Steven J. Zaloga 
Poland 1939 [PDF ebook] 
The birth of Blitzkrieg

A detailed study of the first major conflict of the Second World War, comparing the German Blitzkrieg offensive to the small but formidable Polish defense.The German invasion of Poland on 1 September 1939 began World War II in Europe, pitting the newly modernized army of Europe’s great industrial power against the much smaller Polish army and introducing the world to a new style of warfare Blitzkrieg. Panzer divisions spearheaded the German assault with Stuka dive-bombers prowling ahead spreading terror and mayhem.This book demonstrates how the Polish army was not as backward as it is often portrayed and fielded a tank force larger than that of the contemporary US Army. Its stubborn defence did give the Germans some surprises and German casualties were relatively heavy for such a short campaign.