Riverine Operations and the Cambodian Incursion

General Creighton Abrams's assumption of command of the U.S. forces in Vietnam in July 1968 presaged major changes in the direction of American efforts there. These changes came in no small part from President Johnson's decision in March not to enter the presidential race and a resulting push toward a negotiated peace and American withdrawal.

By and large this push posed no problems in division-level communications that had not appeared in earlier tactical operations. Two exceptions were riverine operations in the rice-rich delta region south of Saigon and incursion into Cambodia. Both called for exceptional ingenuity and perseverance from tactical communicators.

Riverine Operations

The Mobile Riverine Force was conducting Operation CORONADO I in the delta region as the third year of combat began. The 2d Brigade of the 9th Infantry Division, commanded by Colonel William B. Fulton, combined with the U.S. Navy's River Assault Flotilla One, made up the force. The 9th Division established an advance command post at Dong Tam from which the assistant division commander normally operated. A 204-foot AB-216 radio antenna tower enabled him to receive radioed instructions from the division commander and to pass on instructions to the Army element of the Mobile Riverine Force and other units operating in the region. Swamps and heavy jungle of the delta region forced the tactical units to rely on small craft as primary transportation for conducting operations. It was the 2d Brigade's responsibility to patrol waterways, searching out and destroying the enemy.

The brigade soon learned that transportation was not its only problem. Because of the relatively flat terrain and a large operational area that was predominately swamp and heavy foliage, line of site communications were difficult at best. Few areas existed


ROTATABLE ANTENNA. 9th Signal Battalion, 9th Infantry Division.

ROTATABLE ANTENNA. 9th Signal Battalion, 9th Infantry Division.

in the delta which could support radio relay and retransmission stations. The joint riverine operations were relatively new, so there was no communications experience from which to draw. Communications facilities seemed plagued from the outset, and innovation became the order of the day.

The USS Benewah, which was outfitted in the Philadelphia Navy Yard, was the home of the brigade and the flagship of the flotilla. It was far from ideal for communications. Space was limited, and the compartment set aside for housing the brigade communications equipment was

too small. Only one twelve-channel VHF system (TRC-24, TCC-7, TCC-20) could be installed; it linked the brigade Headquarters aboard the Benewah to the division headquarters ashore. When the VHF system failed, FM and HF radio provided the only communications to the division.

There were also problems with installing antennas. The majority of the antennas were installed on the restricted space of the ship's superstructure. The closeness created frequency interference and in some instances complete blockage of radio communications. Operators of the VHF system found that antenna problems were further compounded by the ship's drifting at anchor, which disoriented the highly directional TRC-24 antenna. The 9th Signal Battalion obtained two UHF omni-directional antennas that were normally used with the VRC-24 air-ground radio. Mounting and coupling one omni-antenna to the TRC-24 receiver antenna and one to the transmit antenna kept signals from fading, and communications were possible regardless of the ship's position.

As the 9th Division refined its operations, a 200-foot AB-216 communications tower made tracking the Benewah easier, but the procedure was still cumbersome and tricky. It required two men to climb atop the tower, located at the 9th Infantry Division base camp, and rotate the AN/TRC-24 antenna in accordance with instruction received from an operator inside the VHF shelter on the


ground. The ground operator watched his receive-strength level meter and directed movement of the antenna to get a maximum signal level reading. This procedure was extremely dangerous because of the high frequency voltage on the transmitting antenna and the antenna height. During the monsoon season the problem of tracking the Benewah was further compounded by high winds and rain, which increased the possibility of serious injury to the men on the tower. To solve this problem, a rotatable antenna was constructed from scrap antenna mast sections, and a heavy-duty antenna rotor was obtained from the division Military Affiliate Radio System (MARS) facility. The rotor was controlled from the ground with an antenna control box. Two lengths of spiral-four cable provided the necessary rotor power. Initially a step-up transformer was used to compensate for the high line loss incurred through the use of the spiral-four cable. Experimentation showed that cable of less than two hundred fifty feet could be used with the rotor without too much voltage loss. Extensive modification eventually produced a basic antenna mount and fastener arrangement which was stable and simple to erect. The 9th Signal Battalion constructed and installed two such rotatable antennas.

Space was limited in the tactical operations center. An SB-22 switchboard cut down on the number of instruments needed; and FM radios serving the center were remoted through a patch panel to give the subscriber in the center access to multiple nets from his one remote station.

