# German submarine U-166 (1941)
**German submarine U-166** was a Type IXC ocean-going U-boat of the German Kriegsmarine in the Second World War, the only German U-boat sunk in the [Gulf of Mexico](https://www.edgepedia.org/gulf-of-mexico) during the war. Commissioned in March 1942 under Oberleutnant zur See Hans-Günther Kuhlmann, she sank four ships totaling 7,593 GRT before being destroyed by depth charges from the U.S. patrol craft PC-566 on 30 July 1942, minutes after her last attack. For nearly six decades the sinking was wrongly credited to a Coast Guard aircraft; the wreck's discovery in 2001 corrected the record and led to posthumous recognition of PC-566's commander in 2014.[1](https://uboat.net/boats/u166.htm) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history)
| Key fact | Detail |
|---|---|
| Type and builder | Type IXC; Deutsche Schiff und Maschinenbau AG, Bremen (werk 705); laid down 6 December 1940, launched 1 November 1941, commissioned 23 March 1942[1](https://uboat.net/boats/u166.htm) |
| Commander | Oblt. Hans-Günther Kuhlmann, from commissioning to loss[1](https://uboat.net/boats/u166.htm) |
| War record | 2 patrols; 4 ships sunk, 7,593 GRT total[1](https://uboat.net/boats/u166.htm) |
| Loss | 30 July 1942, Gulf of Mexico at 28.40N, 88.30W, depth charges from USS PC-566; all 52 hands lost[1](https://uboat.net/boats/u166.htm) |
| Wreck | Found 2001 by C&C Technologies AUV during an oil survey for BP Amoco and Shell, about 45 miles south of the Mississippi River mouth, at roughly 1,450 m depth[1](https://uboat.net/boats/u166.htm) • [3](https://repository.library.noaa.gov/view/noaa/23865/noaa_23865_DS1.pdf) |
| Corrected credit | PC-566 officially credited with the kill on 18 December 2014; commander Herbert G. Claudius received a posthumous Legion of Merit with Combat "V"[3](https://repository.library.noaa.gov/view/noaa/23865/noaa_23865_DS1.pdf) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history) |
| War grave | All hands lost; the wreck is considered a war grave that cannot be disturbed[2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history) |
## The boat
U-166 belonged to the Type IXC class, a long-range development of the Type IX design with storage for an additional 43 tons of fuel, giving a surfaced range of 13,450 nautical miles at 10 knots. The class displaced 1,120 tons surfaced, measured 76.76 m overall, carried 22 torpedoes in four bow and two stern tubes, and had a crew of 48 to 56 men.[4](https://uboat.net/types/ixc.htm) U-166 was one of six IXC boats built by Deutsche Schiff und Maschinenbau in Bremen (U-161 through U-166) and was fitted for mine-laying operations.[4](https://uboat.net/types/ixc.htm)
## War patrol in the Gulf
After training with the 4th Flotilla, U-166 joined the 10th Flotilla for active service on 1 June 1942 and was dispatched to the Gulf of Mexico to attack Allied shipping and lay mines near American ports.[1](https://uboat.net/boats/u166.htm) • [5](https://mbac.gmu.edu/mbac_wp/u-166-wreck/) She was one of 17 German U-boats that entered the Gulf in 1942 with orders to interrupt Allied shipping; in the summer of that year they sank 56 Allied vessels, making the Gulf one of the most dangerous bodies of water in the world at the time.[6](https://www.nps.gov/articles/000/3d-laser-and-sonar-scanning-to-monitor-shipwrecks-in-the-gulf-of-mexico.htm)
On 27 July 1942 Kuhlmann radioed German Naval Command reporting completion of mine-laying activities and that he was proceeding to hunt shipping. It was the boat's final message.[7](https://www.bsee.gov/sites/bsee.gov/files/memos/u166-final.pdf)
**The last attack.** On 30 July 1942 the passenger freighter S.S. [Robert E. Lee](https://www.edgepedia.org/robert-e-lee), carrying hundreds of survivors of earlier U-boat attacks, was bound for New Orleans under escort from the newly commissioned patrol craft PC-566 commanded by Herbert G. Claudius. About 45 miles from the [Mississippi River](https://www.edgepedia.org/mississippi-river)'s Southwest Pass, a torpedo from U-166 struck the freighter's starboard side. The ship sank quickly; 25 of the roughly 407 people aboard were killed, the rest rescued by PC-566 and other vessels.[7](https://www.bsee.gov/sites/bsee.gov/files/memos/u166-final.pdf) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history)
During the sinking, PC-566 gained sonar contact on the submarine and dropped ten depth charges across the U-boat's diving path. An oil slick appeared and sonar contact was lost; Claudius reported that he believed the U-boat had been destroyed or mortally wounded. A Navy review board ruled the attack unlikely to have succeeded, and Claudius was removed from command and sent to anti-submarine warfare school.[7](https://www.bsee.gov/sites/bsee.gov/files/memos/u166-final.pdf) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history)
**The false credit.** On 1 August 1942 a U.S. Coast Guard J4F amphibious aircraft piloted by Henry White with radio operator George Boggs attacked a U-boat on the surface about 100 miles south of [Houma, Louisiana](https://www.edgepedia.org/houma-louisiana), with a single depth charge. The aviators were told a year later that they had destroyed U-166 and were decorated. Official records therefore placed U-166's loss at position 28.37N, 90.45W, far west of the true site. Communications later revealed multiple U-boats were in the area, and the boat the plane attacked was only slightly damaged, possibly U-171.[7](https://www.bsee.gov/sites/bsee.gov/files/memos/u166-final.pdf) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history) • [1](https://uboat.net/boats/u166.htm)
## Discovery and identification
After the war U-166 was the only U-boat unaccounted for in the Gulf. In 1986 the wreck and a nearby shipwreck were found in the Mississippi Canyon area during a deep-tow oil and gas survey for Shell Offshore, but the submarine was misidentified as possibly the freighter Alcoa Puritan, another wartime loss in the same area.[5](https://mbac.gmu.edu/mbac_wp/u-166-wreck/)
