Question: What did Poland heavily invest in between 1936 and 1939?
About the article "Invasion of Poland", section "Poland".

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The Wałbrzych Special Economic Zone “INVEST-PARK” is in Poland.
The areas of the Wałbrzych Special Economic Zone “INVEST-PARK” are situated in south – western part of Poland, in the centre of the Europe in very close vicinity of the Czech Republic and Germany, what is its undeniable advantage. 
  Stanisławów - Poznań.
The game did not take place due to the Nazi and Soviet attack on Poland, which marked the outbreak of World War II.  
Between 1936 and 1939, Poland invested heavily in the 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 less than half 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 enemy.
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 a mobile mounted infantry and had some successes against both German infantry and cavalry.
The Polish Air Force ("Lotnictwo Wojskowe") was at a severe disadvantage against the German "Luftwaffe", although it was not destroyed on the ground early on as is commonly believed.
The Polish Air Force lacked modern fighters, but 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 major part.
Overall, the Germans enjoyed numerical and qualitative aircraft superiority.
Poland had only about 600 aircraft, of which only 37 P-37 "Łoś" bombers were modern and comparable to its 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, and by September, over 100 PZL.37s were produced.
However, for the September Campaign, only some 70% of those aircraft were mobilized.
Only 36 PZL.37s were deployed.
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 fighters were a generation 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 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.
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.
Economic base.
Between 1936 and 1939, Poland invested heavily in industrialization of the Centralny Okręg Przemysłowy, chosen for being reasonably far from both the Soviet and German frontiers.
That heavy spending on military industry pushed much of the spending on actual weapons into 1940–42.
Poland had been preparing for defensive war for many years; however, most plans assumed German aggression would not happen before 1942.
Polish military industry development and fortifications were scheduled to be completed in that year, and newer tanks and aircraft were just entering production or would shortly.
Starting in September 1936, France loaned Poland 2.6 billion francs over a 5-year period, which added 12% to the annual Polish military budget.
The Polish defense budget for 1938–39 was 800 million złoty, of which:   Armored force—13.7 million  Artillery—16 million  Air Force—46.3 million  Navy—21.7 million  Cavalry—58 million To raise funds for industrial development, Poland was selling much of the modern equipment it produced; for example, anti-tank guns were sold to Britain and planes were exported to Greece. 
The Invasion of Poland, ' or the Fourth Partition of Poland (Polish: "Kampania wrześniowa" or "Wojna obronna 1939 roku" or "IV rozbiór Polski") in Poland and the Poland Campaign (German: "Polenfeldzug") or Fall Weiss (Case White) in Germany, was an invasion of Poland by Germany, the Soviet Union, and a small Slovak contingent that marked the beginning of World War II in Europe.
The German invasion began on 1 September 1939, one week after the signing of the Molotov–Ribbentrop Pact, while the Soviet invasion commenced on 17 September 1939 following the Molotov-Tōgō agreement which terminated the Nomonhan incident on 16 September 1939.
Polish to Germany forces in the September Campaign: 1,000,000 soldiers 4,300 guns, 880 tanks, 435 aircraft (Poland) to 1,800,000 soldiers, 10,000 guns, 2,800 tanks, 3,000 aircraft (Germany).
A comparison of both armed forces clearly indicates the problems faced by Poland.
Germany had 11 tank divisions compared to Poland’s 1; and Germany four motorised divisions compared to none in Poland; and Germany had 40 infantry divisions compared to Poland’s 30.
An army group led by von Rundstedt attacked from the south while another army group led by von Bock attacked from the north with large mechanised forces.
Before the war, between 1936 and 1939, Poland invested heavily in the 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.
The Polish Army had approximately a million soldiers, but less than half were mobilized by 1 September.
The Polish military had fewer armored forces than the Germans, and these units, dispersed within the infantry, were unable to effectively engage the enemy.
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.
Before the war, in 1939, the Polish Army still had 102 light tanks FT-17, of those 70 in the 2nd armoured battalion in Żurawica and 32 in two Armoured Trains' Units (as armoured draisines), some of these tanks were "iron" FT-17 CWS.
The combat usefulness of FT-17 tanks in 1939 was very limited, since they were very obsolete and extremely slow by these standards and participated in defense of Poland in September 1939, by the 2nd Armoured Battalion formed three light tank companies (numbers: 111, 112, 113), equipped with Renault FT-17 tanks.
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.
During the mobilization in August 1939, the Vickers tanks were used in two light tank companies of Polish only two motorized brigades.
The 11th Armoured Battalion formed the 121st Light Tank Company for the 10th Cavalry Brigade, while the 2nd Armoured Battalion formed the 12th Light Tank Company for the Warsaw Armoured-Motorized Brigade (WBP-M).
On 3 September 1939, the Polish tanks, attacking along Krzeczów W - Skomielna W road, twice repelled the infantry of the 2nd Panzer Division, which was attacking the flank of the 10th Mounted Rifle Rgt.
The second unit to use Vickers tanks was the 12th Light Tank Company of the Warsaw Armoured-Motorized Brigade (WBP-M).
During August and the first two weeks of September 1939, the Brigade was being organized and trained, and stayed on the right bank of the Vistula.
