After the SS trial Sommer received a reduction in rank and was sentenced to a penal battalion fighting on the Eastern Front where he was wounded in a tank explosion, losing his left arm and right leg. He was taken captive by the Red Army and was detained as P.O.W. until 1950 when his prisoner status was upgraded to war criminal. He was released from Soviet captivity in 1955 as part of the negotiations conducted on behalf of Soviet held German prisoners by Konrad Adenauer.