Editor’s note: The following story is modified from a paper presented in May during the Offshore Technology Conference in Houston. It is reprinted in this revised form with permission from C&C Technologies Inc.

In 1942, the world was at war and Germany controlled most of Europe. Hitler launched Operation Drumbeat under the command of Adm. Karl Dönitz. Using the might of Germany’s Unterseebootes, or U-boats, Operation Drumbeat would take the war to the coasts of the United States, as Hitler’s predecessors had done in World War I. This time the U-boats would not be limited to the East Coast, but would extend right into the country’s backyard, the Gulf of Mexico.

In May 1942, with the sinking of the U.S. battleship Norlindo by the German U-507, a wave of destruction began in the Gulf of Mexico. Within just a year, 24 German U-boats entered the Gulf of Mexico, and 17 of them sent 56 merchant vessels to the bottom and damaged 14 others. Two of the vessels that fell victim to this onslaught were the freighters SS Alcoa Puritan and SS Robert E. Lee.

The Alcoa Puritan was a 6,759-ton cargo freighter 397 feet long and 60 feet at beam. She was headed to Mobile, Ala., from Port of Spain, Trinidad, with a load of bauxite. On May 6, 1942, she crossed paths with the U-507, commanded by Horro Schacht. The U-507 sunk the Alcoa Puritan approximately 50 miles southeast of the mouth of the Mississippi River.

A few months later, on July 20, 1942, the passenger freighter Robert E. Lee left Port of Spain for New Orleans with approximately 270 passengers, 131 crew, six Merchant Marines, and limited cargo. Most of the passengers were American construction workers, their families and victims of other U-boat sinkings in the Caribbean. They made their way though the Caribbean with a convoy, but after reaching the Florida Keys they split from the convoy and continued through the Gulf of Mexico with a U.S. naval escort, Patrol Craft (PC) 566. PC-566 was put into action just five months earlier and outfitted as a sub-chaser. It was the first mission for PC-566, and was the first naval mission of her captain, H.C. Claudius.

The telegraph from the bridge of the Robert E. Lee was found standing upright on the seafloor and more than 200 meters off the freighter’s port side. Image courtesy of C & C Technologies Inc

The Robert E. Lee and PC-566 headed through the Gulf of Mexico toward Tampa to take on provisions. Conditions onboard the Robert E. Lee were said to have been horrendous and the passengers requested to disembark at Tampa. The captain agreed, but when a pilot was unavailable to take them into the harbor, he decided to continue on to New Orleans. The naval escort requested instructions from the commander of The Gulf Sea Frontier and was ordered to continue on to New Orleans with the passenger freighter. Just before midnight on July 29, 1942, the Robert E. Lee and PC-566 left Tampa and headed for New Orleans.

At the same time, a German U-boat, the U-166, was patrolling the shipping lanes off the southeastern coast of Louisiana. On July 27, 1942, the U-166, under the command of Hans-Günther Kühlmann, radioed the German Naval Command to say they had finished their mission of laying mines off the mouth of the Mississippi River. This mission was the sub’s first war mission. Kühlmann had known limited success during this patrol. He had sunk a 2,309-ton vessel and two others that together totaled 100 tons. He was eager to add to his tonnage sunk before heading home.

The Robert E. Lee and her escort steamed across the Gulf and were about 45 miles southeast of the Southwest Pass of the Mississippi River. It was July 30, and the summer day was clear and calm. At 4:30 in the afternoon, PC-566 was sending a radio message to the Port Authority of New Orleans when a torpedo slammed into the starboard side of the Robert E. Lee. The vessel began sinking quickly and the naval escort, which had been running about half a mile ahead of the Robert E. Lee, sprang into action.

PC-566 gained sonar contact on the U-boat and dropped two spreads of depth charges across its path as it tried to dive. After the attack, an oil slick appeared on the surface. The PC-566 crew, after sweeping the area without regaining sonar contact with the sub, determined they had either chased the sub from the area or had sunk it. The operation, joined by the naval SC-519 and the pilot boat Underwriter, turned into a rescue mission as they began pulling survivors from the water. The survivors were taken to shore at Venice, La., but 25 people died on the Robert E. Lee.

Two days later, on Aug. 1, a U.S. Coast Guard Grumman J4F seaplane was patrolling out of Houma, La. The pilot was Henry White and his radio operator was George Boggs. About 30 miles off the Louisiana coast they came through the clouds and spotted a German U-boat on the surface. They radioed their position and circled around to attack the enemy sub. The U-boat began to crash dive and quickly slipped beneath the waves as White and Boggs deployed their only weapon, a single depth charge. The charge detonated near the U-boat and White and Boggs reported a light to medium oil slick on the surface. After returning to base they were instructed that the incident was classified. A year later they were informed that they had sunk the U-166 that day.

