German attack on Poland

The invasion of Poland (1 September – 6 October 1939) was a joint attack on the Republic of Poland by Nazi Germany and the Soviet Union which marked the beginning of World War II. The German invasion began on 1 September 1939, one week after the signing of the Molotov–Ribbentrop Pact between Germany and the Soviet Union, and one day after the Supreme Soviet of the Soviet Union had approved the pact. The Soviets invaded Poland on 17 September. The campaign ended on 6 October with Germany and the Soviet Union dividing and annexing the whole of Poland under the terms of the German–Soviet Frontier Treaty. The invasion is also known in Poland as the September campaign ( pl, kampania wrześniowa) or 1939 defensive war ( pl, wojna obronna 1939 roku, links=no) and known in Germany as the Poland campaign (german: Überfall auf Polen, Polenfeldzug).

German forces invaded Poland from the north, south, and west the morning after the Gleiwitz incident. Slovak military forces advanced alongside the Germans in northern Slovakia. As the Wehrmacht advanced, Polish forces withdrew from their forward bases of operation close to the Germany–Poland border to more established defense lines to the east. After the mid-September Polish defeat in the Battle of the Bzura, the Germans gained an undisputed advantage. Polish forces then withdrew to the southeast where they prepared for a long defence of the Romanian Bridgehead and awaited expected support and relief from France and the United Kingdom. On 3 September, based on their alliance agreements with Poland, the United Kingdom and France declared war on Germany; in the end their aid to Poland was very limited. France invaded a small part of Germany in the Saar Offensive, and the Polish army was effectively defeated even before the British Expeditionary Force could be transported to Europe, with the bulk of the BEF in France by the end of September.

On 17 September, the Soviet Red Army invaded Eastern Poland, the territory beyond the Curzon Line that fell into the Soviet "sphere of influence" according to the secret protocol of the Molotov–Ribbentrop Pact; this rendered the Polish plan of defence obsolete. Facing a second front, the Polish government concluded the defence of the Romanian Bridgehead was no longer feasible and ordered an emergency evacuation of all troops to neutral Romania. On 6 October, following the Polish defeat at the Battle of Kock, German and Soviet forces gained full control over Poland. The success of the invasion marked the end of the Second Polish Republic, though Poland never formally surrendered.

On 8 October, after an initial period of military administration, Germany directly annexed western Poland and the former Free City of Danzig and placed the remaining block of territory under the administration of the newly established General Government. The Soviet Union incorporated its newly acquired areas into its constituent Byelorussian and Ukrainian republics, and immediately started a campaign of Sovietization. In the aftermath of the invasion, a collective of underground resistance organizations formed the Polish Underground State within the territory of the former Polish state. Many of the military exiles who escaped Poland joined the Polish Armed Forces in the West, an armed force loyal to the Polish government-in-exile.

Background

On 30 January 1933, the National Socialist German Workers' Party, under its leader Adolf Hitler, came to power in Germany. While some dissident elements within the Weimar Republic had long sought to annex territories belonging to Poland, it was Hitler's own idea and not a realization of any pre-1933 Weimar plans to invade and partition Poland, annex Bohemia and Austria, and create satellite or puppet states economically subordinate to Germany. As part of this long-term policy, Hitler at first pursued a policy of rapprochement with Poland, trying to improve opinion in Germany, culminating in the German–Polish Non-Aggression Pact of 1934. Earlier, Hitler's foreign policy worked to weaken ties between Poland and France and attempted to manoeuvre Poland into the Anti-Comintern Pact, forming a cooperative front against the Soviet Union. Poland would be granted territory to its northeast in Ukraine and Belarus if it agreed to wage war against the Soviet Union, but the concessions the Poles were expected to make meant that their homeland would become largely dependent on Germany, functioning as little more than a client state. The Poles feared that their independence would eventually be threatened altogether; historically Hitler had already denounced the right of Poland to independence in 1930, writing that Poles and Czechs were a "rabble not worth a penny more than the inhabitants of Sudan or India. How can they demand the rights of independent states?"

