This day in history, September 1, 1939, Nazi Germany invades Poland around 4:45 am, bringing about the start of World War II. Germany had not signed a declaration of war.
The operation for the invasion is code named Fall Weiss (Plan White). The Germans alloted 52 divisions for the invasion (roughly 1.5 million men), including the 6 armored divisions and all of their motorized units.
Of the divisions left to defend against an Anglo-French front, only about 10 were fit for action according to the Germans. General Brauchitsch, the Commander-in-Chief of the German Army, was in command of the campaign in Poland. Chief of the general staff, General Franz Halder devised the campaign.
Fedor Von Bock lead Army Group North, consisting of the 4th Army (Kuchler) and the 3rd Army (Kluge) and Rundstedt lead Army Group South, consisting of the 8th Army (Balskowitz), 10th Army (Reichenau) and 14th Army (List). Air support came from two Air Fleets, commanded by Kesselring and Lohr, which had around 1,600 aircraft.
Army Group South, advancing from Silesia, had to provide the main German attacks. The 8th Army on the left was to advance on Poznan, the main attack was to be delivered by the 10th Army which was to advance in the center to the Vistula River between Warsaw and Sandomierz, while the 14th Army on the right moved towards Krakow and the Carpathian flank. The 4th Army from East Prussia was to move south toward Warsaw and Bug River to the east. The 3rd Army was to cross the Polish Corridor and join the 4th Army so that they can move south.
The Poles had 23 regular infantry divisions prepared with 7 more assembling, 1 weak armored division and an inadequate supply of artillery. They also had a considerable force of cavalry. The reserve units were called up on August 30th, but were not ready for combat.
In the air, almost all the 500 Polish planes were obsolete and proved unable to slow down the German attack. During the day, the Luftwaffe launched air strikes on Warsaw, Lodz and Krakow. The Polish Commander in Chief, Marshal Rydz-Smigly, deployed the stronger parts of his army to the northwestern half of the country, including large forces in the Poznan area and the Polish Corridor in hopes of limiting German gains.
Due to superior training, equipment and strength of the Germans, they had the advantage in the first battles. Many Polish units were overrun before their reinforcements from the reserve mobilization could arrive. Polish technical inferiority leads to crushing early defeats. Three of the four Polish destroyers managed to make their way for Britain before hostilities began .