Poland

Between 1936 and 1939, Poland invested heavily in industrialization of the Centralny Okręg Przemysłowy. 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 was selling much of the modern equipment it produced. The Polish Army had about a million soldiers but less than half were mobilised by the 1 September. Latecomers sustained significant casualties when public transport became targets of the Luftwaffe. The Polish military had fewer armoured forces than the Germans and, being dispersed within the infantry, were unable to effectively engage the enemy.

Experience in the Polish-Soviet War shaped Polish Army organisational and operational doctrine. Unlike the trench warfare of the First World War, this was a conflict in which the cavalry's mobility played a decisive role. Poland acknowledged the benefits of mobility but was unwilling to invest heavily in the expensive and unproven new inventions to make that a major part of its armed forces. In spite of this, Polish Cavalry brigades were used as a mobile

The Polish Air Force was at a severe disadvantage against the German Luftwaffe although, contrary to popular belief, it was not destroyed on the ground. Although the Polish Air Force lacked modern fighter aircraft its pilots were some of the best trained in the world at that time and had done quite well against the attacking Germans who had numerical and qualitiative airplane superiority, as Poland had only approximately 400 airplanes, including 169 fighters (and another 400 obsolete transport, reconnaissance and training aircraft). Only 36 of them might be considered as modern (PZL 37 Łoś) - the other were far older than their German counterparts e.g. Polish fighters (PZL P.11 - produced in early thirties) were capable only of 350 km/h which is far less than German bombers.

The Polish Navy was a small fleet composed of destroyers, submarines and smaller support vessels. Most Polish surface units followed Operation Peking, leaving Polish ports on August 20, evading German forces and escaping to 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 with much less success. In addition, many ships of the Polish Merchant Navy joined the British merchant fleet and took part in various convoys during the war.