At the outbreak of World War II in September 1939, Germany's armored forces - the Panzerwaffe - were still in their infancy. The restrictions imposed by the Treaty of Versailles meant that German tank development had to be conducted in secret. Initial armor campaigns in Poland were not completely successful and changes were needed before the invasion of France. This book examines the organizational changes, developments in doctrine and tactics, and improved command and control that provided the basis for the spectacular success of the Panzer divisions in 1940. Although the Panzerwaffe was still largely inferior to its enemies in terms of both tank numbers and quality, it effectively adapted and developed those doctrines and principles of warfare that had shaped German fighting since the 19th century. Achieving tactical and operational surprise, the Panzer divisions succeeded in breaking through enemy defences in the Ardennes and enveloping a large number of hostile forces at Dunkirk. The legend of the Blitzkrieg was born.