It then took part in Fall Gelb as a part of Army Group A, participating in the assault through the Ardennes. In March 1941, the corps was upgraded to a motorised corps status and redesignated III Armeekorps (mot). The Corps was attached to Army Group South for Operation Barbarossa, the invasion of the Soviet Union. The corps advanced through Ukraine and took part in the Battle of Brody, Battle of Kiev, Battle of Rostov, Battle of Kharkov and Battle of Uman.