UJ-121 Jochen was a steam trawler that was built in Germany in 1939, and converted into a submarine chaser at the beginning of the Second World War. A mine sank her in the North Sea in 1940, with the loss of 13 of her crew.
Building and registration In 1938–39 Norderwerft Köser & Meyer in Steinwerder, Hamburg built a pair of trawlers for the fishing fleet of C Andersen. The first was built as yard number 720, and launched on 29 January 1939 as Uwe. Her sister ship was built as yard number 721; launched as Jochen; and completed that May.
Jochens registered length was ; her beam was ; and her depth was . Her tonnages were and . She had a cruiser stern, and a single screw. She was equipped with wireless direction finding, and an echo sounding device.
Deutsche Schiff- und Maschinenbau (DeSchiMAG) built her engines in its Seebeck works at Wesermünde in Bremerhaven. Her main engine was a three-cylinder triple-expansion engine. It was supplemented by an exhaust steam turbine, which drove the same propeller shaft via DeSchiMAG's patent Bauer-Wach system of a Föttinger fluid coupling and double-reduction gearing. The combined power of her reciprocating engine plus exhaust turbine was rated at 132 NHP, and gave her a speed of .
Andersen registered Jochen at Hamburg. Her port letter and number were HH 255, and her wireless telegraph call sign was DKAL.
Submarine chaser The Kriegsmarine requisitioned Jochen shortly before the Second World War. She was converted into a submarine chaser, and on 28 July 1939 she was commissioned with the pennant number UJ-121. She joined the 12. U-Bootsjagdflottille ("12th Submarine Chaser Flotilla"), which was formed in September 1939 at Wilhelmshaven.
On 2 September 1940, UJ-121 Jochen was approaching Ostend in German-occupied Belgium when she struck a mine. She sank, and 13 members of her crew were killed. Her wreck blocked the channel that was used by the 2. Schnellbootflottille ("Second E-boat Flotilla").
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