The population of the Free City of Danzig was strongly in favour of annexation by Germany, as were many of the ethnic German inhabitants of the Polish territory that separated the German exclave of East Prussia from the rest of the Reich. The Polish Corridor constituted land long disputed by Poland and Germany, and was inhabited by a Polish majority. The Corridor had become a part of Poland after the Treaty of Versailles. Many Germans also wanted the urban port city of Danzig and its environs (comprising the Free City of Danzig) to be reincorporated into Germany. Danzig city had a German majority, and had been separated from Germany after Versailles and made into the nominally independent Free City. Hitler sought to use this as '' casus belli'', a reason for war, reverse the post-1918 territorial losses, and on many occasions had appealed to German nationalism, promising to "liberate" the German minority still in the Corridor, as well as Danzig.

The invasion was referred to by Germany as the 1939 Defensive War (''Verteidigungskrieg'') since Hitler proclaimed that Poland had attacked Germany and that "Germans in Poland are persecuted with a bloody terror and are driven from their homes. The series of border violations, which are unbearable to a great power, prove that the Poles no longer are willing to respect the German frontier."

Poland participated with Germany in the partition of Czechoslovakia that followed the Munich Agreement, although they were not part of the agreement. It coerced Czechoslovakia to surrender the region of Český Těšín by issuing an ultimatum to that effect on 30 September 1938, which was accepted by Czechoslovakia on 1 October. This region had a Polish majority and had been disputed between Czechoslovakia and Poland in the aftermath of World War I. The Polish annexation of Slovak territory (several villages in the regions of Čadca, Orava and Spiš) later served as the justification for the Slovak state to join the German invasion.

By 1937, Germany began to increase its demands for Danzig, while proposing that an extraterritorial roadway, part of the Reichsautobahn system, be built in order to connect East Prussia with Germany proper, running through the Polish Corridor. Poland rejected this proposal, fearing that after accepting these demands, it would become increasingly subject to the will of Germany and eventually lose its independence as the Czechs had. Polish leaders also distrusted Hitler. The British were also wary of Germany's increasing strength and assertiveness threatening its balance of power strategy. On 31 March 1939, Poland formed a military alliance with the United Kingdom and with France, believing that Polish independence and territorial integrity would be defended with their support if it were to be threatened by Germany. On the other hand, British Prime Minister Neville Chamberlain and his Foreign Secretary, Lord Halifax, still hoped to strike a deal with Hitler regarding Danzig (and possibly the Polish Corridor). Chamberlain and his supporters believed war could be avoided and hoped Germany would agree to leave the rest of Poland alone. German hegemony over Central Europe was also at stake. In private, Hitler said in May that Danzig was not the important issue to him, but pursuit of ''Lebensraum'' for Germany.

Breakdown of talks

With tensions mounting, Germany turned to aggressive diplomacy. On 28 April 1939, Hitler unilaterally withdrew from both the German-Polish Non-Aggression Pact of 1934 and the Anglo-German Naval Agreement of 1935. Talks over Danzig and the Corridor broke down and months passed without diplomatic interaction between Germany and Poland. During this interim period, the Germans learned that France and Britain had failed to secure an alliance with the Soviet Union against Germany, and that the Soviet Union was interested in an alliance with Germany against Poland. Hitler had already issued orders to prepare for a possible "solution of the Polish problem by military means" through the Case White scenario.

