"Korvettenkapitän" Harro Schacht was Topp's commander in training on "U-552"s fourth war patrol. The patrol, which began on 18 August and ended on 26 August in Saint-Nazaire, resulted in the sinking of one ship of . This ship had previously been damaged by (Reinhard Suhren). Following this patrol, Topp was promoted to "Kapitänleutnant" (Captain Lieutenant) on 1 September 1941. The fifth war patrol took "U-552" into the North Atlantic, patrolling southeast of Greenland. Topp left Saint-Nazaire on 4 September and sank three ships of . "U-552" returned to Saint-Nazaire on 5 October.