The film is a propaganda movie and contains deliberate errors. A scene, in which a bomber crew saves a column of German-nation refugees escorted by a Polish policeman, is a fiction - in reality, during the Polish campaign, German aircraft crews often met columns of Polish refugees, and they often strafed them.
In September 1939 the only fighter type available to the Polish Air Force was the gull-winged PZL-P.11c. No captured examples were available for the air combat scenes at the time of shooting the film so another captured type that was available in quantity was used: The Czechoslovak Avia B.534. This was a biplane, so anyone with a minimum of knowledge of aircraft could spot the historical inaccuracy..