In May, in a statement to his generals while they were in the midst of planning the invasion of Poland, Hitler made it clear that the invasion would not come without resistance as it had in Czechoslovakia:Clark, Lloyd, ''Kursk: The Greatest Battle: Eastern Front 1943'', 2011, p. 26

On 22 August, just over a week before the onset of war, Hitler delivered a speech to his military commanders at the Obersalzberg:

With the surprise signing of the Molotov–Ribbentrop Pact on 23 August, the result of secret Nazi–Soviet talks held in Moscow, Germany neutralized the possibility of Soviet opposition to a campaign against Poland and war became imminent. In fact, the Soviets agreed not to aid France or the UK in the event of their going to war with Germany over Poland and, in a secret protocol of the pact, the Germans and the Soviets agreed to divide Eastern Europe, including Poland, into two spheres of influence; the western one-third of the country was to go to Germany and the eastern two-thirds to the Soviet Union.

The German assault was originally scheduled to begin at 4:00 a.m. on 26 August. However, on 25 August, the Polish-British Common Defence Pact was signed as an annex to the Franco-Polish alliance (1921). In this accord, Britain committed itself to the defence of Poland, guaranteeing to preserve Polish independence. At the same time, the British and the Poles were hinting to Berlin that they were willing to resume discussions—not at all how Hitler hoped to frame the conflict. Thus, he wavered and postponed his attack until 1 September, managing to in effect halt the entire invasion "in mid-leap".

However, there was one exception: on the night of 25–26 August, a German sabotage group which had not heard anything about a delay of the invasion made an attack on the Jablunkov Pass and Mosty railway station in Silesia. On the morning of 26 August, this group was repelled by Polish troops. The German side described all this as an incident "caused by an insane individual" (see Jabłonków incident).

On 26 August, Hitler tried to dissuade the British and the French from interfering in the upcoming conflict, even pledging that the ''Wehrmacht'' forces would be made available to Britain's empire in the future. The negotiations convinced Hitler that there was little chance the Western Allies would declare war on Germany, and even if they did, because of the lack of "territorial guarantees" to Poland, they would be willing to negotiate a compromise favourable to Germany after its conquest of Poland. Meanwhile, the increased number of overflights by high-altitude reconnaissance aircraft and cross-border troop movements signaled that war was imminent.

On 29 August, prompted by the British, Germany issued one last diplomatic offer, with ''Fall Weiss'' yet to be rescheduled. That evening, the German government responded in a communication that it aimed not only for the restoration of Danzig but also the Polish Corridor (which had not previously been part of Hitler's demands) in addition to the safeguarding of the German minority in Poland. It said that they were willing to commence negotiations, but indicated that a Polish representative with the power to sign an agreement had to arrive in Berlin the next day while in the meantime it would draw up a set of proposals. The British Cabinet was pleased that negotiations had been agreed to but, mindful of how Emil Hácha had been forced to sign his country away under similar circumstances just months earlier, regarded the requirement for an immediate arrival of a Polish representative with full signing powers as an unacceptable ultimatum. On the night of 30/31 August, German Foreign Minister Joachim von Ribbentrop read a 16-point German proposal to ambassador Nevile Henderson. When the ambassador requested a copy of the proposals for transmission to the Polish government, Ribbentrop refused, on the grounds that the requested Polish representative had failed to arrive by midnight. When Polish Ambassador Lipski went to see Ribbentrop later on 31 August to indicate that Poland was favorably disposed to negotiations, he announced that he did not have the full power to sign, and Ribbentrop dismissed him. It was then broadcast that Poland had rejected Germany's offer, and negotiations with Poland came to an end. Hitler issued orders for the invasion to commence soon afterwards.

On 29 August, Polish Minister of Foreign Affairs, Józef Beck ordered military mobilization, but under the pressure from Great Britain and France, the mobilization was cancelled. When the final mobilization started, it added to the confusion.

On 30 August, the Polish Navy sent its destroyer flotilla to Britain, executing the Peking Plan. On the same day, Marshal of Poland Edward Rydz-Śmigły announced the mobilization of Polish troops. However, he was pressured into revoking the order by the French, who apparently still hoped for a diplomatic settlement, failing to realize that the Germans were fully mobilized and concentrated at the Polish border. During the night of 31 August, the Gleiwitz incident, a false flag attack on the radio station, was staged near the border city of Gleiwitz in Upper Silesia by German units posing as Polish troops, as part of the wider Operation Himmler. On 31 August, Hitler ordered hostilities against Poland to start at 4:45 the next morning. However, partly because of the earlier stoppage, Poland finally managed to mobilize only about 70% of its planned forces (only about 900,000 of 1,350,000 soldiers planned to mobilize in first order), and because of that many units were still forming or moving to their designated frontline positions. The late mobilization reduced combat capability of the Polish Army by about 1/3.