The first combat action, against the German bridgehead over the Vistula near Annopol.
One of the main tank battles was at the Battle of Piotrków Trybunalski a battle which started with the German breakthrough during the Battle of Borowa Gora.
After the German breakthrough at Borowa Gora, the Germans and their tanks and soldiers headed for the Polish town of Piotrków Trybunalski.
German tanks attacked the town, but Polish 155 mm howitzers destroyed several tanks and the Germans fell back, returning again later that day.
The Germans managed to destroy 7 Polish tanks with artillery, but just after, they lost five of their Panzer tanks.
After receiving several more direct hits and losing two more large Panzer tanks, the German tank crews simply ran away.
Polish 7TP tanks pursued and kept beating the rest of the tanks off.
The German soldiers now met the Polish infantry and attacked, but they were repelled by the Polish tanks.
Soon, all the Germans retreated and by the end of September 6, no hostile forces were in Piotrków Trybunalski.
On September 7, Marshal Rydz-Smigly ordered the Polish forces to withdraw.
The core of the Polish force consisted of most of "Prusy" Army's Northern Group.
The army, created as the main operational reserve of Polish commander in chief Marshall Edward Rydz-Śmigły was also the last to be mobilised in the summer of 1939.
Intended as a reserve of Łódź Army and Kraków Army, the Prusy Army was to support its' neighbours and relieve them once the main German attacks are slowed down.
However, the Battle of the Border did not gain the Poles enough time to fully mobilise the reserves.
While most of Polish Army had been successfully mobilised prior to 1 September 1939, on that date many sub-units of Prusy Army were still being formed or transported.
By 4 September 1939, when the German forces broke through the overstretched Polish defences, the Prusy army was far from battle-ready.
Its Northern Group at that date consisted of 29th Infantry Division and Wileńska Cavalry Brigade, with 19th Infantry Division still being formed in the forests to the north-east of Piotrków Trybunalski while the 13th Infantry Division was still waiting for some of its' sub-units near the railway hub of Koluszki and did not become available until September 6.
The army was strengthened by a mobile reserve formed by the 1st Light Tank Battalion (armed with modern 7TP tanks) stationed between Opoczno and Końskie, and the 81st Motorised Sappers Battalion.
Apart from units of the Prusy Army, the Polish side also included a number of smaller units from Łódź Army.
In the city of Piotrków Trybunalski itself the 146th Infantry Regiment was being mobilised for the 44th Reserve Infantry Division and was dispatched to the front as part of an improvised battle group under Col. Ludwik Czyżewski.
In addition, elements of the Wołyńska Cavalry Brigade and the 2nd Legions' Infantry Regiment of the 2nd Legions Infantry Division also took part in the battle as part of Col. Czyżewski's group.
It is unclear how many of the new Polish 9TP tanks were actually produced, although it appears at least 11 9TP tanks were delivered and used by the Polish Army at the start of hostilities as most Polish forces had the 7TP.
The 11 tanks could have been either standard 7TP or 7TP with some of the modifications included, but not all of them.
The tanks of this batch were incorporated in the 2nd Light Tank Company and took part in the fights during the Siege of Warsaw and served with distinction until the capitulation of the city on 27 September 1939.
In September 1939, Polish Army had only 136 7TPs (24 dw, 97 jw and 11 jw produced in September 1939 along with 4 prototypes made of regular plate), which equipped two Polish light tank battalions (each with 49 tanks) and other units.
During Polish Campaign, Polish 7TP Light Tank units put up a valiant defense against the invading German Army in the opening phases and the 7TP proved to be a match for any German Panzer.
The Poles had placed great value on the River Vistula to act as a natural barrier to any form of military advance.
The Germans crossed the river on Day 5 of the attack.
By this time, the Polish air force had been defeated and this had stripped the Polish Army of any form of air cover – it also meant that the Polish tanks and army were easy targets for the Luftwaffe which was free to operate in Poland after September 2.
When the Russians invaded eastern Poland on September 17, the defeat of Poland was sealed.
On September 24, Warsaw was bombed by 1,150 German aircraft.
Ironically, many point to the impact of German tanks during the campaign.
Yet it is known that many of the tanks used during the attack were equipped only with machine guns or small calibre guns rather than cannons as compared to later tank designs.
What did the damage was the constant onslaught of all parts of blitzkrieg, including large numbers of tanks, that never allowed the Polish Army to gather its breath and re-group.
Complete air superiority gave the Germans every opportunity to attack the retreating Polish forces and destroy their tanks.
The Ju 87 Stukas were a constant threat to the Polish tanks and forces, and six Polish divisions trapped by encircling German forces were forced to surrender after a relentless four-day bombardment.
On September 27, Warsaw surrendered.
The Polish military put up a brave fight but they were the first army to feel the full might of the German Blitzkrieg, the same tactic that was to push the British and French armies back to Dunkirk in 1940 and in Poland, tanks versus a primarily non-mechanised army could only lead to one result.
The campaign against Poland ended on 6 October 1939 with Germany and the Soviet Union dividing and annexing the whole of Poland.
Some captured 7TPs were painted in Panzergrau with German markings and were presented during the victory parade in Warsaw on October 8, 1939.