 After training with the 5th U-boat Flotilla at Kiel, "U-337" was transferred to the 6th U-boat Flotilla based at Saint-Nazaire in France for front-line service.After sailing from Kiel on 24 December 1942, the U-boat sailed north and then west into the Atlantic south of Iceland.Her last radio report, on 3 January 1943, gave her position as .