Lehmann-Willenbrock transferred to the U-boat arm of the German Navy in April 1939. Upon serving as an
executive officer on , he was promoted to captain and took command of in December 1939. His first patrol, which lasted 15 days, was along the coast of
Norway during
Operation Hartmut, the U-boat operation in support of
the invasion of Norway. Upon the return of
U-5, Lehmann-Willenbrock was transferred to the newly commissioned , a
Type VIIC U-boat. During three patrols under Willenbrock's command,
U-96 sank 125,580 tons of Allied shipping. In 1941,
U-96 sank three British troop ships: (16 January), (17 January) and
Anselm (15 July), each with considerable loss of life. The seventh patrol was the approximate time that
Lothar-Günther Buchheim boarded
U-96 and documented the boat's operations in his book
Das Boot. Lehmann-Willenbrock left
U-96 in March 1942 to be promoted to
Korvettenkapitän and appointed commander of the
9th U-boat Flotilla, stationed in
Brest. On 2 September 1944 he assumed command of and escaped the
besieged Brest just a few days before the town's surrender. He reached
Bergen, Norway, on 23 October. In Bergen he was appointed commander of the
11th U-boat Flotilla in December, and held the position until the German surrender in Norway on 9 May 1945. During his patrols with
U-96, Lehmann-Willenbrock was awarded with the
Iron Cross 2nd Class, the
Iron Cross 1st Class, the
U-Boat War Badge, the
Knight's Cross of the Iron Cross, and the
Knight's Cross of the Iron Cross with Oak Leaves for his achievements. He sank 24 ships for , damaged two ships for and damaged one ship as a total loss for . A total of 1,272 people lost their lives. ==Awards==