9 September in military history: the Battles of Krbava Field, 1493, and the Bzura, 1939

An Ottoman force under Hadum Jakub Pasha destroyed the army of the Croatian ban Emerik Derenčin on Krbava Field, below the castle of Udbina. Derenčin had chosen to fight on the open field; he was taken prisoner and his son was killed.

Bishop Juraj Divnić wrote that 13,000 men were partly captured, partly killed. The chronicler Ivan Tomašić wrote that more than 13,000 Christians fell. The pilgrim Jan Hasištejnský heard of about 70 priests and monks and 10,000 others killed and up to 1,500 captured, and the annals of Thann in Alsace give about 5,000 dead.

According to the Hrvatski biografski leksikon he refused to convert to Islam and died in prison at Kara Hisar-i Sahib near Bursa a few months after the battle.

The historian Mariusz Niestrawski and the Poznań Army Museum date the start of the battle to 9 September; Niestrawski opens it with the Polish attack. Robert M. Kennedy's US Army study, which cites a German war diary, records that the German 30th Infantry Division reported itself under heavy attack at noon on 10 September. The first date marks the launch of the attack, the second the German report of it.

The Polish forces were encircled. The Deutsches Historisches Museum dates their surrender to 19 September and counts 170,000 prisoners; on 20 September the Associated Press reported from Berlin that the number of captives was 105,000 and still growing, and the Poznań Army Museum ends the battle on 22 September.