The French route security approach was based upon numerous fortified posts, intended to form a string of strong points that could control the LOCs throughout the nation, thus permitting French authority to extend into the adjacent villages and countryside. Hundreds of these posts were constructed “in a sweeping semicircle, with an overlapping radius of fire, from pillboxes manned by ten men to elaborate emplacements with artillery and tanks.” The number of these fortified posts was impressive. To safeguard the harbor region around Haiphong in northern Vietnam alone, within a single year 1,200 separate concrete blockhouses were built. A French historian noted regarding the construction of these fortifications: “These constructions, surrounded by barbed wire…differed in size, location and materials, but all had a surrounding wall, a corner blockhouse armed with machine guns, a watchtower, and a French flag flying from the flagstaff. A young officer or [NCO] commanded a few Europeans or Africans or more frequently some Vietnamese, the defenders of such small, jerry-built forts.” Roger Trinquier, a French officer with experience in Indochina, was highly critical of these posts:
…military outposts rarely achieve the hoped-for results, and then usually by accident. Outposts are usually placed at communications junctions that must be held to secure heavy equipment. They cause the guerillas no trouble because there is no need to take them. Armed bands can freely circulate in the large areas between outposts, and can organize and control the population without interference. A few cleverly planned terrorist attacks can suffice to subject the inhabitants to their will. The disposition of the outposts is an open book to our enemies, who observe them at their leisure. They miss nothing. The only usefulness of the outposts is the obligation they create for us. To maintain them forces us to open and keep up roads, to protect supply convoys during the course of long hauls, and in general to carry on military activity in which we would not indulge if it were not for the outposts.
These isolated French posts were extremely vulnerable. Night attacks were routine, and even if not pressed by the Viet Mihn to overrun the post, the nocturnal raids served to intimidate and threaten the local populace. Renowned Indochina historian Bernard Fall described how even an unsuccessful attack on these posts served to isolate it from the Vietnamese population, “The post had lost its usefulness as a link in the chain of forts…as an obstacle to Communist operations in the area, and most importantly, as a symbol of French authority. In a very real sense, it had become non-existent.” A French sergeant who commanded such a garrison echoed: “There were times when we were so discouraged that we felt like giving up completely. Posts were constantly being attacked, roads were always being blocked, convoys always had to have an escort, attempts were made on the lives of isolated soldiers, there was gunfire in all directions every night, and to cap it all, France was completely indifferent to the situation.”
In short order, the Viet Mihn became masters of raids upon French outposts, and ambushes against the French LOCs. They specialized in infiltration that effectively employed cover and concealment; maximized the use of camouflage; established a highly effective intelligence gathering system such that French movements rarely surprised them; and aggressively employed overwhelming firepower in ambushes and attacks. They also made considerable use of mines and what would be later known as Improvised Explosive Devices (IEDs), and when those were not available they routinely blocked LOCs with physical obstacles such as boulders or ditches. Some major bridges were demolished, and rebuilt by the overworked French engineers, no less than seven times during the course of the war. So effective were these actions executed against the roadway that the French called the war “la sale guerre” (the dirty war), to highlight how ambushes, mines and IEDs were so constant a component of their daily existence.
The Vietnamese became experts at the creation and employment of anti-vehicle and anti-personnel mines. A modern historian has observed that they were fashioned “from unexploded French shells and bombs which had been courageously recovered and ingeniously re-fused, Viet Minh sappers also lifed and relaid French mines sown to protect forts. Anti-personnel booby-traps were rigged with grenades and tripwires- or simply but horribly- with panji stakes, bamboo or barbed iron spikes.” These proved terrifyingly effective. In the Mekong Delta, in six months between September 1953 and February 1954, 75 percent of all French deaths and 56 percent of all their wounds would be caused by mines.
The Viet Minh ambushes were typically executed by a pair of “hand-triggered” mines [IEDs] that destroyed the lead and rear convoy vehicles, and thus trapped the convoy within the kill zone. Numerous machine guns and 75mm recoilless rifles swept the kill zone with intensive fire. Covering elements secured both flanks of the ambush. They preferred a classic “L” shaped ambush when the terrain supported it, such that any French troops that survived the initial blast of gunfire found themselves facing enfilading fire from two directions. Anti-personnel and anti-vehicle mines were planted to prevent the French from maneuvering to the opposite side or flanks of the Vietnamese forces.Mortars were located in the rear of the ambush to provide effective fire support, and observation of the LOC and entire ambush area was established. By 1954, nearly all Vietnamese ambushes were controlled by radio. The entire ambush would be concealed in the thick jungle. In effect, they massed a superior force in a battle location of their own selection and timing, and then employed overwhelming firepower to destroy the French convoy.
Complicating the French defensive scenario was that nearly all of the LOCs in Indochina were crude dirt roads over which travel was slow and uncertain, that could be easily mined or obstructed; and that the dense jungle vegetation nearly universally extended right to the edges of the road. A modern historian has assessed of this road network: “For most of their length many of the proudly named ‘Routes Coloniales’ [R.C.] and ‘Routes Provinciales’ were unsurfaced lanes perhaps twelve feet wide; in highland valleys the arching bamboo turned them into tunnels, on the slopes the jungle scraped the sides of passing trucks, and in the mountains they crept precariously along ledges between sheer rock faces and yawning drops.” Even one of the best maintained major highways in northern Vietnam was described by one highly-experienced international automobile traveler as: “a wide, badly paved highway, skirting the railroad.” The dense jungles, rugged terrain and limited road network facilitated the Viet Mihn infiltration and ambushes.
Typical of the successes of these ambushes, in December 1953 a battalion of French paratroopers was surprised as they performed a strong patrol from the fortified base of Dien Bien Phu. When the ambush was initiated by “murderously accurate mortar and grenade launcher fire” the “lead platoon was virtually wiped out within a matter of seconds.”Such effectively executed ambushes along the French LOCs presented a formidable opposition to the French strategy of posts and roads.
Initially, the Viet Mihn was a classic guerilla or partisan effort, with relatively small forces, armed with limited numbers of generally obsolete pre-WWII French weapons and equipment salvaged from the French colonial period, heavily used weaponry consisting of American arms provided to them for fighting against the Japanese, and whatever modern arms and supplies that they could seize from the French garrisons. However, the Viet Minh began to continuously garner strength and organization. By the Battle of Dien Bien Phu in 1954, the Viet Minh operated a modern army organized into divisions; coordinated their maneuvers using contemporary communications equipment; employed heavy weaponry whose artillery was in fact superior to the French; established a carefully integrated and effective air defense system; and supported their operations with a sophisticated logistical system that employed everything from porters and bicycles to newly manufactured Chinese heavy cargo trucks, all directed by a cohesive national military and political leadership.