During the interwar period, the Second Polish Republic wanted to expand its air force (especially in the 1930s), but due to the difficult budget situation and relatively weak industrial base, these efforts did not bring the desired effect. Thus, at the start of the September campaign in 1939, the Polish aviation had a relatively small number of modern machines (e.g. PZL P.37 Łoś), but the majority of its aircraft were outdated in 1939 (e.g. PZL P.7 or P. 11), giving way to their German counterparts. Moreover, the Polish aviation was numerically weak - it was able to deploy only 392 operational combat aircraft at the beginning of the September campaign. It should also be added that it lacked communication and communication (insufficient number of radio stations), as well as did not have modern means of air attack recognition. Despite all these shortcomings, the Polish air force was able to inflict relatively large losses on the Luftwaffe and, contrary to popular opinion, it was not crashed on September 1 at field airports. This is a huge merit of the Polish pilots who - as it turned out - were well trained and were not inferior in their skills to their German counterparts. Many of them broke through - after the defeat in the September campaign - to France, and then to Great Britain, where they were part of Polish fighter and bomber squadrons, among which 303 Squadron and its achievements during the Battle of Britain became legendary.