In August 1939, the signing of the Nazi-Soviet non-aggression pact opened the way for a renewed partition of Poland, the military implementation of which by Germany and the Soviet Union the next month marked the outbreak of the Second World War. Hornig remained at his pastoral post throughout the fighting, and at the start of 1945 was a contemporary witness from within the city of the Red Army's three month Siege of Breslau and the city's subsequent capitulation. After much of the city had been destroyed, and following much death, on 4 May Hornig was one of four leading city clerics to demand publicly that Hermann Niehoff, the German garrison commander surrender Breslau to the Soviets. Niehoff made no answer and in the afternoon Hornig repeated the demand in an address to the troop commanders.