Opposing forces

Germany

Germany had a substantial numeric advantage over Poland and had developed a significant military before the conflict. The '' Heer'' (army) had 3,472 tanks in its inventory, of which 2,859 were with the Field Army and 408 with the Replacement Army. 453 tanks were assigned into four light divisions, while another 225 tanks were in detached regiments and companies. Most notably, the Germans had seven ''Panzer'' divisions, with 2,009 tanks between them, using a new operational doctrine. It held that these divisions should act in coordination with other elements of the military, punching holes in the enemy line and isolating selected units, which would be encircled and destroyed. This would be 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 disrupted lines of supply and communications. Together, the new methods were nicknamed "'' Blitzkrieg''" (lightning war). While historian Basil Liddell Hart claimed "Poland was a full demonstration of the ''Blitzkrieg'' theory", some other historians disagree.

Aircraft played a major role in the campaign. Bombers also attacked cities, causing huge losses amongst the civilian population through terror bombing and strafing. The ''Luftwaffe'' forces consisted of 1,180 fighters, 290 Ju 87 ''Stuka'' dive bombers, 1,100 conventional bombers (mainly Heinkel He 111s and Dornier Do 17s), and an assortment of 550 transport and 350 reconnaissance aircraft. In total, Germany had close to 4,000 aircraft, most of them modern. A force of 2,315 aircraft was assigned to ''Weiss''. Due to its earlier participation in the Spanish Civil War, the ''Luftwaffe'' was probably the most experienced, best-trained and best-equipped air force in the world in 1939.

Poland

Emerging in 1918 as an independent country after 123 years after the Partitions of Poland, the Second Polish Republic, when compared with countries such as United Kingdom or Germany, was a relatively indigent and mostly agricultural country. The partitioning powers did not invest in the development of industry, especially in the armaments industry in ethnically Polish areas. Moreover, Poland had to deal with damage caused by World War I. This resulted in the need to build a defense industry from scratch. Between 1936 and 1939, Poland invested heavily in the newly created Central Industrial Region. Preparations for a defensive war with Germany were ongoing for many years, but most plans assumed fighting would not begin before 1942. To raise funds for industrial development, Poland sold much of the modern equipment it produced. In 1936, a National Defence Fund was set up to collect funds necessary for strengthening the Polish Armed forces. The Polish Army had approximately a million soldiers, but not all were mobilized by 1 September. Latecomers sustained significant casualties when public transport became targets of the ''Luftwaffe''. The Polish military had fewer armored forces than the Germans, and these units, dispersed within the infantry, were unable to effectively engage the Germans.

Experiences in the Polish–Soviet War shaped Polish Army organizational and operational doctrine. Unlike the trench warfare of World War I, the Polish–Soviet War was a conflict in which the cavalry's mobility played a decisive role. Poland acknowledged the benefits of mobility but was unable to invest heavily in many of the expensive, unproven inventions since then. In spite of this, Polish cavalry brigades were used as mobile mounted infantry and had some successes against both German infantry and cavalry.

An average Polish infantry division consisted of 16,492 soldiers and was equipped with 326 light and medium machine guns, 132 heavy machine guns, 92 anti-tank rifles and several dozen light, medium, heavy, anti-tank and anti-airplane field artillery. Contrary to the 1,009 cars and trucks and 4,842 horses in the average German infantry division, the average Polish infantry division had 76 cars and trucks and 6,939 horses.

