Known as the battle of Le Hong Phong II to the Vietnamese or Route coloniale 4 to the French, the battle of Cao Bang in October 1950 was linked to the rapidly changing international situation symbolized by the creation of the People’s Republic of China (PRC) in October 1949. In January 1950, the PRC officially recognized the Democratic Republic of Vietnam (DRV). The Soviet Union and the rest of the communist camp followed suit. From May 1950, Chinese military aid and advisors began to cross into DRV territory. This combined Chinese military and diplomatic support effectively internationalized the Franco-Vietnamese war and changed the military nature of the conflict.
For the DRV, it was vital that a large swath of the northern border be opened in order to link the DRV directly to the communist bloc stretching from eastern Europe to southern China. On 7 February 1950, hardly a week after Moscow recognized the DRV, the Vietnamese army began operation Le Hong Phong I in an attempt to take control of Tai regions in northwestern Vietnam, and thereby link up with the Chinese in Yunnan province. It was a failure.
In consultation with Chinese advisors such as Chen Geng, General Vo Nguyen Giap began preparations to attack the French in the area of Lang Son and Cao Bang in order to create an opening further to the east. Thanks to the affaire des généraux, Chinese and Vietnamese strategists knew that General Georges Revers, chief of the Combined Chiefs of Staff for the French Army, had made a fact-finding mission to Indochina in mid-1949 from which he had concluded that the French should not try to hold the northern border against a potential Chinese attack and should withdraw troops from Cao Bang and Lang Son. Rather than directly attacking French border posts in these two areas, Vo Nguyen Giap decided to wait until the French began withdrawing along vulnerable, narrow roads favorable to a Vietnamese attack.
When the French finally began to withdraw their troops on 3 October 1950 in two separate columns, Vo Nguyen Giap and Chen Geng ordered Vietnamese troops to attack the main French column as it withdrew to the east along Route Coloniale 4 (RC4). Giap threw artillery and two regiments of the 308th division against the retreating troops. French efforts to relieve the column from Dong Khe and That Khe proved futile given the combination of the inhospitable terrain and the intensity of the Vietnamese attacks. Within two weeks, the DRV scored its first major battle victory over the French. The French lost some 7,000 men in this debacle, most of whom were taken prisoners by the Vietnamese army and marched off to camps. From this point, Chinese aid more easily entered DRV territory. The extension of the railway from Nanning to the border at Cao Bang only facilitated this process. This battle victory over the French emboldened the Vietnamese as Vo Nguyen Giap moved on plans for a General Counter Offensive. Within months the Vietnamese general was prepared to attack the delta.
At the international level, the French loss at Cao Bang coincided with the Korean War and the entry of Chinese troops into that war. The French and the Americans began to see the wars in Indochina and Korea as part of the same front designed to hold the line against Chinese communist expansion.
While many French strategists would turn to the United States for increased aid, others began to propose alternative solutions for ending the war. During a parliamentary debate on Cao Bang on 19 October 1950, the French Deputy Pierre Mendès France argued that the intensification of the Indochina War at Cao Bang had also coincided with the Allied decision to rearm West Germany. The French could not commit the increased numbers of troops and material needed to win in Indochina without undermining its ability to meet its North Atlantic Treaty Organization commitments and invest in an army capable of matching that of the West Germans. Mendès France said that either the French renew the draft, increase taxes and decolonize fully the Associated States of Indochina in order to win or else they should seek an honorable, negotiated solution to the war. Economically, he argued, the French could not operate on these two fronts simultaneously. The center right government of the time, the Mouvement républicain populaire, preferred to carry on without resolving the problem of financing a war in Indochina and making good on military commitments to the defense of Western Europe. It would take another three years before Mendès France got his chance to end the war along the lines he set out during the Cao Bang disaster of October 1950. Cao Bang had effectively made it clear that a new more intensive and expensive stage in the war had begun. See also AID, AMERICAN; AID, CHINESE; EMILE BOLLAERT; EUROPEAN DEFENSE COMMUNITY; FINANCIAL COST OF INDOCHINA WAR.