(No doubt, the main author of this Lessons Learned report was Colonel Nguyen Van Hieu, the II Corps Chief of Staff, who had planned this operation)
In Southeast Asia, Vietnam is the only country where the annual rainy season occurs at different times in different parts of the country. Whereas pronounced precipitation covers the Mekong River Delta and the Central Highlands from May to October, the bad weather period in the coastal provinces only begins in late September.
The weather diversity has an important effect on military operations. In the coastal zone, intensive rainfall in winter and spring usually causes devastating floods and creates difficulties for friendly activities. On the other hand, the wet and cloudy summer and autumn in the Highlands offer real tactical advantages to the Viet Cong because friendly forces, especially army and air force aviation, are severely limited in their movement and operations.
The Viet Cong regarded the 1965 rainy season not simply as a chance to gain the initiative, but as the opportunity to bring a decisive turn to their aggression. Under the cover of rain, fog, and the jungle canopy, and with massive infiltration from North Vietnam, they believed they could establish a "liberated zone" within South Vietnam to serve both political and morale purposes as a similar move did so successfully at Dien Bien Phu 11 years earlier.
The Highlands were their objective and coordinated activities were conducted to put the whole area under their control and into an economic asphyxia.
To a certain extent, the Viet Cong were successful in cutting off access to the Highlands. The situation reached a crisis when the main supply routes to this area - Highways 14, 19, and 21 - were interdicted by systematic destruction of bridges, frequent ambushes, and intense guerrilla activity (Figure 1).
During June 1965 along Highway 19 (about 180 kilometers long), the population living in resettlement centers and "new life hamlets" were forced to leave their homesteads and evacuate to the district towns of Binh Khe and An Khe.
Life in the chief town of Pleiku itself was no better. While the price of food and commodities rose steadily, in some cases more than doubling in six months, intense Viet Cong activities took place in the vicinity. The town of Le Thanh, 40 kilometers west of Pleiku, was attacked on 1 June, and a few days later the party of the chief of the province was ambushed.
Evacuation and Panic
The scarcity of food and the increasing enemy pressure forced many people to evacuate their families to Saigon. Tension in Pleiku became higher than in the days following the sneak attack on the 2d Corps Advisory Group billets and the 52d Aviation Battalion airfield in February. By the first days of July, the population of Pleiku and Kontum were near panic.
On 15 June, with the destruction of the main bridges on Highway 14, the last ground link from Banmethuot and Saigon to Pleiku and Kontum was cut. The area now depended on air supply to survive. Available aircraft could supply only a fraction of the needs, even when military equipment and supplies to the units stationed in the Highlands were delayed to give first priority to food and medicines.
By early July Highways 1, 11, 14, 19, 20, and 21 were denied to friendly use, and the only link between the Highlands and the coastal area was by air.
The heavy enemy pressure in the Highlands not only affected the people in that remote area, but also had a serious morale effect on the people of the whole country. Something had to be done.
Therein lay the difficulty, because it was not simply a matter of concentrating necessary troops to reopen the highways. The decision had to insure complete success and, at the same time, deny to the Viet Cong the ability to retain the initiative by shifting their activities elsewhere. The decision also had to prevent the Viet Cong from taking advantage of friendly handicaps during the rainy season to apply their favorite and skilled ambush tactics in the rough terrain or to sacrifice their human waves in order to obtain spectacular success as was done at Dien Bien Phu.
Concept of Operation
On 8 July 1965 the 2d Corps command and staff began to plan a large-scale road-clearing operation. The concept of Operation Than Phong was:
D-day was set for 16 July.
Based upon this concept, three guidelines were established:
The first goal was realized by two-phase planning in which only authorized personnel participated. These secret meetings took place as regular staff meetings, and precautions were well kept.
A large diversionary plan had been prepared by all major units available.
The 22d Infantry Division and the 3d Armored Battalion were to reopen Highway 1 from Qui Nhon to Tuy Hoa.
The Airborne 2d Task Force and Regional and Civilian Irregulars Defense Group Forces were to reestablish the district town of Le Thanh, and at North Dak Sut the Marines' Alpha Task Force and the 42d Regiment were to reopen Highway 14. The 20th Engineer Group was to repair the bridge at Le Bac and Interprovincial Route 7 from Phu Bon to Tuy Hoa (Figure 2).
Three Phases
In order to maintain the momentum of the attack and secure complete surprise, the operations were divides into three phases:
It is important to note that all troop movements, their positioning, and the opening of the route actually took place only during five days, from D minus 2 to D plus 2.
The general scheme of maneuver of the main effort of Operation Than Phong was as follows:
By this scheme of maneuver, the most dangerous portion of the route where most enemy ambushes on Highway 19 usually took place was cleared by a coordinated attack with the main effort advancing toward the rear of the enemy.
The task force organization allowed the 2d Corps to deny the enemy possible ambushes by the mobility of its attached armored elements and the protection of artillery fire (Figure 3).
Execution
In addition to large numbers of strike sorties and 66 reconnaissance and escort missions, 30 B-52's pounded the area around the Mang Yang Pass with 500 tons of bombs at 0730 on 17 July.
The task forces were closely controlled in their progress. They retained complete freedom of action, but 2d Corps's planning had compelled them to occupy high grounds along the highway and to move by successive bounds. Although the operation required speed of action, the adoption of that measure of careful prevention proved itself to be more remunerative than that of disentrapment which is apparently economical but actually expensive.
With these tactics, only minor engagements occurred because the enemy had been denied the advantages he had in the past.
While the deployment of forces and adequate tactics forced the Viet Cong to remain nearly inactive and created no problem for the operations, logistic activities met difficulties because of a transportation shortage.
To meet requirements, all vehicles from units stationed at Pleiku and Qui Nhon were concentrated to form a pool to add to the capabilities of the transportation units. This measure, together with the enforcement of a tight daily schedule and strict traffic regulations, allowed within five days (D plus 3 to D plus 7) an initial buildup of 5,365 tons of supplies in Pleiku.
The convoys transfused new life into the Highlands. Along with an immediate drop of 25 to 30 percent in the price of food and commodities, the population regained their feelings of security, confidence, and hope. School-boys in Pleiku voluntarily helped the troops in unloading the cargoes, and people who had started to evacuate now returned to their homesteads.
Following the military convoys, commercial buses could circulate freely and alone, but those carrying rice were restricted to convoys escorted by troops.
Subsequent results at the Duc Co battle (3 to 18 August), the successful reopening of Highway 21 (19 August to 2 September), and the 36-day pursuit and exploitation by the US 1st Cavalry Division at Plei Me redressed the over-all situation in the Highlands.
Major General Vinh Loc
Military Review, April 1966
(Vietnam Center Archive)