Unexpected find

For the next 59 years, the location of the U-166 remained a mystery. The area in which it was thought to have sunk is one of the most heavily surveyed regions on the globe. Remote sensing surveys for oil and gas development have crossed the area numerous times. For decades groups have scoured the seafloor searching for the U-166, but no trace of the U-boat was ever identified.

A combination of events would change this situation.

In January 2001, BP and Shell contracted C&C Technologies to survey a route for the Okeanos pipeline. The 100-mile-long pipeline will carry natural gas from fields deep in the Gulf and connect with the Destin pipeline, which goes onshore in Mississippi. Shell reports that the Okeanos pipeline could carry up to 2 billion cubic feet of gas per day and will be the first gas pipeline in waters deeper than 6,000 feet.

C&C used its new HUGIN (High Precision Untethered Geosurvey and Inspection System) 3000 AUV (Autonomous Underwater Vehicle), a deep-water survey vehicle that carries a full array of survey instruments and is capable of faster and more accurate surveys than conventional deep-tow systems.

The HUGIN 3000 is a third-generation AUV by Kongsberg Simrad and the first commercially operated AUV capable of surveying in water depths reaching 3,000 feet. It is integrated with a diverse payload of survey instruments: a swath bathymetry system, side scan sonar, and a subbottom profiler. Because it is an untethered system that runs on internal power, it can operate even in rough seas and at faster speeds with greater mobility and accuracy than conventional towed arrays. An inertial navigation system, coupled with an acoustic tracking system, makes it possible to accurately steer the AUV. Surveying in 1,500 meters of water, the HUGIN 3000 positioning is accurate to within 3 to 6 meters. Conventional towed systems are typically only accurate to 30 meters or more at the same water depth.

A serendipitous combination of factors set the scene for a unique archaeological discovery. The HUGIN 3000 can travel deeper than most commercial AUVs. It can navigate rough waters and is easy to maneuver, which means it can survey large areas in short time periods. The data it collects is high quality. These technological advantages, combined with the luck of where the Okeanos surveys took place, made it possible to find some of history’s relics. The survey detected a large shipwreck at the edge of the AUV’s survey corridor in 1,500 meters of water. C&C marine archaeologists Robert A. Church and Daniel J. Warren contacted archaeologist Dave Ball at the MMS to verify the identity of the vessel as the Robert E. Lee. In order to satisfy engineering concerns of routing a pipeline near a potential debris field, and out of a sense of duty to preserve sites of historical or archaeological significance, BP and Shell sponsored a second investigation survey around the Robert E. Lee and the suspected location of the Alcoa Puritan. BP’s Rick Davey proposed a region grid survey, which was far beyond the few investigation lines the archaeologists had hoped for. Because the survey could be conducted quickly with the AUV while in the area, the oil companies decided to have C&C conduct a 2-mile by 1.5-mile investigation survey in the area to precisely position any wreckage or outlying debris of both shipwrecks.

C&C conducted the first investigation survey in March 2001. The survey was 17 survey lines at 150-meter line spacing for a total of 31.7 nautical line miles. Using the AUV, the entire investigation survey took less than nine hours, a fraction of the 80 or more hours a conventional deep-towed system would have required.

Side scan sonar at 410 kilohertz reveals the sunken German submarine, U-166, in 2001. Image courtesy of C & C Technologies Inc

As the C&C archaeologists analyzed the data, they realized that the scattered debris identified as possibly being the Alcoa Puritan did not match the characteristics expected of a 6,759-ton freighter. The sonar contacts consisted of two large sections lying approximately 500 feet apart with debris of various sizes scattered between them. The largest section of debris measured approximately 200 by 20 feet. The other major section measured approximately 55 by 20 feet. The combined length of the two sections, 255 feet, was just over half the size of the Alcoa Puritan (397 feet long by 60 feet at beam). Although they did not rule out the Alcoa Puritan, Church and Warren hypothesized that the debris were actually the U-166.

The U-166 was a Type IX-C U-boat, a type that measured 252 feet in length by 22 feet at beam. The sonar image, though not conclusive, was almost exactly what the archaeologists anticipated seeing if they were so lucky as to come across the U-166. Circumstantial evidence seemed to support the U-166 hypothesis. The question remained, however, as to how the U-166 could be located more than 140 miles from where it was reportedly bombed, and within less than a mile of the U-boat’s last victim. The answers began to fall into place when Warren suggested that the two Coast Guard aviators had possibly bombed a different U-boat. Research indicated three German U-boats were in the Gulf of Mexico on Aug. 1, 1942: the U-166, U-509, and U-171. Evidence quickly pointed toward U-171 being the U-boat that White and Boggs had attacked.

