Korth and the crew of U-57 headed out for their first war patrol on 25 October 1939, this patrol lasted 12 days, nothing of significance occurred. They returned to port in
Kiel on 5 November 1939. His second patrol was to be more successful. Leaving Kiel on 12 November, operating off of the coast of
East Anglia, Korth and the crew of U-57 sunk their first allied merchant vessel; the
Lithuanian SS Kaunas on the 17th, and on the 19th they sank an additional British merchant vessel; the
SS Stanbrook, striking her with a single torpedo, causing her to break in two. She sank quickly. On their third war patrol, Korth and his crew sunk the
Estonian merchant steamer
Mina on 13 December with the loss of her entire crew of seventeen. On 8 February 1940 U-57 left port again on a war patrol around the
Shetland Islands. Early on the 14th, Korth sank the
MV Gretafield, a tanker from Convoy HX18. On the evening of the 21st, U-57 torpedoed the
SS Loch Maddy but only damaged her, and the
Loch Maddy was able to return to port. Korth's 9th war patrol began on 14 March 1940 and took U-57 east of the
Pentland Firth where he sunk the damaged Norwegian merchant vessel
SS Svinta on 21 March. The
Svinta had already been attacked by
Luftwaffe aircraft the previous day and had caught fire. Korth sunk her with a single torpedo. In the same area, U-57 sank the British oil tanker
Daghestan on 25 March. On 4 April 1940, U-57 left Kiel under sealed orders to take part in ''
'Operation Hartmut','' part of the German invasion of
Denmark and Norway. His orders were opened on the 6th and the boats in the area were ordered to stage just off the Norwegian coast to screen for potential enemy warships, and to protect the troop ships and landing crafts. After their mission had been completed, Korth was ordered to join the 6th U-boat group, which was to operate east of the
Orkney Islands from 9 April. U-57's patrol ended on 7 May when Korth returned to Kiel. In June 1940, Claus Korth was promoted to
Kapitänleutnant, and on 30 July Korth took command of
U-93, a
Type VIIC U-boat. He took U-93 out on its first patrol on 5 October 1940. On the 14th he torpedoed and sunk the British merchant vessel
Hurunui from Convoy OB227, south-west of the
Faroe Islands. On the 16th, he tracked Convoy OB228 and sunk the British & Norwegian merchant ships
Dokka and
Uskbridge in the early hours of the 17th. During his next patrol Korth failed to score any hits and put in at the naval base at
Lorient on 29 November 1940. U-93's next patrol began on 11 January 1941 and saw Korth and his crew patrolling the
south-west coast of Ireland, although numerous convoys had been spotted in U-93's vicinity by
Luftwaffe reconnaissance aircraft, Korth failed to track any. On the 29th, Korth sighted Convoy SC19 south of
Rockall. He torpedoed and sank three ships, the British
SS King Robert, the British tanker
SS W.B. Walker and the Greek
SS Alkaterini. Korth also sank the British
SS Dione II on 4 February with the loss of thirty-four of her crew. On their return journey U-93 was attacked by a
Whitley bomber and was damaged. U-93 arrived safely into Lorient on 14 February. Korth left for the North Atlantic on 3 May and joined up with
U-94,
U-98 and
U-556 on the 11th to form a patrol group south-east of
Greenland. Two days later they were joined by
U-74,
U-97,
U-109 and U-111. The group moved to the south-west on the 15th and formed a new patrol line. On the 19th, Convoy HX126 and the U-boats closed in. On the night of the 21st, Korth sank the
Dutch tanker
MV Elusa east of
Cape Farewell. On the 24th some of the U-boats were ordered to form a patrol line ahead of the fleeing
Bismarck, in the hope of sinking some of her pursuers after she had passed through their line, however the plan was cancelled after
Bismarck changed course and headed for
St. Nazaire. In late May U-93 and U-94 broke off from the group and moved towards Greenland for resupply from the German
auxiliary ship Belchen. On 3 June Belchen was attacked and sunk by two
Royal Navy cruisers. U-93 picked up forty-nine survivors and instead of re-joining the line, she returned to port in St. Nazaire on 10 June. During his final patrol with U-93, Korth headed for operations in the
Central Atlantic but this was unsuccessful. He made multiple patrols together with other U-boats between 22 July and 16 August when they were called off. He returned to port a final time on 21 August 1941. From 1 October 1941 Korth served as an
aide-de-camp to the
2. Admiral der U-Boote, Konteradmiral Hans-Georg von Friedeburg. In June 1942 he was appointed training officer to the 27th U-Boat Flotilla under the command of
Fregattenkapitän Werner Hartmann and from October 1942 under
Korvettenkapitän Erich Topp and was located at
Gotenhafen. In January 1944, Korth was promoted to
Korvettenkapitän, and from March until war's end, he was attached to the Torpedo Trial Institute in
North Eckernförde, where he worked on further development of torpedoes and was one of the military representatives there. However by April 1945, with the advance of the
Red Army, the work of the institution came to a standstill and munitions and staff were moved north to escape the
Soviet advance. Korth was captured by the Western allies and was held in captivity until November 1945. == Post-War ==