U-521s first patrol ended on 8 December 1942. She put in at Lorient in occupied France, where she had been assigned to the 2nd U-boat Flotilla, commanded by Korvettenkapitän Viktor Schütze of the 1925 naval term. Schütze was greatly admired by Bargsten, he spoke of a four-hour interview that he (Bargsten) had had with the flotilla commander. Bargsten was given credit for having sunk 29,000 tons of shipping and one corvette.