Multi-channel communications between the battalions and the brigade were provided by smaller, lighter equipment. The GRC-10 radio and TCC-3 multiplex equipment provided four voice channels between the Benewah and the battalions. These VHF transmissions, as well as the TRC-24 transmission to division, terminated on the brigade switchboard.

The Navy normally hard-wires all its communications equipment, so reconfiguring circuits is difficult. For the brigade, with its ever changing communications requirement, this system just would not suffice. On the request of the brigade signal officer, the Benewah was refitted so that the operator could patch equipment temporarily where it stood. This arrangement saved time by allowing the operator to bypass faulty equipment and patch inoperable equipment as needed; communications circuits could be rerouted quickly aboard ship.

Original plans for telephone switching called for a twelve-line capacity SB-22 switchboard, which proved to be unsatisfactory. Even after the installation of a stacked (additional jack field sec-


tion) sixty-line SB-86 switchboard it was not uncommon to find all cords in use during peak traffic hours. The SB-86 provided switching for all radiotelephone circuits as well as internal telephones aboard the ship. Messengers who delivered correspondence aboard ship by foot and between ships of the flotilla by launch reduced switchboard traffic.

Infantry maneuver elements of the brigade relied extensively on FM and HF single sideband radios. Those conducting land operations used the manpack PRC-25 radios; those aboard barracks ships, attack boats, command and control boats, and monitors normally used the AN /GRC-106 and the VRC-12 series. FM communications were provided to the widely dispersed maneuver elements operating beyond normal radio range by V RC-49 retransmission units installed aboard command and control boats and by airborne relays. Radios installed in command and control helicopters allowed the brigade and battalion commanders to take advantage of altitude for increased line of site communications.

Communications maintenance facilities for the brigade were also afloat; an electronics maintenance team from the division maintenance team from the division maintenance battalion was located aboard the USS Askari to repair equipment there when needed.

It was not common practice within the division to establish a division alternate. The extra equipment was used to install a second multi-channel system between division main and the brigades (excepting the 2d Brigade, located aboard the Benewah) as a hedge against enemy attack or other unforeseen troubles.

Division standing operating procedures called for four sole user circuits to brigade-three voice circuits, one from the division G-2 to the brigade S-2, one from the division G-3 to the brigade S-3, and one from the division artillery element in the tactical operations center to each artillery battalion; the fourth circuit was from the division communications center to the brigade communications center by teletypewriter. These circuits were split between the two parallel multi-channel systems, so spare channels were available should one system fail. Circuits could be rerouted at the patch panels within one or two minutes. Since only the 9th and elements of the 1st Signal Brigade were using the TRC-24 vans in this area, U.S. Army, Vietnam, allowed the division signal officer to coordinate multi-channel frequencies. Interference was as a result practically nonexistent.

The division also placed great command emphasis on using systems control and technical control to ensure greater reliability.





SB-22 SWITCHBOARD aboard the Benewah.

SB-22 SWITCHBOARD aboard the Benewah.


One technique was to tie channel 12 of the TRC-24 systems into an SB-22 switchboard at systems control for circuits terminating at division headquarters and at technical control for those, terminating at the forward area signal centers.

As the division gained more experience in riverine operations, the 2d Battalion commander found that a single command post aboard the Benewah would not suffice. He established a forward command post with the command post of the 3d Battalion, 34th Artillery, his direct support unit, aboard a medium landing craft.

The only normal communications with that artillery battalion floating command post were FM; telephone communications to the brigade forward command post were badly needed. The signal battalion obtained a medium landing craft, installed a VHF terminal aboard it, and tracked the boat from the Benewah as it moved along the rivers and canals with the brigade forward command post landing craft. The forward command post was activated only when the landing craft was beached or anchored, and telephone communications were required only at those times. The VHF radio system, however, was maintained at all times; anchoring or beaching the multi-channel boat alongside the brigade command post boat, passing a twenty-six pair cable across, and hooking the telephones was a simple procedure.

