Route Coloniale 4 (RC4, also Highway 4) is a mountain road in Vietnam, bordering the Chinese border from Hanoi to Cao Bang. It is famous for a French military disaster in 1950 in which several units of the French army, including some battalions of the Foreign Legion, were decimated 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 guerilla 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 communist Viet Minh a safe haven for organization and training, as well as an initially sympathetic ally to provide them with arms and logistical support.
General 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.
Battle of Dong Khe
On May 25th 2,500 Viet Minh troops overwhelmed the French fortress at Dong Khé, which lay at the strategic centre 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 May 27 and a company of Legionnaires took charge of the fort.
Meanwhile, the Viet Minh regular army, the Chu Luc, was becoming larger and better trained. 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 September 16 five Viet Minh infantry and one heavy weapon battalions attacked Dong Khé. 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 September 18 the fort was overrun after bitter fighting, and only 12 survivors escaped to the nearby post at That Khé. 140 Legionnaires had been taken the prisoner, the remainder being killed or missing in action.
Battle of That Khe
That Khé was quickly reinforced by the Foreign Legion’s 1st Parachute Battalion (1st BEP), which parachuted in on September 17. 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-Maurice 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 Tho partisans and their families.
Battle of RC4
On September 30 Groupement Bayard set out from That Khe, led by the 1st 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 October 2, 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 October 1; 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 October 5.
Battle of Coc Xa
The French forces were driven into the Coc Xa gorge, where they were completely annihilated by October 7. In an attempt to support the embattled troops the 1st BEP Replacement Company (120 men) had been merged with 280 men from the 3rd BCCP (Bataillon Colonial de Commandos Parachutistes) and were parachuted into That Khe, but were also destroyed. Only 23 survivors of the 1st BEP managed to escape to French lines: it became the first French parachute battalion lost in combat, followed by the 3rd BCCP.
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 October 17 and on October 18 the French command evacuated posts south of Lang Son on RC4. Panic spread in French-controlled Hanoi and there was the 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.
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