Article: Invasion of Poland
Section: Poland

Question: What did Poland heavily invest in between 1936 and 1939?

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.