Germany

Germany had a large numerical advantage over Polish forces, and had developed a significant military. The Heer (Army) had some 2,400 tanks organized into six panzer divisions using the new operational doctrine. They theoretically acted with other units to punch holes in the enemy line and isolate selected enemy units, which the infantry would then encircle and destroy. This would be repeated and followed up by less mobile mechanized infantry and foot soldiers. The Luftwaffe (Air Force) provided both tactical and strategic air power, particularly dive bombers that attacked and disrupted the enemy's supply and communications lines. Together the new operational methods were nicknamed blitzkrieg (lightning war), but historians generally hold that German operations during the campaign were conservative, owing more to traditional methods. The strategy of the Wehrmacht (Armed Forces) was more in line with Vernichtungsgedanken, or a focus on envelopment to create pockets in broad-front annihilation.

Aircraft played a major role in the campaign. Bomber aircraft purposely attacked cities and civilian targets causing huge losses amongst the civilian population in what became known as terror bombings. The Luftwaffe forces consisted of 1,180 fighter aircraft: 290 Ju 87 Stuka dive bombers, 290 conventional bombers (mainly of the He 111 type), and an assortment of 240 naval aircraft. In total, Germany had close to 3,000 aircraft (~2,000 of them can be considered militarily modern) with half of them deployed on the Polish front. The Luftwaffe was also the best trained and equipped air force in 1939.

At sea the odds against the Kriegsmarine (German Navy) were much greater in September 1939 than in August 1914, since the Allies in 1939 had many more large surface warships than Germany. However, during the entire war there was to be no clash between the Allied and the German massed fleets, but only the individual operation of German pocket battleships and commerce raiders. In 1939 Germany did have an advantage over the tiny Polish fleet, as the Western Allies were unwilling and unprepared to challenge the Kriegsmarine in the small Baltic Sea.