Shortly after the completion of Operation BIRMINGHAM in May 1966, General William C. Westmoreland, Commander, U.S. Military Assistance Command, Vietnam, directed Lieutenant General Jonathan O. Seaman, Commanding General, II Field Force, Vietnam, to plan an operation for War Zone C in northern Tay Ninh Province to start soon after the Christmas and New Year stand downs of 1966- 67. (Map 5) He further indicated that it should be a "big operation." Over the next several months the operation, to be known as JUNCTION CITY, was planned. As approved by General Westmoreland, the operation was to start on 8 January 1967, was to be multidivisional, and was to include a parachute assault. The operation to commence on 8 January would not be JUNTION CITY: the preemptor was to be known as CEDAR FALLS.
As II Field Force troop strength built up in 1966 and it became more capable of attacking the enemy in longtime havens, General Seaman's headquarters was considering the possibility of a powerful strike into the Iron Triangle. The Iron Triangle is generally defined on the southwest by the Saigon River, on the east by the Thi Tinh River, and on the north by a line running west from Ben Cat to the town of Ben Suc on the Saigon River. To the north lies the Thanh Dien Forestry Reserve. The Iron Triangle has been characterized as a dagger pointed at Saigon and, being only twenty kilometers away, was the enemy's largest haven close to that city. The area was heavily fortified and known to contain the Viet Cong headquarters for Military Region IV which directed military, political, and terrorist activities in the Saigon-Gia Dinh capital region complex. Viet Cong control of the Iron Triangle permitted the enemy forces to dominate key transportation routes in the surrounding area. This important center for controlling and supporting enemy operations had to be attacked decisively and in force if the attack were to succeed in rupturing and neutralizing the control structure.
At a planning meeting in September 1966 General Seaman discussed the possibility of an operation in the triangle with General Westmoreland, who suggested a coordinated operation with forces
on both sides of the Saigon River. He envisioned troops moving into position on one side of the river to form an anvil followed by a rapid move from the other side to hammer the enemy against the anvil. Discussion also turned to the need for extensive clearing to strip the area and deprive the enemy of concealment. By November General Seaman's headquarters was planning not only for Operation Junction City but also for Cedar Falls. Intelligence collection was directed at both operations.
A new approach to assigning intelligence collection responsibilities in III Corps had been taken with the publication of a II Field Force, Vietnam, intelligence collection plan. The plan assigned specific intelligence collection areas, tasks, and responsibilities to U.S. and allied units within the III Corps area; the objective was a closely integrated and coordinated effort by U.S. and allied agencies. Unit collection responsibilities were assigned on the basis of geographic areas. Close liaison was effected between U.S. and allied units from division through battalion level and between U.S. advisers and corresponding commanders of South Vietnamese Army units or province and district chiefs. The plan was designed to provide for the collection of maximum information with minimum duplication of effort.
A step was also taken to improve the intelligence collection effort through the establishment of a source control program in the III Corps area. When fully implemented, this program administratively controlled and identified confidential informants and sources, assisted in their evaluation, prevented utilization of each source by more than one agency and avoided employment of unreliable agents.
Operation Cedar Falls was the first large scale operation to benefit from "pattern activity analysis," a system begun in mid 1966. This procedure consisted of detailed plotting on maps of information on enemy activity obtained from a variety of sources over an extended period of time. As more data were plotted, patterns of activity and locations emerged. It thereby became possible to focus prime attention on those areas of intensive or unusual activity.
Aerial observation and photography, sensors, patrol reports, infrared devices, sampan traffic counts, enemy probes of Regional and Popular Forces posts, agent reports, civilian movement reports, reports of increased antiaircraft fire, disclosures of caches (and the amount and nature of the material in them), and captured documents-these sources and more revealed much about enemy intentions. Increases in road ambushes or bridge destruction
usually meant that the Viet Cong intended to attack in a location where denial of the roads would aid the enemy. Some idea of the enemy's intent could be determined by checking even the amount of wood shipped into an area for making caskets or the number of civilians impressed as porters. The extent and nature of the enemy's own intelligence gathering revealed much about his intentions and even the size of the operation he was planning.
