The Battle of Route Coloniale 4 (called Chiến dịch Biên giới [Operation Border Zone] in Vietnam) was a battle of the First Indochina War. It took place along Route Coloniale 4 (RC4, also known as Highway 4), a road which was used to supply the French military base at Cao Bang. French military traffic along the road had previously been subject to an ongoing series of ambushes during 1947-1949.The battle lasted from 30 September to 18 October 1950 and resulted in a French defeat.