 Several thousands Serb rebels, already under heavy Croatian Ustasha oppression since April 10 and establishment of Independent State of Croatia, managed to hold onto the city for 48 hours before being forced back across river Bosna as German armored units entered Doboj from Derventa/Brod and Tuzla area.In retreating through the streets of Doboj, they were under constant heavy fire from the fortress and had multiple casualties.On the evening of September 9th 1944, in coordinated action, 14th Central-Bosnian Partisan Brigade and 21st Slavonian Partisan Brigade attacked Doboj and took most of the city by the following morning.