On 3 March 1958, Topp joined West Germany's navy, at the time named the "Bundesmarine" (Federal Navy), holding the rank of "Fregattenkapitän". His first assignment was with the "Führungsstab der Marine" (Navy Staff). On 16 August 1958, he served with the NATO Military Committee in Washington, D.C., initially as a naval speaker, later as the chief-of-staff of the German delegation in Washington. During this assignment, he was promoted to "Kapitän zur See" (captain at sea/captain) on 1 November 1959. On 1 January 1962, Topp was transferred to the position of commander of the "Bundesmarine"s "Amphibische Streitkräfte" ("amphibious forces"), a position he held until 30 September 1963. In parallel, on 1 November 1962, he was made acting commander of U-boats, serving in this capacity until 1 December 1962.