The Polish Air Force (''Lotnictwo Wojskowe'') was at a severe disadvantage against the German ''Luftwaffe'' due to inferiority in numbers and the obsolescence of its fighter planes. However, contrary to German propaganda, it was not destroyed on the ground—in fact it was successfully dispersed before the conflict started and not a single one of its combat planes was destroyed on the ground in the first days of the conflict.Michael Alfred Peszke, ''Poland's Preparation for World War II'', ''Military Affairs'' 43 (Feb 1979): 18–24 In the era of fast progress in aviation the Polish Air Force lacked modern fighters, vastly due to the cancellation of many advanced projects, such as the PZL.38 Wilk and a delay in the introduction of a completely new modern Polish fighter PZL.50 Jastrząb. However, its pilots were among the world's best trained, as proven a year later in the Battle of Britain, in which the Poles played a notable part.Michael Alfred Peszke, ''Polish Underground Army, the Western Allies, and the Failure of Strategic Unity in World War II'', McFarland & Company, 2004,
Google Print, p. 2
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Overall, the Germans enjoyed numerical and qualitative aircraft superiority. Poland had only about 600 aircraft, of which only PZL.37 Łoś heavy bombers were modern and comparable to their German counterparts. The Polish Air Force had roughly 185 PZL P.11 and some 95 PZL P.7 fighters, 175 PZL.23 ''Karaś'' Bs, 35 ''Karaś'' as light bombers. However, for the September Campaign, not all of those aircraft were mobilized. By 1 September, out of about 120 heavy bombers PZL.37s produced, only 36 PZL.37s were deployed, the rest being mostly in training units. All those aircraft were of indigenous Polish design, with the bombers being more modern than fighters, according to the Ludomił Rayski air force expansion plan, which relied on a strong bomber force. The Polish Air Force consisted of a 'Bomber Brigade', 'Pursuit Brigade' and aircraft assigned to the various ground armies. The Polish fighters were older than their German counterparts; the PZL P.11 fighter—produced in the early 1930s—had a top speed of only , far less than German bombers. To compensate, the pilots relied on its maneuverability and high diving speed. The Polish Air Force's decisions to strengthen its resources came too late, mostly due to budget limitations. As a "last minute" order in the summer of 1939, Poland bought 160 French Morane-Saulnier M.S.406 fighters and 111 English airplanes (100 light bombers Fairey Battle, 10 Hurricanes and 1 Supermarine Spitfire; the sale of 150 Spitfires asked by the Polish government was rejected by the Air Ministry). Despite the fact that some of the airplanes had been shipped to Poland (the first transport of purchased aircraft on the ship "Lassel" sailed from Liverpool on 28 August), none of them would take part in combat. In late 1938, the Polish Air Force also ordered 300 advanced PZL.46 Sum light bombers, but due to a delay in starting mass production, none of them were delivered before 1 September. When in the spring of 1939 it turned out that there were problems with the implementation of the new PZL.50 Jastrząb fighter, it was decided to temporarily implement the production of the fighter PZL P 11.G Kobuz. Nevertheless, due to the outbreak of the war, not one of the ordered 90 aircraft of this type were delivered to the army.

The tank force consisted of two armored brigades, four independent tank battalions and some 30 companies of TKS tankettes attached to infantry divisions and cavalry brigades. A standard tank of the Polish Army during the invasion of 1939 was the 7TP light tank. It was the first tank in the world to be equipped with a diesel engine and 360° Gundlach periscope. The 7TP was significantly better armed than its most common opponents, the German ''Panzer'' I and II, but only 140 tanks were produced between 1935 and the outbreak of the war. Poland had also a few relatively modern imported designs, such as 50 Renault R35 tanks and 38 Vickers E tanks.

The Polish Navy was a small fleet of destroyers, submarines and smaller support vessels. Most Polish surface units followed Operation Peking, leaving Polish ports on 20 August and escaping by way of the North Sea to join with the British Royal Navy. Submarine forces participated in Operation Worek, with the goal of engaging and damaging German shipping in the Baltic Sea, but they had much less success. In addition, many merchant marine ships joined the British merchant fleet and took part in wartime convoys.

