Invasion of Poland, attack on Poland by Nazi Germany that marked the start of World War II. The invasion lasted from September 1 to October 5, 1939.
As dawn broke on September 1, 1939, German forces launched a surprise attack on Poland. The attack was sounded with the predawn shelling, by the German battleship Schleswig-Holstein, of Polish fortifications at the Baltic port of Danzig (modern Dansk). Sixty-two divisions, with more than 1,300 airplanes in support, then commenced a coordinated assault across the German–Polish border. Army Group North attacked from Pomerania and East Prussia, while Army Group South drove deep into southern Poland from Silesia and Slovakia. Strategically outflanked and materially outnumbered, Polish forces stood little chance, especially because they were deployed too close to the German frontier, unintentionally facilitating Germany’s strategy of envelopment.
The powerful Luftwaffe destroyed the Polish air force in days, leaving the Polish army at the mercy of the German panzer divisions. The speed with which the German tank units cut through the Polish lines was to give a new name to the lexicon of warfare: blitzkrieg (“lightning war”). The declaration of war on Nazi Germany by Britain and France on September 3 did nothing to help Poland.
The Poles enjoyed a limited tactical success from September 9 to 15 at the Bzura River, yet it came to nothing as the German armies closed in on Warsaw. Poland’s fate had already been sealed, when—in accordance with the secret terms of the Nazi-Soviet pact—the Red Army crossed the Polish border from the east on September 17. Warsaw and a few garrisons continued to hold out briefly but eventually surrendered. Poland was divided between Nazi Germany and the Soviet Union.
Before the invasion began, Adolf Hitler’s general staff worried that the assault was premature because the army (Wehrmacht) was not yet at full strength and that victory could not be assured, The invasion was thus a highly calculated risk, one that Hitler was so willing to take that it was originally scheduled to begin a week earlier. The attack on Poland was an initial victory for Germany that surpassed the staff’s initial expectations, but it also galvanized Polish military resistance with the formation of a strong partisan underground that would never flag during the course of World War II and a Polish army in exile that would fight alongside the Allies at major engagements that included Operation Market Garden and the Battle of Monte Cassino.
In the end, German losses totaled 14,000 dead or missing and 30,000 wounded out of a total of 1,250,000 troops involved in the invasion; Polish casualties numbered 66,000 dead, 130,000 wounded, and 400,000 captured out of 800,000 troops.