1 September 1939 over Warsaw - The first air battle of WW2
http://www.elknet.pl/acestory/1sept/1sept.htm
…The first Polish pilot to engage the enemy formation was from the section led by Lieutenant (Lt.) Aleksander Gabszewicz, the tactical officer of IV/1 Squadron. After machine-gun fire from both Gabszewicz and Corporal Andrzej Niewiara, one of the damaged He 111s came down in a northerly direction and soon crashed during an emergency landing, hitting one of its wing in a tree. …