Details

German plan

The September Campaign was devised by General Franz Halder, the chief of the general staff, and directed by General Walther von Brauchitsch, the commander in chief of the upcoming campaign. It called for the start of hostilities before a declaration of war, and pursued a doctrine of mass encirclement and destruction of enemy forces. The infantry, far from completely mechanized but fitted with fast-moving artillery and logistic support, was to be supported by ''Panzers'' and small numbers of truck-mounted infantry (the ''Schützen'' regiments, forerunners of the '' panzergrenadiers'') to assist the rapid movement of troops and concentrate on localized parts of the enemy front, eventually isolating segments of the enemy, surrounding, and destroying them. The prewar "armoured idea", which an American journalist in 1939 dubbed ''Blitzkrieg'', which was advocated by some generals, including Heinz Guderian, would have had the armour punching holes in the enemy's front and ranging deep into rear areas, but the campaign in Poland would be fought along more traditional lines. That stemmed from conservatism on the part of the German High Command, which mainly restricted the role of armour and mechanized forces to supporting the conventional infantry divisions.

Poland's terrain was well suited for mobile operations when the weather co-operated; the country had flat plains, with long frontiers totalling almost , Poland's long border with Germany on the west and north, facing East Prussia, extended . They had been lengthened by another on the southern side in the aftermath of the 1938 Munich Agreement. The German incorporation of Bohemia and Moravia and creation of the German puppet state of Slovakia meant that Poland's southern flank was also exposed.

Hitler demanded that Poland be conquered in six weeks, but German planners thought that it would require three months. They intended to exploit their long border fully with the great enveloping manoeuver of ''Fall Weiss''. German units were to invade Poland from three directions:
* A main attack over the western Polish border, which was to be carried out by Army Group South, commanded by Colonel General Gerd von Rundstedt, attacking from German Silesia and from the Moravian and Slovak border. General Johannes Blaskowitz's 8th Army was to drive eastward against Łódź. General Wilhelm List's 14th Army was to push on toward Kraków and to turn the Poles' Carpathian flank. General Walter von Reichenau's 10th Army, in the centre with Army Group South's armour, was to deliver the decisive blow with a northeastward thrust into the heart of Poland.
* A second route of attack from northern Prussia. Colonel General Fedor von Bock commanded Army Group North, comprising General Georg von Küchler's 3rd Army, which was to strike southward from East Prussia, and General Günther von Kluge's 4th Army, which was to attack eastward across the base of the Polish Corridor.
* A tertiary attack by part of Army Group South's allied Slovak units from Slovakia.
* From within Poland, the German minority would assist by engaging in diversion and sabotage operations by ''Volksdeutscher Selbstschutz'' units that had been prepared before the war.

All three assaults were to converge on Warsaw, and the main Polish army was to be encircled and destroyed west of the Vistula. ''Fall Weiss'' was initiated on 1 September 1939 and was the first operation of Second World War in Europe.

Polish defence plan

The Polish determination to deploy forces directly at the German-Polish border, prompted by the Polish-British Common Defence Pact, shaped the country's defence plan, "Plan West". Poland's most valuable natural resources, industry and population were along the western border in Eastern Upper Silesia. Polish policy centred on their protection, especially since many politicians feared that if Poland retreated from the regions disputed by Germany, Britain and France would sign a separate peace treaty with Germany like the 1938 Munich Agreement and allow Germany to stay in those regions. The fact that none of Poland's allies had specifically guaranteed Polish borders or territorial integrity was another Polish concern. These reasons made the Polish government disregarded French advice to deploy the bulk of its forces behind natural barriers, such as the Vistula and San Rivers, despite some Polish generals supported the idea to be a better strategy. The West Plan allowed the Polish armies to retreat inside the country, but that was supposed to be a slow retreat behind prepared positions intended to give the armed forces time to complete its mobilization and execute a general counteroffensive with the support of the Western Allies.

