Since the 1939's invasion of Poland an Oberstleutnant (lieutenant colonel) Weber was the commander of the 481th Infantry Regiment ("Infanterie-Regiment 481"), part of the 256th Infantry Division, which he led in the invasion of Western Europe, fighting in the Netherlands. On May 17, 1940, his regiment succeeded in penetrating the fortress area of Rotterdam. Weber also excelled in the battles for Nieuwpoort and Dunkirk and was awarded the Knight's Cross of the Iron Cross on June 8, 1940. On October 1, 1940, he was promoted to Oberst (colonel).