During the Fall of France, on 19 June 1940, approximately 6,000 Polish soldiers in exile under the command of Stanisław Sosabowski
After training with the 8th U-boat Flotilla at Danzig, U-343 was transferred to the 3rd U-boat Flotilla, based at La Pallice in France, for front-line service on 1 November 1943, and then to the 29th U-boat Flotilla, based at Toulon on the Mediterranean coast, on 1 February 1944.
The unit attacked many other significant targets, including aircraft factories in Kassel, Reims, and Brunswick; airfields in Bordeaux, Paris, and Berlin; naval works at La Pallice, Emden, and Kiel; chemical industries in Ludwigshafen; ball-bearing plants in Schweinfurt; and marshalling yards in Brussels, Osnabrück, and Bielefeld.