Battle of Route Coloniale 4

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. Several units of the French army, including some battalions of the Foreign Legion, were devastated by the Viet Minh and essentially ceased to exist as fighting units.

RC4 in the First Indochina War


During the French Indochina War (1945–1954), French forces attempted to re-establish colonial control of Vietnam, while nationalist forces led by Ho Chi Minh fought for independence. Initially, the Vietnamese guerrilla forces, the Viet Minh, were unsuccessful in dealing with the better -trained and -equipped French forces. Their situation improved in 1949 after the Chinese Communist army of Mao Zedong defeated the Nationalist army led by Chiang Kai-Shek. This gave the Viet Minh forces, now almost completely made up of members of the Vietnam Communist Party, a safe haven for organization and training, as well as an initially sympathetic ally to provide them with arms and logistical support.

Vo Nguyen Giap, the military leader of the Viet Minh, launched an offensive against the French in early 1950. From February to April, his operation Le Hong Phong I raged through the Red River Valley, largely giving the Viet Minh control of northwestern Tonkin, near the Chinese border. The area became a Viet Minh stronghold, except for the RC4 highway.

On 25 May, 2,500 Viet Minh troops overwhelmed the French fortress at Dong Khé, which lay at the strategic center of RC4, thus cutting the supply line between the French positions at Cao Bang and Lang Son. French parachutists retook Dong Khé on the evening of 27 May and a company of Legionnaires took charge of the fort.

Meanwhile, the Viet Minh regular army grew in size and experience. By the beginning of September, it comprised roughly 100,000 combatants in 70 battalions, with another 33 battalions of regional forces (40,000 men) as well as some 60,000 local support personnel. Giap then began harassing French positions along RC4 in northern Vietnam with mines and ambushes. The French responded by dismantling their small posts along the road and concentrating area forces in the fortified positions at Dong Khé and Cao Bang. Giap planned to launch another assault on French positions in operation Le Hong Phong II.

On 16 September, five Viet Minh infantry and one heavy weapons battalions attacked Dong Khe. It was then garrisoned by some 300 French troops comprising the 5th and 6th companies of the 2nd battalion of the 3rd Regiment of the French Foreign Legion (3rd REI). On 18 September, the fort was overrun after bitter fighting, and only 12 survivors escaped to the nearby post at That Khé. 140 Legionnaires had been taken prisoner, the remainder being killed or missing in action.

That Khe was quickly reinforced by the Foreign Legion's 1st Parachute Battalion (1st BEP), which parachuted in on 17 September. The 1st BEP waited at That Khe while a force of French colonial troops, the Moroccan 1st and 11th Tabors, assembled at Lang Son. Designated Groupement Bayard the combined force comprised 3,500 men under the command of Colonel Le Page. The task force launched an intelligence raid, capturing prisoners who said a massive Viet Minh offensive was planned.

Meanwhile General Marcel Carpentier, the commander in chief of French Indochina, decided to evacuate Cao Bang. The commander of the Cao Bang fort, Colonel Charton, was ordered to destroy his heavy equipment and motor transport and evacuate towards Dong Khé. The plan was that Groupement Bayard would fight its way north from That Khe and retake Dong Khé, holding it long enough to link up with the Cao Bang group. This group comprised 2,600 troops and 500 civilians, the latter mostly pro-French Thai partisans and their families.

Battle of RC4
On 30 September, Groupement Bayard set out from That Khe, led by the 1 BEP. However, Giap had concentrated ten battalions around Dong Khé, reinforced by a complete artillery regiment, together with the remaining forces from Le Hong Phong I. The Viet Minh rebuffed the French forces, which were forced to pull back and wait for air support. Le Page renewed the attack on 2 October, pushing west to bypass Dong Khé as Viet Minh numbers were overwhelming.

Meanwhile Colonel Charton's group, led by the 3rd Battalion of 3rd REI, left Cao Bang on 1 October; contrary to orders he took with him his heavy equipment. The group's movement down RC4 was slowed by Viet Minh ambushes. After bitter fighting, they finally abandoned their heavy equipment and linked up with Groupement Bayard in the hills around Dong Khé on 5 October.

The French forces were driven into the Coc Xa gorge, where they were completely annihilated by 7 October. Martin Windrow notes that: Some 130 of the Legion parachute battalion out of the 500 that had jumped emerged from this breakthrough fight; they had only escaped by clambering down lianas shrouding a 75 ft cliff with their wounded tied on their backs. In an attempt to support the embattled troops the 1er BEP Replacement Company (120 men) under Lieutenant Loth had been merged with 268 men from 3e BCCP (Bataillon Colonial de Commandos Parachutistes, Parachute Colonial Commando Battalion) under Captain Cazeaux and they were parachuted into That Khe on 8 October, but over the course of the next week destroyed as well. Only 23 survivors of the 1st BEP, led by Captain Jeanpierre, managed to escape to French lines: it became the first French parachute battalion lost in combat, followed by the 3rd BCCP, of which only 14 soldiers returned unscathed.

Aftermath
Of the more than 6,000 French soldiers and civilians involved in the operation, only 700 reached French lines. Lang Son, the next French base to the south, was abandoned on 17 October and on 18 October the French command evacuated posts south of Lang Son on RC4. Panic spread in French-controlled Hanoi and there was talk of an evacuation. Ultimately, however, General Jean de Lattre de Tassigny replaced Carpentier as commander in chief of French Indochina in late 1950 and restored French morale.