In case of a failure to defend most of the territory, the army was to retreat to the south-east of the country, where the rough terrain, the Stryj and Dniestr rivers, valleys, hills and swamps would provide natural lines of defence against the German advance, and the Romanian Bridgehead could be created.

The Polish General Staff had not begun elaborating the "West" defence plan until 4 March 1939. It was assumed that the Polish Army, fighting in the initial phase of the war alone, would have to defend the western regions of the country. The plan of operations took into account the numerical and material superiority of the enemy and, also assumed the defensive character of Polish operations. The Polish intentions were defending the western regions that were judged as indispensable for waging the war, taking advantage of the propitious conditions for counterattacks by reserve units and avoiding it from being smashed before the beginning of Franco-British operations in Western Europe. The operation plan had not been elaborated in detail and concerned only the first stage of operations.

The British and the French estimated that Poland would be able to defend itself for two to three months, and Poland estimated it could do so for at least six months. While Poland drafted its estimates based upon the expectation that the Western Allies would honor their treaty obligations and quickly start an offensive of their own, the French and the British expected the war to develop into trench warfare, much like World War I. The Polish government was not notified of the strategy and based all of its defence plans on promises of quick relief by the Western Allies.

Polish forces were stretched thinly along the Polish-German border and lacked compact defence lines and good defence positions along disadvantageous terrain. That strategy also left supply lines poorly protected. One-third of Poland's forces were massed in or near the Polish Corridor, making them vulnerable to a double envelopment from East Prussia and the west. Another third was concentrated in the north-central part of the country, between the major cities of Łódź and Warsaw. The forward positioning of Polish forces vastly increased the difficulty of carrying out strategic maneuvres, compounded by inadequate mobility, as Polish units often lacked the ability to retreat from their defensive positions, as they were being overrun by more mobile German mechanized formations.

As the prospect of conflict increased, the British government pressed Marshal Edward Śmigły-Rydz to evacuate the most modern elements of the Polish Navy from the Baltic Sea. In the event of war, the Polish military leaders realized that the ships that remained in the Baltic were likely to be quickly sunk by the Germans. Furthermore, since the Danish Straits were well within operating range of the German '' Kriegsmarine'' and ''Luftwaffe'', there was little chance of an evacuation plan succeeding if it were implemented after hostilities began. Four days after the signing of the Polish-British Common Defence Pact, three destroyers of the Polish Navy executed the Peking Plan and so evacuated to Great Britain.

Although the Polish military had prepared for conflict, the civilian population remained largely unprepared. Polish prewar propaganda emphasized that any German invasion would be easily repelled. That made Polish defeats during the German invasion come as a shock to the civilian population. Lacking training for such a disaster, the civilian population panicked and retreated east, spreading chaos, lowering the troops' morale and making road transportation for Polish troops very difficult. The propaganda also had some negative consequences for the Polish troops themselves, whose communications, disrupted by German mobile units operating in the rear and civilians blocking roads, were further thrown into chaos by bizarre reports from Polish radio stations and newspapers, which often reported imaginary victories and other military operations. That led to some Polish troops being encircled or taking a stand against overwhelming odds when they thought they were actually counterattacking or would soon receive reinforcements from other victorious areas.

German invasion

Following several German-staged incidents, such as the Gleiwitz incident, part of Operation Himmler, which German propaganda used as a pretext to claim that German forces were acting in self-defence, one of the first acts of war took place on 1 September 1939. At 04:45, the old German pre-dreadnought battleship ''Schleswig-Holstein'' opened fire on the Polish military transit depot at Westerplatte, in the Free City of Danzig, on the Baltic Sea. However, in many places, German units crossed the Polish border even before that time. Around then, the Luftwaffe attacked a number of military and civilian targets, including Wieluń, the first large-scale city bombing of the war. At 08:00, German troops, still without a formal declaration of war issued, attacked near the Polish village of Mokra. The Battle of the Border had begun. Later that day, the Germans attacked Poland's western, southern and northern borders, and German aircraft began raids on Polish cities. The main axis of attack led eastwards from Germany through the western Polish border. Supporting attacks came from East Prussia, in the north, and a joint German-Slovak tertiary attack by units ( Field Army "Bernolák") from the German-allied Slovak Republic, in the south. All three assaults converged on the Polish capital, Warsaw.

