French soldiers keep watch on Colonial Route 4. In 1950, it was a dirt road about 12 feet at the widest and nearly overtaken by vegetation. (CCI, Bridgeman Images)

When the smoke cleared, the French had suffered their greatest colonial defeat since 1749, wrote French historian Bernard Fall.

Gen. Vo Nguyen Giap
Gen. Vo Nguyen Giap

The young soldiers of Gen. Vo Nguyen Giap’s newly formed 308th Division, freshly trained and equipped by the communist Chinese, showed off their skills in stealth operations against the French in May 1950. Four of Giap’s infantry battalions scaled steep limestone heights surrounding the town of Dong Khe in northeast Tonkin, the northernmost region of Vietnam, without being detected even though they were hauling five American-made 75 mm pack howitzers. At dawn on May 25, they opened fire with a devastating sustained barrage on the French defenses and the 800-man garrison, consisting mostly of Moroccan riflemen under French officers.

Giap, commander in chief of communist-led Viet Minh independence fighters at war with colonial ruler France since December 1946, lifted the barrage after two days of shelling. His troops then attacked in human waves, overrunning the base and almost wiping out the remaining defenders, a few of whom escaped into the jungle. At midmorning on May 27, 48 hours after the barrage began, the Viet Minh had seized control of Dong Khe.

The French responded quickly to the May 27 attack, dropping the 3rd Colonial Parachute Battalion onto the overrun base late the same morning and surprising Viet Minh troops engaged in looting. After several hours of heavy fighting, often hand-to-hand, the Viet Minh abandoned the post and melted back into the jungle.

Giap never intended to hold the base. The general had accomplished his objective for now. The May attack was Giap’s last opportunity to season the men of the 308th Division for formidable tasks ahead. He was preparing to unleash a large-scale offensive against six French frontier posts—including Dong Khe—along Colonial Route 4 near the border with China when the monsoon rains ended in late September or early October. Months of arduous preparation lay ahead of Giap.

After the Viet Minh withdrew from Dong Khe, the French commander in chief, Gen. Marcel Carpentier, a total stranger to Indochina, could have avoided another Viet Minh onslaught by evacuating the frontier forts, which contained almost 12,000 French and North African troops, French Foreign Legionnaires, allied Tai tribesmen and camp followers. He had enough time to evacuate them. However, he failed to do so.

Carpentier may have contracted hubris, a disdain for the enemy that infected many French—and later American—officers. They vastly underestimated the fighting capabilities of the enemy while greatly overestimating their own.

In late 1949, Giap ratcheted up pressure on the large French supply convoys trying to navigate Route 4 to reach the forts. The convoys drove into deadly ambushes, roadblocks and blown bridges. The growing presence in southern China of Mao Zedong’s communist forces—recently victorious in the Chinese Civil War against Chiang Kai-shek’s Nationalists—encouraged Giap to attack the Route 4 posts in late 1950.

Giap had spent grueling months in the Viet Bac region, a remote territory in north and northeastern Tonkin where the Viet Minh insurgency was headquartered. He organized his 100,000 main force regulars into six mobile divisions (70 battalions) backed by artillery, much of which consisted of U.S.-made weapons captured from the defeated Chinese Nationalists.

Giap was now ready to give his troops their baptism of fire in conventional warfare. The Viet Minh’s target was the string of isolated Route 4 French forts: Dong Khe, Cao Bang, That Khe, Nam Nung, Tien Yen and Lang Son. Another fortress, Lao Cai, supported by four surrounding forts, was in the Tai Highlands, west of the Red River where it crosses the Chinese border. A decisive Viet Minh victory would clear French forces from all of northern Tonkin east of the Red River, allowing unfettered movement of men and supplies from communist China into the Viet Bac. As a bonus, it would give Giap’s troops a morale-boosting triumph in their first major test on the battlefield.

In May 1949 the French government sent army Chief of Staff Gen. Georges Revers to Tonkin on a fact-finding mission. He recommended that border posts be heavily reinforced or abandoned as soon as safely possible. The French did neither.

After recapturing Route 4 in 1947 during Operation Lea, the French installed permanent garrisons at intervals along the “road”—actually, nothing more than a well-worn, one-lane dirt path, 12-feet wide at its widest and flanked on both sides by heavily forested hills, jungle and jagged limestone peaks. In 1950, Route 4 was controlled by the Viet Minh. The forts were not mutually supportable and could be attacked individually at Giap’s discretion. They were not only vulnerable but also tying down thousands of troops needed in the Red River Delta, where the Viet Minh were adding to the number of villages they controlled.

Giap was never idle during the wet months between campaigning seasons. From 1948 to 1950 he established a logistical system fully capable of supporting his large combined-arms divisions over long distances and periods of time. He was fortunate to have gained a powerful ally in Mao. The fellow communist helped Giap solve his heavy armament and complex supply problems, sent experienced officers to the Viet Bac to act as trainers and mentors, and established a military advisory group at the battalion level and higher to help Giap and his officers plot strategy. The general and his staff spent endless hours preparing for attacks. The infantry used scale models of the targeted forts to practice assaults, day after day. During the coming offensive, Giap never attacked without at least a 3-1 advantage in numbers; at times it was 8-1.

By late 1950 Viet Minh roadblocks, mines and ambushes along Route 4 had inflicted heavy losses in French soldiers and equipment on their way to the big base at Cao Bang, commanded by the “Fighting Legionnaire,” Lt. Col. Marcel Charton. Stymied on the ground, the French began supplying Cao Bang only by air. They evacuated their smaller Route 4 posts, leaving Cao Bang, Lao Cai, That Khe and Dong Khe the only forts still garrisoned upcountry from the regional headquarters at Lang Son. Route 4 had become the deadliest road in Indochina. As the Legionnaires put it, “The Route Coloniale No. 4 is a road than a man travels only one time alive.”

In early September Carpentier announced that the French would attack and capture the town of Thai Nguyen on Colonial Route 3. Afterward, the garrison at Cao Bang would evacuate and walk south on Route 4, leaving artillery and heavy transport behind. Carpentier instructed Charton to conduct his withdrawal with “speed and surprise,” neither of which was remotely possible along Route 4. Thai Nguyen had no tactical connection to the Route 4 forts. Its capture was essentially a publicity stunt to deflect attention from the Cao Bang evacuation.


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