German submarine U-550

German Type IXC/40 submarines were slightly larger than the original Type IXCs. U-550 had a displacement of 1,144 tonnes (1,126 long tons) when at the surface and 1,257 tonnes (1,237 long tons) while submerged.^[3] The U-boat had a total length of 76.76 m (251 ft 10 in), a pressure hull length of 58.75 m (192 ft 9 in), a beam of 6.86 m (22 ft 6 in), a height of 9.60 m (31 ft 6 in), and a draught of 4.67 m (15 ft 4 in). The submarine was powered by two MAN M 9 V 40/46 supercharged four-stroke, nine-cylinder diesel engines producing a total of 4,400 metric horsepower (3,240 kW; 4,340 shp) for use while surfaced, two Siemens-Schuckert 2 GU 345/34 double-acting electric motors producing a total of 1,000 shaft horsepower (1,010 PS; 750 kW) for use while submerged. She had two shafts and two 1.92 m (6 ft) propellers. The boat was capable of operating at depths of up to 230 metres (750 ft).^[3]

The submarine had a maximum surface speed of 18.3 knots (33.9 km/h; 21.1 mph) and a maximum submerged speed of 7.3 knots (13.5 km/h; 8.4 mph).^[3] When submerged, the boat could operate for 63 nautical miles (117 km; 72 mi) at 4 knots (7.4 km/h; 4.6 mph); when surfaced, she could travel 13,850 nautical miles (25,650 km; 15,940 mi) at 10 knots (19 km/h; 12 mph). U-550 was fitted with six 53.3 cm (21 in) torpedo tubes (four fitted at the bow and two at the stern), 22 torpedoes, one 10.5 cm (4.13 in) SK C/32 naval gun, 180 rounds, and a 3.7 cm (1.5 in) SK C/30 as well as a 2 cm (0.79 in) C/30 anti-aircraft gun. The boat had a complement of forty-eight.^[3]

After training with the 4th U-boat Flotilla, she was assigned to the 10th U-boat Flotilla on 1 February 1944 in Lorient in occupied France.

She sailed from Kiel on 6 February 1944, heading for the North Atlantic, via the gap between Iceland and the Faroe Islands and conducted weather reporting duties before sailing for Newfoundland and subsequently the northeast coast of the United States. On 22 February the boat was unsuccessfully attacked south of Iceland by a Canso flying boat of No. 162 Squadron RCAF. However, two members of the U-boat's crew were killed.^[4]

On 16 April 1944, south of Nantucket Island, she located convoy CU 21, bound for Great Britain from New York City. The Pan Pennsylvania, one of the largest tankers in the world, was unwisely straggling behind the convoy; U-550 torpedoed her. The ship quickly caught fire and began to sink. As the vessel settled, the submerged U-boat maneuvered underneath her hull in an effort to hide from the inevitable counterattack by the convoy's escorts.

Convoy CU-21 was escorted by Escort Division 22, consisting of Coast Guard-crewed destroyer escorts reinforced by one Navy DE, USS Gandy, which took the place of USS Leopold, which had been lost in action the previous month. The escort division's flagship, USS Joyce and USS Peterson rescued the tanker's surviving crew, while the Joyce detected the U-boat on sonar as the Germans attempted to escape after hiding beneath the sinking tanker. U-550's engineering officer later said, "We waited for your ship to leave; soon we could hear nothing so we thought the escort vessels had gone; but as soon as we started to move – bang!"^[5] The Joyce delivered a depth-charge pattern that bracketed the submerged submarine. The depth charges were so well placed, a German reported, that one actually bounced off the U-boat's deck before it exploded.^[5]

According to eyewitness accounts cited in Randall Peffer's book Where Divers Dare: The Hunt for the Last U-boat, the attack severely damaged U-550 and forced it to the surface. Joyce, Peterson and Gandy circled around the submarine, firing at it. Gandy rammed U-550 abaft the conning tower and Peterson dropped two depth charges which exploded near the U-boat's hull. Two men in the U-boat's tower were killed.

