Without going through the entire history of HMS Seal, here is its last mission from Uboat.net: April 29, 1940 . HMS Seal started its journey for the operation "DF 7" with 50 Mines from Immingham. The operational aim was to lay a mine barrier near by the Swedish island Vinga. That location was in the German transport route to Norway. May 04, 1940 02.30 a. m. HMS Seal was attacked by a German "He-115" aircraft from the "Küstenfliegergruppe 76" in Aalborg. The boat was slightly damaged. May 04, 1940 09.00 a. m. They started to lay the mine barrier. After 45 minutes all 50 mines have been correctly laid. May 04, 1940 06.30 p. m. HMS Seal was badly damaged by a mine hit and laid on ground at 30 meter depth. May 05, 1940 01.30 a. m. The crew managed to surface the boat and attempted to reach Swedish waters, but one hour later a German Ar-196 seaplane discovered the submarine. The "Arado" under Oblt. Mehrens attacked HMS Seal with 2 bombs and machine-gun fire. A few minutes later a second "Arado" under Oblt. Schmidt also attacked the boat. On board the HMS Seal some of the crew were wounded. Then the boat was captured by the German seaplanes. May 05, 1940 06.30 a. m. German "UJ 128" (Unterseebootsjäger 128; the pre-war trawler Franken) commanded by Kptlt. Otto Lang arrived the place and towed the submarine to the now German naval base Frederikshavn (where the German 12th UJ-flotilla. was located) May 11, 1940 02.30 p. m. HMS Seal was towed by the German tug "Seeteufel" (Sea Devil) and reached Kiel and was brought in to the Germaniawerft yard in Kiel, where the submarine was repaired. It was then used as U-boat UB: On Nov 30, 1940 the former HMS Seal was commissioned as UB commanded by Fregkpt. Bruno Mahn. He was an U-Boat veteran from the World War I (Commander of SM UB-21) and at this time 52 years old. The UB had limited value for the Kriegsmarine except for training and propaganda uses. One benefit for the Germans was that through analysis on the British torpedoes they were influenced to make a better torpedo-detonation device for the German weapons which were at that time highly unreliable. On July 31, 1941 UB was decommissioned from the Kriegsmarine and on May 3, 1945 she was scuttled in Heikendorf Bay (in position 54.22N, 10.11E). Her wreck was later raised and broken up.

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