Frauenheim had been made watch officer on in 1938, eventually spending over a year in this role, until October 1939. He was appointed to command on 1 October 1937, eventually carrying out five patrols, eventually sinking four merchant ships. He also laid
mines, one of which damaged on 21 November, putting her out of action for nearly three years. The
Bayonet was sunk by one of
U-21’s mines on 21 December. Frauenheim left
U-21 on 6 January 1940, taking over command of the newly built on 11 March 1940. He commissioned the boat and took her on four successful patrols. He sank a total of 12 ships, including three sunk and one damaged from
convoy SC 7. He left
U-101 on 18 November 1940 and became a teacher in the 2nd ULD. He went on to hold a number of staff positions, before taking command of
23rd U-boat Flotilla in the
Mediterranean in September 1941. In 1942 he moved to command
29th U-boat Flotilla. On 1 March 1943 he was promoted to
Korvettenkapitän. In February 1944 Frauenheim joined the staff of the Admiral der
Kleinkampfverbände (Admiral of Small Battle Units), where he remained for the rest of the war. He was again promoted, this time to
Fregattenkapitän on 1 December 1944. ==Post war==