Meanwhile, the U-boat captain Klaus Hänert tried to reach the observation deck with a surrender flag, but he was wounded by the American shells and fell back down into the U-boat's control room. Eventually, someone aboard the submarine fired a white flare from the tower hatch.

The captain of the USS Joyce, Robert Wilcox, took the flare as a sign of distress and surrender and called a cease fire. USS Gandy and USS Peterson ceased firing, too. The U-boat's crew scrambled on deck to abandon their sinking vessel. About 40 of the Germans entered the 44-degree water and tried to swim to USS Peterson, but the men were not picked up. Joyce rescued 13 of U-550's crew, including the captain Klaus Hänert, engineer Hugo Renzmann and doctor Friedrich Torge. One of the saved German seamen later died from wounds received during the firefight. Joyce delivered the prisoners of war as well as the Pan Pennsylvania survivors to the authorities in Ireland.

There is a grisly postscript to the sinking of U-550. According to the Eastern Sea Frontier's War Diary account of the sinking.

At 15:15 on 5 May 1944, the Coastal Picket Patrol CGR-3082 recovered a body from the sea at 39°51′N 71°58′W / 39.850°N 71.967°W / 39.850; -71.967, about 93 nmi (172 km; 107 mi) ESE of Ambrose. The body was clothed in a German-type life jacket. From the markings on his clothing it was possible that the man's name was "Zube". A German escape lung was found near his body as well. An autopsy performed on the body indicated that the individual died only five days before his remains were discovered – U-550 had been sunk on 16 April, the corpse was found 19 days later.

Two other bodies were subsequently found. The first, picked up by another picket boat, CGR-1989, at 17:30 on 11 May, was fully clothed, had an escape lung and life jacket on. He was found in a rubber raft. Identification marks indicated the man was a German sailor named Wilhelm Flade, aged about 17. The body was transferred from CGR-1989 to CGR-1338 on the morning of 12 May 1944 and was brought to Tompkinsville on Staten Island.

On 16 May a third body was sighted and picked up by USS SC-630. It was stated that the uniform and insignia indicated the victim had been a German crewman, although he carried no identification; he had been in the water more than 18 days.

The wreck of U-550 was discovered on 23 July 2012. It lay off the coast of Massachusetts in over 300 feet of water about 70 nautical miles (130 km; 81 mi) south of Nantucket. A team of six divers, led by Joe Mazraani, located the wreck using side-scan sonar after a multi-year search.^[6]

Subsequent to the discovery, the divers received emails, letters and phone calls from veterans and the families of veterans involved in the battle who were looking for closure and hoping to set the record straight. The divers interviewed living veterans of the tanker Pan Pennsylvania and the US destroyer escorts. Eventually, the divers traveled to Germany and met with two of the last living survivors of U-550 as well as the families of the submarine's captain and doctor. What the divers learned was that the survivors of U-550 had become friends following the war with the captain of the Joyce, Robert Wilcox, who saved their lives.

During the search for U-550 the team located a large target which diving confirmed to be the wreck of the stern of Pan Pennsylvania, previously believed to have sunk whole approximately 20 nautical miles (37 kilometres; 23 miles) from the scene of battle in 1944. They recovered a breakfast plate from the wreck and presented it to the ship's chief radio officer Mort Raphelson on the 70th anniversary of the battle. The plate resembled the one Raphelson had been eating from when the U-boat's torpedo hit his ship.

• Helgason, Guðmundur. "The Type IXC/40 boat U-550". U-Boat net. Retrieved 28 July 2012.
• Hofmann, Markus. "U 550". Deutsche U-Boote 1935-1945 - u-boot-archiv.de (in German). Retrieved 1 February 2015.
• "U-550 Crew List". Kriegsmarine and U-Boat history. Marinearchiv. Retrieved 15 July 2014. (Please go to the line "U-Bootnr.:" and enter the figure 550. Then scroll down and click the "suchen" button to get a 2-page crew list. Table headers are in German but the data is in English.)
• "1944: April 16: Sinking of German U-boat, U-550". U.S. Navy: National Museum of the U.S. Navy.

40°09′N 69°44′W / 40.150°N 69.733°W / 40.150; -69.733