In April 1940 he participated in the Norwegian Campaign as a Captain. In May 1940 Walther participated in the airborne attack in the Netherlands and was promoted to the rank of Major. In May 1941 he participated in an airborne attack on the island of Crete. Since September 1941 Walther fought on the eastern front, fighting near Leningrad. In January 1942 he was promoted to a Lieutenant Colonel. In July 1943 Walther fought on the island of Sicily, later in mainland Italy. In September 1944 Walther became battlefield commander, fighting in the Arnhem area. In the end of September 1944 he became Commander in the East Front, fighting in East Prussia. In January 1945 until he became a Soviet Prisoner of war on May 8 the same year, Walther was ranked Generalmajor.