The U-171, commanded by Günther Pfeffer, entered the Gulf on July 23, 1942, and was operating between Galveston and New Orleans. Pfeffer’s focus was to be on the Port of Galveston, but he found that the waters off Galveston were too shallow and radioed that he was moving toward the New Orleans area. U-171 sank the R. M. Parker Jr. on Aug. 13, 1942, within three miles of where White and Boggs made their attack on a U-boat. U-171 was operating in the right area during the right time period to be that U-boat.

The archaeologists developed a new hypothesis to pinpoint the location of U-166 and to identify the U-boat that White and Boggs attacked. The evidence indicated that the debris to the east of the Robert E. Lee were the remains of the U-166, which PC-566 sank after the sub attacked the Robert E. Lee. That information, combined with the historical research, further indicates that White and Boggs bombed, but did not sink, the U-171 on Aug. 1, 1942.

After meetings among C&C, Shell, BP, the U.S. Coast Guard and the MMS, Shell arranged for a Remote Operating Vehicle (ROV) to take a research team to the wreck sites. Because of the importance of the historical find, BP and Shell sponsored further AUV investigations of the Robert E. Lee and the suspected U-166 sites.

On May 17, the C&C archaeologists looked deeper and with higher resolution. This investigation ran 33 tracklines in 1,500 meters of water and in three different directions. Each trackline was 450 meters long with 10 meters between each. The survey ran much closer to the seafloor — within 15 meters — so that the bathymetry beams were closely spaced. The result was a smaller horizontal footprint per beam on the seafloor, thereby allowing depths to be resolved better and increasing resolution. This tight grid pattern provided excellent data acquisition for detailed examination, and took the AUV less than two hours to complete. Such a survey would have been difficult to accomplish using a towed system because of prohibitive cost and maneuverability.

The first two investigation surveys of the U-boat site collected side scan data simultaneously, at both 120 kilohertz and 410 kilohertz. On May 26 and 27, we conducted a third survey only in 410 kilohertz in order to increase resolution by increasing the ping rate. The results of this survey were spectacular.

The revealing sonar and bathymetric data collected during the archaeological investigations provided further evidence supporting the U-boat hypothesis. The side scan sonar images in 410 kilohertz revealed the conning tower and other features of a U-boat. The dimensions matched exactly with those of the U-166. The side scan sonar image perfectly matched an outline of a type IX-C German U-boat. The bathymetry data showed that the main section of debris was lying in a 2-meter deep impact crater and that the section suspected to be the bow had approximately 2 meters of relief above the seafloor. The next step was to steer the ROV close to the wreck to visually verify and further document the find.

A closer look

On May 31, a research team from BP, Shell, C&C and the MMS headed out to conduct an ROV investigation of the Robert E. Lee and the U-166. Jack Irion, a marine archaeologist, and Richard Anuskiewicz of the MMS joined the archaeologists from C&C and the team of professionals assembled from Shell and BP. The research team used the Gary Chouest, an anchor-handling vessel on contract to Shell and equipped with an Oceaneering Millennium VI ROV.

Retrieval of the HUGIN 3000 AUV (Autonomous Operating Vehicle), the key tool in finding the real location of the U-166. Courtesy of C & C Technologies Inc

The ROV’s first glimpse of the vessel was the unmistakable conning tower of a German U-boat. Clearly visible were the 105-millimeter deck gun and the 37-millimeter and 20-millimeter antiaircraft guns. Every feature videotaped proved to match that of the U-166.

The investigation of the bow section provided a revealing look at what destroyed the U-boat. A large indentation is visible in the top of the deck, and appears to be the result of a depth charge explosion. Just aft of this damaged area, the bow had torn away from the rest of the vessel. The serrated metal flares outward as if ruptured by an internal explosion. Possibly a depth charge exploded right on the deck and ruptured the pressure hull, which in turn caused an internal explosion. It is speculated that either a torpedo or saltwater rushing into the battery room could have caused such an explosion.

The ROV was then moved a mile west to collect detailed videos of the final resting place of the Robert E. Lee, which had subsided into the seafloor so that the torpedo damage hides below the mudline. The ROV recorded the deck gun on the stern, two lifeboats lying off to the port side of the ship and the brass signal bell on the bow. But the most spectacular find from the Robert E. Lee was the ship’s telegraph, which was used to communicate from the bridge to the engine room. The telegraph was found lying more than 200 feet off the port side. It was alone, standing upright on the seafloor. Made of brass, it was in pristine condition and most of the words on its face were legible. The engine room indicator arrow was in the “STOP” position and the handle was back in the “FINISHED WITH ENGINES” position, a command that was never executed.

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