Detailed plotting of all this information and careful analysis of the patterns enabled U.S. forces to launch spoiling attacks both with ground troops and with massive air strikes. Where no pronounced pattern developed in an area, efforts were concentrated elsewhere, thereby conserving forces. Pattern activity analysis was invaluable in developing broad long-range direction of military operations, while at lower echelons it provided commanders a basis for planning day-by-day operations.
The excellence of the intelligence effort was vividly demonstrated by the results achieved. A comparison of installations discovered during Operation CEDAR FALLS with order-of-battle intelligence holdings collected before the operation disclosed a high degree of correlation. For example, of 177 separate enemy facilities found by the 11th Armored Cavalry Regiment, 156, or 88.1 percent, were located within 500 meters of the locations previously reported. The average distance was about 200 meters.
Intelligence information prompted General Seaman to recommend that Operation CEDAR FALLS precede Junction City. General Seaman related the events surrounding the change as follows:
In early December, if I recall correctly, I received a telephone call from [Brigadier] General [Joseph A.] McChristian, (Assistant Chief of Staff, Intelligence [J-2], MACV) saying that he would like to come out and brief me on some intelligence information he had concerning the III Corps Tactical Zone. He came out with several young MI (Military Intelligence) lieutenants who had been in some building in Saigon poring over (special) research reports, clandestine reports, and everything else available. The briefing lasted a couple of hours and was a most convincing presentation in that they had a pretty good idea where Military Region IV headquarters was, plus some of the support elements of Military Region IV. General McChristian said he wanted to bring this to my attention for whatever I felt should be done. I did a lot of thinking about all this and was convinced that he had some good solid, sound information. I called my staff in and told them to prepare plans for an operation to seal off the southwest side of the Saigon River and the Iron Triangle with the objective of seeing what we could find with respect to Military Region IV. We came up with a plan of operation that, to me, was pretty sound. I asked General Westmoreland to come to my headquarters so that I could brief him on a concept of operations for "Cedar Falls." We had developed a good cover plan so that we
wouldn't compromise the operation. I was going to propose to him that we postpone "Junction City" for two main reasons.
First, I felt that the intelligence information we received from General McChristian and his people was so good that we had to capitalize on it. Secondly, the 9th Division was on its way from Fort Riley and would arrive in theater in December and early January.
So, I felt that if we postponed "Junction City" for a month or a little more, this would give me another division I could use to take over some of the other missions that were going on. Remember, we didn't conduct just one operation at a time. . . . With those two facts in mind; intelligence, and that the 9th Division was on its way over, I felt that there was a great advantage in postponing "Junction City."
General Westmoreland was briefed on CEDAR FALLS; the advantages and disadvantages were weighed and the decision made: Operation CEDAR FALLS, rather than JUNCTION CITY, would begin on 8 January 1967. The mission: II Field Force, Vietnam, attacks the Iron Triangle and the Thanh Dien Forestry Reserve to destroy enemy forces, infrastructure, installations, and Military Region IV headquarters; evacuates civilian population; and establishes the Iron Triangle as a specified strike zone to preclude its further use as a support base for Viet Cong operations.
General Seaman furnished further planning guidance: the Iron Triangle area was to be attacked violently and decisively with all forces available in a "hammer and anvil" operation. Deceptive deployments on seemingly routine operations would preposition the forces. The anvil would be positioned first and the hammer then swung through the Iron Triangle. The objective area was to be sealed tightly throughout the operation to prevent enemy escape. The triangle itself was to be scoured for enemy installations, cleared of all civilians, stripped of concealment, and declared a specified strike zone. The destruction of the enemy's Military Region IV headquarters was the principal objective of the operation. (Map 6)
In addition to the Military Region IV headquarters, the other Viet Cong units in the area were suspected to be the 272d Regiment, the 1st and 7th Battalions of Military Region IV under the 165th Viet Cong Regiment, the Phu Loi Local Force Battalion, plus three local force companies. (Although the suspected location of the 272d Regiment presented a threat during the initial stages of the operation, this unit displaced to the north as the operation progressed.) Other intelligence sources indicated the 2d, 3d, and 8th Battalions of the 165th Viet Cong Regiment might also be encountered.
