World War II/Battle of Poland
On September 1, 1939, the German army launched a massive attack on Poland. On the night before, the German Gestapo staged the Gleiwitz incident. According to Alfred Naujocks, the Gestapo (Germany's secret police) ordered he and a small group of others to dress up as Polish soldiers and seize the Gleiwitz radio station. After seizing the station, Naujocks' group broadcast an anti-German message in Polish. A false flag operation with the intention to provide Germany the Casus belli to invade Poland. However they needed to make the attack more convincing. The Gestapo brought in Franciszek Honiok, a German Silesians who sympathized with Poland that had been captured the previous day. Honiok was dressed up as a saboteur, put to death using lethal injection, and given multiple bullet wounds. This would be used as evidence (given to the press and police) of the supposed Polish attack, as he would be presented as one of the dead attackers.
The German Invasion
Now with a seemingly legitimate reason for the attack, Germany was free to invade Poland. At 08:00, German troops, still without a formal declaration of war issued, attacked near the Polish town of Mokra. The battle of the border had begun. Later that day, the Germans attacked on Poland's western, southern and northern borders, while German aircraft began raids on Polish cities. The main axes of attack led eastwards from Germany proper through the western Polish border. Supporting attacks came from East Prussia in the north, and a co-operative German-Slovak tertiary attack by units (Army "Bernolak") from German-allied Slovakia in the south. All three assaults converged on the Polish capital of Warsaw.
Although Italy had agreed to come to the aid of Germany if it entered war, Mussolini contacted Hitler and told him Italy simply did not have the resources for war at that time.
The Allied governments of France and the British Commonwealth declared war on Germany on September 3; however, they failed to provide any meaningful support. The German-French border saw only a few minor skirmishes, although the majority of German forces, including eighty-five percent of their armoured forces, were engaged in Poland. Despite some Polish successes in minor border battles, German technical, operational and numerical superiority forced the Polish armies to retreat from the borders towards Warsaw and Lwów. The Luftwaffe gained air superiority early in the campaign. By destroying communications, the Luftwaffe increased the pace of the advance which overran Polish airstrips and early warning sites and causing logistical problems for the Poles. Many Polish Air Force units ran low on supplies, 98 of their number withdrew into then-neutral Romania. The Polish initial strength of 400 was reduced to just 54 by September 14 and air opposition virtually ceased.
Polish forces abandoned regions of Pomerania, Greater Poland and Silesia in the first week. The Polish plan for border defence was proven a dismal failure. The German advance as a whole was not slowed. On September 10, the Polish commander-in-chief, Marshal Edward Rydz-Śmigły, ordered a general retreat to the southeast, towards the so-called Romanian bridgehead. Meanwhile, the Germans were tightening their encirclement of the Polish forces west of the Vistula (in the Łódź area and, still farther west, around Poznań) and also penetrating deeply into eastern Poland. Warsaw, under heavy aerial bombardment since the first hours of the war, was attacked on September 9 and was put under siege on September 13. Around that time, advanced German forces also reached the city of Lwów, a major metropolis in eastern Poland.
The largest battle during this campaign, the Battle of Bzura, took place near the Bzura river west of Warsaw and lasted from September 9 to September 19. Polish armies Poznań and Pomorze, retreating from the border area of the Polish Corridor, attacked the flank of the advancing German 8th Army, but the counterattack failed after initial success. After the defeat, Poland lost its ability to take the initiative and counterattack on a large scale.
By September 17, 1939, the Polish defense was already broken, and the only hope was to retreat and reorganise along the Romanian bridgehead. However, these plans were rendered obsolete nearly overnight, when the over 800,000 strong Soviet Union Red Army entered and created the Belarussian and Ukrainian fronts after invading the eastern regions of Poland in violation of the Riga Peace Treaty, the Soviet-Polish Non-Aggression Pact, and other international treaties, both bilateral and multilateral.
Following the Soviet Invasion, all hope for Poland was lost. Polish troops were ordered not to engage the Soviets, but this did not prevent some minor battles. Meanwhile, Polish forces tried to move towards the Romanian bridgehead area, still actively resisting the German invasion. From September 17 to September 20, Polish armies Kraków and Lublin were crippled at the Battle of Tomaszów Lubelski, the second largest battle of the campaign. The city of Lwów capitulated on September 22 because of Soviet intervention; the city had been attacked by the Germans over a week earlier, and in the middle of the siege, the German troops handed operations over to their Soviet allies. Despite a series of intensifying German attacks, Warsaw—defended by quickly reorganised retreating units, civilian volunteers and militia—held out until September 28.
The Modlin Fortress north of Warsaw capitulated on September 29 after an intense 16-day battle. Some isolated Polish garrisons managed to hold their positions long after being surrounded by German forces. Westerplatte enclave's tiny garrison capitulated on September 7, and the Oksywie garrison held until September 19; Hel was defended until October 2.
Despite a Polish victory at the Battle of Szack, after which the Soviets executed all the officers and NCOs they had captured, the Red Army reached the line of rivers Narew, Western Bug, Vistula and San by September 28, in many cases meeting German units advancing from the other direction. Polish defenders on the Hel peninsula on the shore of the Baltic Sea held out until October 2. The last operational unit of the Polish Army, General Franciszek Kleeberg's Samodzielna Grupa Operacyjna "Polesie", surrendered after the four-day Battle of Kock near Lublin on October 6, marking the end of the campaign.
Despite an overall German victory, Germany suffered heavy casualties. Over 16,000 German soldiers were killed, and over 27,000 wounded. Soviet casualties were light, suffering only 737 killed and 1,125 wounded.
On the other side, the Polish casualties were horrendous. 66,000 soldiers were dead, 133,000 more wounded and 694,000 captured. 150,000 Polish civilians were also killed.