Key Facts
- Duration
- October 1947 – September 3, 1949
- Route contested
- Route Coloniale 4 (RC4), ~147 miles
- Ambushes in 1948 alone
- 28
- Final convoy size
- 100 vehicles departing That Khe
- Distance of final convoy
- 16 miles (26 km)
- Survivors found after final ambush
- 4 French wounded found alive
Strategic Narrative Overview
French attempts to secure RC4 included increasingly large relief operations, among them a costly Foreign Legion mission in February 1948. The Cao Bằng post itself was attacked in July 1948, holding out for three days against two Việt Minh battalions. In February 1949, five Việt Minh battalions seized Lào Cai, and ambushes continued through the monsoon season, culminating in a devastating attack on a 100-vehicle convoy on September 3, 1949, that destroyed the middle section of the column.
01 / The Origins
From the outset of the First Indochina War, the French garrison at Cao Bằng depended on a vulnerable 147-mile supply route along the Vietnam–China border known as Route Coloniale 4. The Việt Minh exploited this geography, launching repeated ambushes against French convoys moving through mountainous terrain from the Gulf of Tonkin, steadily escalating pressure on French forces trying to maintain their northern outposts.
03 / The Outcome
The September 1949 ambush left only four French wounded found alive the following day. The campaign forced a fundamental change in French logistics: convoys were reduced to 10–12 vehicles travelling between posts under infantry screens and air observation. By 1950, road supply to Cao Bằng was abandoned altogether in favour of aerial resupply, reflecting French inability to hold RC4.
Belligerents & Mobilization Analysis
Side A
1 belligerent
Side B
1 belligerent
Kinetic Engagement Axis
Scroll horizontally to view full axis. Events plotted relatively.