This combination Cause_to_amalgamate proved fatal for the bases ' defenses , culminating Self_motion in a decisive French defeat Conquering at the Battle of Dien Bien Phu .

From then on , the French focused Aiming on creating Creating strong fortified positions , against which Viet Minh General Giáp could pit his forces , culminating in Operation Castor and the Battle of Dien Bien Phu .

The main US Army operation took place Process_start in an area about north of Bien Hoa , where the US 1st Battalion , 503rd Infantry Regiment ( 1/503 ) , 173rd Airborne Brigade conducted Action a helicopter assault on an LZ northwest of the Dong Nai River and Song Be River .