France and Britain declared war on Germany on 3 September, but failed to provide any meaningful support. The German-French border saw only a few minor skirmishes, and most German forces, including 85% of armoured forces, were engaged in Poland. Despite some Polish successes in minor border battles, the 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, causing logistical problems for the Poles. Many Polish Air Force units ran low on supplies, and 98 of their number withdrew into neutral Romania. The Polish initial strength of 400 was reduced to 54 by 14 September and air opposition virtually ceased, with the main Polish air bases destroyed during the first 48 hours of the war.

Germany attacked from three directions on land. Günther von Kluge led 20 divisions that entered the Polish Corridor and met a second force heading to Warsaw from East Prussia. Gerd von Rundstedt's 35 divisions attacked southern Poland. By 3 September, when von Kluge in the north had reached the Vistula River, then some from the German border, and Georg von Küchler was approaching the Narew River, Walther von Reichenau's armour was already beyond the Warta river. Two days later, his left wing was well to the rear of Łódź and his right wing at the town of Kielce. On 7 September, the defenders of Warsaw had fallen back to a line paralleling the Vistula River, where they rallied against German tank thrusts. The defensive line ran between Płońsk and Pułtusk, respectively north-west and north-east of Warsaw. The right wing of the Poles had been hammered back from Ciechanów, about north-west of Pułtusk, and was pivoting on Płońsk. At one stage, the Poles were driven from Pułtusk, and the Germans threatened to turn the Polish flank and thrust on to the Vistula and Warsaw. Pułtusk, however, was regained in the face of withering German fire. Many German tanks were captured after a German attack had pierced the line, but the Polish defenders outflanked them. By 8 September, one of Reichenau's armoured corps, having advanced during the first week of the campaign, reached the outskirts of Warsaw. Light divisions on Reichenau's right were on the Vistula between Warsaw and the town of Sandomierz by 9 September, and List, in the south, was on the San River north and south of the town of Przemyśl. At the same time, Guderian led his 3rd Army tanks across the Narew, attacking the line of the Bug River that had already encircled Warsaw. All of the German armies made progress in fulfilling their parts of the plan. The Polish armies split up into uncoordinated fragments, some of which were retreating while others were launching disjointed attacks on the nearest German columns.

Polish forces abandoned the regions of Pomerelia (the Polish Corridor), Greater Poland and Polish Upper Silesia in the first week. The Polish plan for border defence was a dismal failure. The German advance, as a whole, was not slowed. On 10 September, the Polish commander-in-chief, Marshal Edward Rydz-Śmigły, ordered a general retreat to the south-east, towards the 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 penetrating deeply into eastern Poland. Warsaw, which had undergone heavy aerial bombardment since the first hours of the war, was attacked on 9 September and was put under siege on 13 September. Around then, advanced German forces also reached Lwów, a major city in eastern Poland, and 1,150 German aircraft bombed Warsaw on 24 September.

The Polish defensive plan called for a strategy of encirclement. It would allow the Germans to advance in between two Polish Army groups in the line between Berlin and Warsaw-Lodz, and Armia Prusy would then move in and repulse the German spearhead, trapping it. For that to happen, Armia Prusy needed to be fully mobilized by 3 September. However, Polish military planners failed to foresee the speed of the German advance and assumed that Armia Prusy would need to be fully mobilized by 16 September.


The largest battle during this campaign, the Battle of Bzura, took place near the Bzura

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