Following her eighth patrol, "U-30" was retired from front-line service on 15 September 1940 and was assigned to training flotillas in the Baltic for the rest of the war. After her retirement, many of "U-30"s experienced crew members, including Lemp, were transferred to . In the last months of the war, "U-30" was used as a range boat (gunnery platform) before being scuttled by her crew on 4 May 1945 at Flensburg in Kupfermühlen Bay, in order to avoid surrendering the boat to the Allies as part of Operation Regenbogen. The wreck of the U-boat was later raised and broken up in 1948.