For two years, the French bided their time, staking out an outpost line along Route Coloniale4 (RC 4) on the Chinese border, securing the allegiance of Tai tribes in the north, obtaining the cooperation of the Cao Dai and Hoa Hao religious sects in the south and engaging in more or less effective pacification operations in the Mekong and Red River deltas. They did not grant meaningful power to the anti-communist nationalists, but clung instead to Bao Dai. Manipulated by the Japanese and humiliated by Ho, Bao Dai was demoralized and corrupt, but made a compliant figurehead behind whom French administrators and commercial interests could pursue business as usual. Then, in December of 1949, Mao Tse-tung's victorious Chinese communists arrived at the border and the strategic equation changed dramatically. In the name of revolutionary solidarity, Mao provided the Vietminh with base camps in China and with American arms and equipment captured from the nationalists. The Vietminh built up their guerrilla cadres and trained and resupplied their main force units. In October of 1950 they struck, collapsing the outpost chain along RC 4 in the greatest French colonial defeat since the loss of Canada to Britain in 1763.
French panic was stopped by the arrival of General Jean de Lattre de Tassigny, a remarkable leader and arguably France's best general of the war. De Lattre cancelled an evacuation of French noncombatants from Tonkin, purged incompetent officers and inspired the rest; he began the construction of a series of defensive positions, the de Lattre Line, around the all-important Red River Delta, to free his mobile reserves for offensive operations and he braced himself for the struggle to come. He did not have long to wait; in January of 1951, Giap launched his forces, now organized in divisions, against the Red River Delta in a series of massive attacks which continued until June. It was one of Giap's few miscalculations: the French fought well and the Vietminh lost heavily, not only in the Tonkin where the Catholics sided with the French, but also in Cochinchina where a sacrificial diversionary offensive effectively eliminated the mostly non-communist Vietminh. Having stopped the Vietminh divisions, de Lattre went over to the offensive, launching his forces against the town of Hoa Binh south of the Red River Delta in mid-November. At first the French were successful; paratroops quickly seized the town and linked up with armored forces driving southwest from the delta down RC 6 and with a riverine force of gunboats and landing craft pressing down the Black River from the north. Hoa Binh was the capital of the Muong Tribe, who were friendly to the French, and the move seemed astute politically, but things quickly turned sour. Giap refused to give battle and the Vietminh melted away, only to reappear in carefully planned ambushes that took an increasingly heavy French toll as the months wore on. In January1952, the French, with little to show for their losses, had to withdraw; by the end of February they were back inside the de Lattre Line. In the meantime, de Lattre himself was evacuated to France, terminally ill with cancer. He died weeks before the final French withdrawal.
The Hoa Binh offensive was the high point of French military fortunes. With the onset of the dry monsoon in October, the Vietminh emerged from their base areas in the Bac Viet and crossed the upper Red River to invade the Tai highlands. The Tai tribes had rallied to the French in 1947 and their allegiance was one of the few French political successes, but little had been done to capitalize on it and within weeks Giap's divisions had swept it away. A French counteroffensive against communist supply lines northwest of the Red River Delta in November penetrated 120 miles into Vietminh territory and captured significant amounts of supplies, including Soviet-supplied trucks, but it failed to distract Giap from his prize. As with Hoa Binh, the Vietminh refused to stand and fight; initially easy French gains were followed by increasingly severe ambushes and the French were back to their start line within a month. It had been an exercise in futility.
Meanwhile, and of more pressing concern to the French high command, the Vietminh pressed on intoLaos, seizing Thakekon the Thai border and threatening the Royal capital of Luang Prabang. Luang Prabang did not fall, saved by the onset of the wet monsoon in late April, but it was a near thing and a major embarrassment for the French, for whom tranquil Laos had been one of the few bright spots in a gloomy picture.
Several weeks later, a new commander in chief, Lieutenant General Henri Navarre, arrived from Paris. Intelligent and energetic, though with a distant, even cold personality-an associate described him as "feline" in temperament - Navarre understood that time was running out for the French. Casualties among the regular forces had caused little outcry, but expenditures on the war continued to mount with little to show in return and French political patience was running thin. Navarre consulted with his theater commander in Tonkin, Major General Rene Cogny, and resolved to stake everything on a final roll of the dice, confident that if he raised the stakes high enough he could draw Giap's divisions into battle and crush them with superior firepower. He predicted victory in words that were to haunt his American successors: "Now we can see it clearly -like light at the end of a tunnel." Navarre's plan was calculated to solve several problems at once. He would insert a major French force deep within Vietminh territory by air, blocking the invasion route to Laos, providing a base to support partisan operations behind communist lines and forcing Giap to give battle. The location which he and Cogny selected for their airhead was a former provincial seat in a river valley near the Laotian border, Dien Bien Phu. To command the operation, Navarre selected Colonel Christian de Castries a dashing, highly decorated cavalryman with a brilliant record, seemingly the ideal choice to lead the slashing raids into communist territory which Navarre and Cogny envisioned.