During World War II, German U-boats pushed deep into the Gulf of Mexico, carrying out a brief but damaging campaign against Allied shipping. Of the 23 submarines known to have operated in the region, only one—German submarine U-166—was definitively lost due to American action. Although its operational career was short, the circumstances surrounding its destruction later became the subject of decades of dispute within the U.S. Navy.
Commissioned in March 1942 during the Second World War, U-166 was a Type IXC submarine that initially served with the Kriegsmarine’s 4th U-boat Flotilla in a training capacity before transferring to the 10th Flotilla for active combat duty. After conducting early patrols near the British Isles, the submarine relocated to bases in France and eventually crossed the Atlantic to begin operations in the Gulf of Mexico.
During its deployment, German submarine U-166 sank four ships: the Dominican schooner Carmen, the SS Oneida, the fishing vessel Gertrude FV, and most notably the passenger liner SS Robert E. Lee. The attack on the SS Robert E. Lee near the mouth of the Mississippi River on July 30, 1942, triggered the events that sealed the submarine’s fate. The liner’s escort vessel, PC-566, commanded by Lieutenant Commander Herbert G. Claudius, launched a depth-charge attack immediately afterward. Claudius reported that the submarine had been destroyed.
Despite his report, Navy officials doubted the claim. Rather than being commended, Claudius was reassigned to anti-submarine training duties, and the destruction of U-166 remained officially unresolved for many years. The uncertainty surrounding the encounter fueled a long-running debate over what had actually occurred beneath the waters of the Gulf.
On the same day the SS Robert E. Lee was torpedoed during World War II, a United States Coast Guard Grumman J4F-1 Widgeon patrol aircraft sighted a German U-boat off the coast of Louisiana. The crew launched an attack using depth charges and reported scoring a direct hit on the submarine. Despite the claim, Navy officials remained skeptical. Because no wreckage was located at the time, German submarine U-166 and its 52 crew members were officially classified as missing in action.
For almost 60 years, the final resting place of U-166 was unknown. That changed in 2001 when researchers mapping the seafloor near the wreck of the SS Robert E. Lee discovered the submarine roughly two miles away at a depth of around 6,650 feet. Even though part of the wreck was buried beneath layers of silt, its conning tower and deck gun remained visible, allowing investigators to positively identify it.
Since the crew’s remains were still inside the submarine, the wreck was officially designated as a protected war grave.
A detailed examination in 2014 provided new insight into how the submarine was destroyed. Investigators documented extensive damage near the bow, indicating that a depth charge likely detonated on the deck before triggering the submarine’s own torpedoes in a devastating chain reaction. The findings confirmed that the Coast Guard aircraft’s attack, which had previously been doubted, was responsible for sinking U-166 and killing everyone on board.
As a result of this new information, it was determined that PC-566 had actually been responsible for the U-boat’s loss. Claudius was posthumously awarded the Legion of Merit with Combat “V,” with then-Secretary of the Navy Ray Mabus saying, “Seventy years later, we now know that [Claudius’s] report after the action was absolutely correct. [Claudius’s ship] did sink that U-boat, and it’s never too late to set the record straight.”
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U-166 holds the distinction of being the only U-boat to have ever been lost in the Gulf of Mexico.