In 2001 an AUV survey by C&C Technologies, funded by BP Amoco and Shell, showed the two-piece wreck was too small to be Alcoa Puritan, and a subsequent ROV investigation confirmed the wreck was U-166. Its position, about 45 miles south of the Mississippi River mouth and less than one mile from the Robert E. Lee wreck, proved that PC-566's depth charges had destroyed the submarine immediately after the freighter attack.[5](https://mbac.gmu.edu/mbac_wp/u-166-wreck/) • [1](https://uboat.net/boats/u166.htm)
## The wreck site
The wreck lies at about 1,450 m (roughly 5,000 feet) of water, with the bow and stern sections about 140 m apart and a scattered debris field between them. The U-boat was broken in half by the depth-charge explosion, probably detonated close to the deck; the 2003 investigation supports the conclusion that a depth charge ruptured the pressure hull, causing the boat to flood, with a possible internal explosion as she approached the seafloor. Apart from this damage the wreck is in good condition, with intact guns, railings, and conning tower showing anemone and rusticle (icicle-like growths of rust formed on sunken iron wrecks) growth, and the stern section is buried in sediment mounds pushed up by its impact.[3](https://repository.library.noaa.gov/view/noaa/23865/noaa_23865_DS1.pdf) • [8](https://www.researchgate.net/publication/297760845_ROV_Investigations_of_the_DKM_U-166_Shipwreck_Site_To_Document_the_Archaeological_and_Biological_Aspects_of_the_Wreck_Site)
The site has been visited repeatedly since 2001, producing a robust record of ROV footage and photographs. [Robert Ballard](https://www.edgepedia.org/robert-ballard), the oceanographer known for locating the Titanic, mapped the wreck with remotely operated vehicles in 2014 and noted the bow had been blasted into fragments, consistent with a depth charge.[6](https://www.nps.gov/articles/000/3d-laser-and-sonar-scanning-to-monitor-shipwrecks-in-the-gulf-of-mexico.htm) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history) Because all 52 crew members were lost, the wreck is a war grave and cannot be disturbed.[1](https://uboat.net/boats/u166.htm) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history)
## Recognition of PC-566
On 18 December 2014 the U.S. Navy officially credited PC-566 with sinking U-166. Navy Secretary Ray Mabus presented Claudius, who had died in 1981 after a 33-year Navy career, with a posthumous [Legion of Merit](https://www.edgepedia.org/legion-of-merit) with Combat "V" device recognizing heroism in battle; his son Gordon accepted the medal. Mabus stated that Claudius's after-action report had been correct.[3](https://repository.library.noaa.gov/view/noaa/23865/noaa_23865_DS1.pdf) • [2](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history) A 2023 study in the *Journal of Conflict Archaeology* reconstructed the battle sequence mathematically from the historical and archaeological data, further supporting the PC-566 crew's account.[9](https://www.tandfonline.com/doi/full/10.1080/15740773.2023.2187733)
## References
1. [The Type IXC U-boat U-166, uboat.net](https://uboat.net/boats/u166.htm)
2. [72 Years Later, Snubbed Captain Credited With Downing German U-Boat, National Geographic (2014)](https://www.nationalgeographic.com/science/article/141217-german-u-boat-u-166-gulf-mexico-archaeology-history)
3. [Documenting WWII Shipwrecks in the Gulf, Oceanography Vol. 28 No. 1 (2015)](https://repository.library.noaa.gov/view/noaa/23865/noaa_23865_DS1.pdf)
4. [Type IXC long range boats, uboat.net](https://uboat.net/types/ixc.htm)
5. [U-166 (1942), Microbiome Analysis Center, George Mason University](https://mbac.gmu.edu/mbac_wp/u-166-wreck/)
6. [3D Laser and Sonar Scanning to Monitor Shipwrecks in the Gulf of Mexico, U.S. National Park Service](https://www.nps.gov/articles/000/3d-laser-and-sonar-scanning-to-monitor-shipwrecks-in-the-gulf-of-mexico.htm)
7. [ROV Investigations of the DKM U-166 Shipwreck Site, BSEE](https://www.bsee.gov/sites/bsee.gov/files/memos/u166-final.pdf)
8. [ROV Investigations of the DKM U-166 Shipwreck Site (ResearchGate record)](https://www.researchgate.net/publication/297760845_ROV_Investigations_of_the_DKM_U-166_Shipwreck_Site_To_Document_the_Archaeological_and_Biological_Aspects_of_the_Wreck_Site)
9. [Analysis of a World War II battle in the Gulf of Mexico: the German U-boat U-166 and U.S. Navy Patrol Craft 566, Journal of Conflict Archaeology Vol. 18 (2023)](https://www.tandfonline.com/doi/full/10.1080/15740773.2023.2187733)
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*Topic: Encyclopedia › Society and history › Conflict and security › Wars, campaigns, and incidents › Battles, sieges, and engagements › Naval battles and maritime engagements › Warship losses and wartime shipwrecks*
*Initially written Sep 17, 2026 · Reviewed: Sep 30, 2026; Oct 25, 2026 · Edited: Sep 30, 2026; Oct 25, 2026 · Last review: Oct 25, 2026*
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