Repeated Việt Minh ambushes along RC4 near Cao Bằng forced France to overhaul convoy tactics and eventually shift to air supply by 1950.
Key Facts
- Route length (RC4)
- 147 miles miles
- Convoy size (Sept 3, 1949)
- 100 vehicles vehicles
- Convoy distance travelled
- 16 miles (26 km)
- Viet Minh attack on Cao Bằng
- July 25, 1948; held out 3 days
- Ambushes in 1948
- 28
- French survivors found alive
- 4 wounded
By the Numbers
Location
Cause → Event → Consequence
From the outset of the First Indochina War, Việt Minh forces systematically ambushed French military convoys along Route Colonial 4 (RC4), a 147-mile road running along the Vietnam–China border. Despite repeated French operations—including Foreign Legion missions—to reopen the road, ambushes multiplied, reaching 28 incidents in 1948 alone, and Việt Minh battalions seized the post at Lào Cai in early 1949.
On September 3, 1949, a reinforced French convoy of 100 vehicles departed That Khe, travelling 16 miles through infantry screens. Stretched thin at one soldier per vehicle, French troops were struck by automatic weapons fire and shellfire that halted the leading and trailing vehicles and destroyed the convoy's middle section. When French forces reoccupied the surrounding high ground the following day, only four wounded soldiers were found alive.
The disaster compelled France to reform convoy procedures for the remainder of the war: vehicles thereafter moved in small groups of 10–12 under troop security screens and aerial observation. By 1950, ground supply convoys to Cao Bằng were abandoned entirely in favour of air resupply, reflecting how thoroughly the Việt Minh had made RC4 untenable for conventional logistics.
Belligerents & Mobilization Analysis
Side A
1 belligerent
Side B
1 belligerent