The Thanh Dien forest and the Iron Triangle were known to
contain strongly fortified positions with the routes of approach mined and booby trapped. The terrain in the area consists of dense forests and wet, open rice lands. Cover in the rice paddies, marshes, and swamps is generally limited to road embankments and dikes. Fields of fire are poor in the forests. Vehicle movement is restricted to existing roads and some trails. What few slopes exist are very gentle; the highest points in the area do not exceed forty meters.
The weather for Cedar Falls was most favorable during January when the northeast monsoon develops to its fullest, leaving the interior regions of the III Corps area with relatively clear skies and little precipitation. Except for periods of early morning fog and occasional morning and afternoon rain showers, cloud ceilings are unlimited and the visibility is excellent. The temperature varies from a low of 59 ° to a high of 95 °.
The deception planned in positioning the various units was involved and critical. The 11th Armored Cavalry Regiment was to come from Xuan Loc, 100 kilometers to the east, and the 173d Air-
borne Brigade was operating between Ben Cat and Phuoc Vinh. Elements of the 25th Infantry Division and 196th Light Infantry Brigade were to move from the areas of Cu Chi, to the south, and Tay Ninh city, some sixty kilometers to the northwest. The 1st Infantry Division elements were to be air transported to complete the seal and invade the area. Numerous small-scale movements under the guise of local operations would position other forces.
From the first planning conference, strict security measures were enforced to prevent disclosure of the operation. The planning group was held to a minimum within II Field Force headquarters and, wherever possible, preparations were made without specifically identifying them with CEDAR FALLS. All commanders were instructed on 19 December 1966 to minimize helicopter operations during January. Even the plan for the unprecedented mass evacuation of civilians from the area was not disclosed before the operation. Planning for the transportation and housing of refugees was coordinated only with Mr. John Vann, director of Region III's Office of Civil Operations. Although supplies were earmarked for shipment to a refugee relocation center at Phu Cuong, no construction or stocking was started until Cedar Falls had commenced. General Seaman personally briefed the commanding general of the South Vietnamese III Corps on D minus 2, 6 January 1967. South Vietnamese troop participation was approved at that time with government forces assigned the missions of supporting American blocking forces, of securing and transporting civilian evacuees, and of supporting security forces in the An Loc and Quan Loi areas. The Vietnamese III Corps commander assisted in maintaining security by restricting dissemination of information on the operation.
CEDAR FALLS was to be conducted in two distinct phases. Phase I, 5-8 January, consisted of positioning units on the flanks of the Iron Triangle-Thanh Dien forest area. D-day was set for 8 January when an air assault on Ben Suc would take place. Ben Suc was to be sealed, searched, and, after evacuation of its inhabitants and their possessions, destroyed. Phase II of the operation was to start on 9 January with an armored force attacking west from the vicinity of Ben Cat to penetrate the Iron Triangle. Simultaneously, air assaults in an arc around the Thanh Dien forest from Ben Cat to Ben Suc would complete the northern portion of the encirclement of the triangle. Forces would attack south through the entire objective area to the confluence of the Saigon and Thi Tinh Rivers. All civilians were to be evacuated from the area which would be cleared and the tunnels destroyed. Phase II of Operation CEDAR FALLS was planned to last from two to three weeks.
The task organization under II Field Force consisted of three divisions: the 25th Infantry Division under the command of Major General Frederick C. Weyand; the 1st Infantry Division commanded by Major General William E. DePuy; and the South Vietnamese 5th Infantry Division, Brigadier General Phan Quoc Thuan commanding. Forces supporting the operation were the 7th Air Force; 1st Logistical Command; 3d Tactical Fighter Wing; II Field Force, Vietnam, Artillery; the 12th Combat Aviation Group; and the 79th Engineer Group. South Vietnamese supporting forces included the 3d Riverine Company (Navy), the 30th River Assault Group (Navy), and three Regional Forces boat companies.
CEDAR FALLS was to be the largest and most significant operation to this point in the war.
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