On 4 December 1940, Topp took command of "U-552" and commissioned the U-boat into the 7th U-boat Flotilla. Following sea trials and training, Topp, with "Leutnant zur See" Siegfried Koitschka as his second watch officer, took "U-552" on its first war patrol on 13 February 1941. The patrol which was destined for the North Atlantic west of Ireland began in Kiel. That day, they headed for Brunsbüttel where they stayed one day. The following day, "U-552" made a stopover at Cuxhaven before leaving for Heligoland on 15 February. After three days at Heligoland, Topp took the boat into the North Atlantic. "U-552"s first patrol ended in Saint-Nazaire, France on 16 March 1941. On this patrol, Topp sank two ships of .