Herr commanded an infantry regiment, part of the 13th Motorized Infantry Division, from 8 September 1939 to 14 October 1940, taking part in the Invasion of Poland and France. In October 1940, the division was reformed in Vienna as 13th Panzer Division. Herr was given command of 13th Rifle Brigade, which controlled the division's two infantry regiments, on 14 October 1940. In the invasion of Poland, the division used civilians as human shields in the battle with the retreating Polish Prusy Army and on September 8, 1939 attacked a medical column marked with the Red Cross signs near Odrzywół. A day later, soldiers from the division took part in the revenge killing of 11 civilians and two Polish priests including Dean Stanisław Klimecki in the nearby town of Drzewica in retaliation for their own military losses. Killings have also been reported in nearby settlements of Gielniów, Kamienna Wola, Klwów, Ossa, Przysucha, Potok, Rozwady and Zarzęcin. In May 1941 the regiment returned to Germany to take part in Operation Barbarossa, the invasion of the Soviet Union, as part of 1st Panzergruppe under Paul Ludwig Ewald von Kleist in Army Group South. In December 1941, Herr was given acting command of 13th Panzer Division. On 31 October 1942, on the Terek River deep in the Caucasus, Herr suffered a serious head wound, being struck by shrapnel, and was repatriated to Germany to recuperate. He was later appointed commander of the LXXVI Panzer Corps stationed in France; in August 1943 it was sent to Italy. In Italy, his unit faced the British Eighth Army in Calabria, and the U.S. Fifth Army in Salerno. Herr commanded the corps in the Italian Campaign until 24 November 1944. He also temporarily took command of 14th Army for a brief period from late November to mid-December 1944. On 18 December 1944, he was awarded the Swords to the Knight's Cross. On 15 February 1945 he took command of 10th Army. The Allies final and decisive spring 1945 offensive in Italy opened in early April, Herr was defending the Adriatic sector with orders to hold the lines. On 2 May 1945 the 14th army was overrun by British forces, and Herr was taken prisoner. He was never charged for war crimes committed in Russia and released in April 1948.
