 1946 and began prepping for Operation Crossroads at Bikini Atoll in the Marshall Islands. An entire fleet of 95 ships was assembled at Bikini Atoll that consisted of surplus U.S. ships as well as captured warships. Prinz Eugen was anchored in the harbor in good company. Nearby was the Japanese battleship Nagato, from whose bridge Admiral Yamamoto had directed the Pearl Harbor attack. Next to the Nagato was the Japanese super cruiser Sakawa that had been completed shortly before the end of the war but had never sortied due to lack of fuel. In addition to this was battle hardened aircraft carrier USS Saratoga and Pearl Harbor survivors USS Nevada and USS Pennsylvania, the battleship USS Arizona’s sister ship.

Soviet actions in early 1946 sealed the fate of the Prinz Eugen and other captured warships. The former German light cruiser Nurnberg and the Italian battleship Guilio Cesar had been awarded to the Soviet Navy as war reparations and they promptly commissioned both into service. Soviet naval engineers were reverse engineering advanced German U-boats and creating the design that would become the Whiskey-class submarines (of note, some Whiskey-class subs are still in service with North Korea to this day, almost 70 years after being built!). Allowing the Soviets access to the Prinz Eugen would give them a ship that was still better than anything they had in service or planned for development. On July 1, 1946, Test Able was conducted and Prinz Eugen was nuked.

The Italian battleship Guilio

The Italian battleship Guilio Cesare was a truly remarkable ship. It had originally been built as a dreadnought type battleship before World War I. The Washington Naval Treaty and the subsequent London Naval Treaty placed a prohibition on building new battleships but did not prohibit modernizing existing battleships. In the 1930’s the Italian navy cut the Guilio Cesare in half and significantly lengthened the hull. In this extra space they put all new machinery and in effect turned Guilio Cesare into a fast-battleship. During World War II her career was a roll call of essentially every battle in the Mediterranean Sea. Interned at Malta after Italy surrendered, the ship was turned over to the Soviet Union as a war reparation. The Soviet Union commissioned the battleship as the Novorossiysk in its own Navy and it served as flagship of the Soviet fleet until it strayed into a minefield in 1955 and sank with a large loss of life. It was the Soviet’s success in incorporating foreign warships like the Italian Guilio Cesare and German light cruiser Nurnberg into their navy that strongly influenced the United States and Great Britain to immediately scrap or sink all the foreign warships in their control so the Soviets couldn’t demand them as tribute. Naval History and Heritage Command Photo 111420 

There were several important lessons learned from Operation Crossroads. Probably the two most important was that a ship with its stern to a nuclear blast will usually receive very little damage. Prinz Eugen made it through two tests at Bikini Atoll and the only damage was a broken main mast. To this day it remains standard Navy operating procedure to turn a ship away from a blast in the event of nuclear attack. The second important lesson learned is that while a ship may get very little damage, it can become so contaminated with radiation that the entire crew could be killed within two days of the blast. This was one of the realizations that led to the development of nuclear, biological and chemical filters for ships ventilation systems.

The Able test conducted

The Able test conducted on July 1, 1946 was an aerial drop. A 23-kiloton plutonium device similar but much more powerful than the device dropped on Nagasaki was used. The Prinz Eugen survived this detonation with minimal damage. National Archives Photo 6217458

It was expected that soon after the blast salvage crews would board and take control of Prinz Eugen for a journey back to the United States. A salvage crew was put on board and promptly removed after efforts to scrub the ship clean failed. Nothing could remove the nuclear contamination that the Prinz Eugen had been exposed to. Prinz Eugen was towed to Kwajalein Atoll and anchored there pending a determination of what to do. (Interestingly, there is a 121 minute film of the Prinz Eugen being towed to Kawajalein that was shot by the U.S. Navy. This remains on film and has not yet been digitized, National Archives Identifier 81224 ).  In the end, lack of maintenance determined Prinz Eugen’s fate. On December 22, 1946, the ship that had dueled with British battleships and had battled Soviet forces to the last days of the war, capsized and sank from a minor water leak. The ship was to irradiated to try to save and the only effort made when it was clear she was sinking was to try to pull the ship ashore, that too failed. Prinz Eugen settled into the sea bed and with that, any chance of the Soviets getting their hands on her vanished.

The Baker test conducted on July

The Baker test conducted on July 26, 1946 was an underwater detonation. The Prinz Eugen is among the ships anchored around the plume and survived this second blast with minimal damage. One theory as to why Prinz Eugen eventually sank is that this blast may have caused micro-fractures in the hull that allowed sea water to slowly creep into the cruiser. Regardless, the ships was so radioactively hot that no one was willing to go on board to find out. National Archives Photo 6234446

In the end, Prinz Eugen served a noble purpose for science and that may be her greatest contribution to the world. The wreck today is still radioactively hot but the levels are low enough that you can safely dive on the wreck. The once feared cruiser is now an artificial reef and is slowly being claimed by marine growth. Two of her propellers still sit above the waterline as the third was salvaged for a memorial back in Germany. If you’re ever in the Marshal Islands, the wreck of the Prinz Eugen is accessible to everyone from snorkelers to advanced divers. A dive on the wreck will give you a better view of the ship then the Soviets ever got. That is unless the U.S. Military is testing a ballistic missile and the entire atoll is closed. Calling ahead is advised.

Leave a Reply

Your email address will not be published. Required fields are marked *