As the enemy modified tactics to counter the success of the riverine operations of the 9th Division, the division also modified tactics by placing one battalion ashore to conduct airmobile operations in coordination with the riverine operations being carried out by the remainder of the Riverine Brigade. Fire Support Base TIGER II, approximately seven kilometers south of Ben Tre, was the location of the shore battalion headquarters and one company. The other companies were located in small fire support bases five, or six kilometers from Ben Tre, which was in the heart of the enemy infiltration area. A four-channel VHF system provided communications between battalion headquarters at Fire Support Base TIGER II and the brigade at Ben Tre. The battalion communicated with the companies in the small fire support bases by wire. Experience had shown that despite doctrine, wire could not be used because the Viet Cong would cut it as soon as it was put in. In this case, however, but for one exception the spiral-four cable proved effective even though there were larger numbers of the enemy operating in the area.

The geography of the delta region posed some special problems for the communicators of the 9th Division. One of these was grounding. multi-channel and telephone equipment routinely


produced noisy communications twice a day, at low tide. During high tide the water table was one foot below ground level; at low tide, thirteen feet. Of various methods attempted to solve the problem, one success was welding a large quantity of scrap metal together and burying it below water level at low tide. A long ground rod welded to the scrap metal and extended to above ground level provided a connecting point.

A special problem for photographers was the absence of virtually any clean water. Water provided by engineer manned water points and later the base water system left spots on film and prints from sediment. Filters used by the engineer water points were in short supply and could not be spared for photographic usage. A paper filter, found in use at the helicopter rearm and refuel points initially proved unsuccessful, but water run through the filter in the reverse direction from that specified for fuel came out clean and clear. A filter assembly was installed at the photo lab, and a new problem developed-everyone came there to get good drinking Water.

At no place in Vietnam was the need for towers to gain antenna elevation and extend range more critical than the delta. The extremely flat terrain afforded no natural elevation where FM and VHF radio antennas could be installed to increase their range. Towers were the solution, but steel towers were in short supply. Eventually U.S. Army, Vietnam, located a few 300-foot towers installed at navigational aid sites. These were offered to the 9th Division for the dismantling and transportation. Two towers were dismantled and moved to division headquarters with the assistance of a Navy large landing craft to transport heavy items. The basic plan was to install 78-foot towers at selected battalion base camps to raise FM and VHF radio antennas. Battalion commanders resisted; they felt that the required red aircraft warning light would provide a perfect aiming stake for enemy mortar-men. After considerable persuasion, one battalion commander agreed to let the signal battalion build a tower at his base camp. He broke the ice, and the towers cropped up at other locations throughout the division to give the communicators a much needed boost in getting some of their very demanding VHF links.

Cambodian Incursion

As American withdrawal continued through 1969 and early 1970 the enemy buildup of supplies just across the Cambodian border posed a distinct threat to U.S. forces and to Saigon. This


threat coupled with governmental upheaval in Cambodia prompted the U.S. incursion into that country.

The 1st Air Cavalry Division's Operation SHOEMAKER was the ultimate test of the division's ability to communicate. On 24 April 1970, the division was instructed by II Field Force headquarters to begin planning for a possible combined U.S.-Vietnamese operation into the "Fishhook," that section of Cambodia which juts between War Zone C and Binh Long Province of South Vietnam. The division was ordered to be ready to move within seventy-two hours with the mission of neutralizing the Central Office of South Vietnam (COSVN), the Communist high command for all activity in the South Vietnam base area. The task force was under the command of Brigadier General Robert Shoemaker, the assistant division commander for maneuver. General Shoemaker elected to locate his task force headquarters with the 3d Brigade at Quon Loi to reduce the personnel and equipment support requirement. The plan was simple in concept but difficult in execution. The rapid growth of the task force outstripped the communicator's ability to respond. Initially the force consisted of the 3d Brigade, 1st Cavalry Division; the 3d Airborne Brigade of the Army of the Republic of Vietnam; and the 11th Armored Cavalry Regiment plus normal support including artillery and one assault helicopter company. This organization was reinforced on 30 April by one mechanized infantry battalion from the 9th Infantry Division; one tank battalion from the 25th Infantry Division; one battalion (the 5th Battalion, 12th, Infantry) from the 199th Light Infantry Brigade; and two battalions from the 2d Brigade, 1st Cavalry Division.

On 1 May Operation SHOEMAKER began. The 3d Brigade struck north across the border. To the east, in the deep finger of the Fishhook, the 11th Armored Cavalry Regiment advanced to the northwest into the objective area while simultaneously three battalions of the Vietnamese 3d Airborne Brigade were combat assaulting by helicopter into three objectives north of the Central Office. Subsequently they were to move south, in a large pincer movement, to cut off enemy routes of escape.

Communications at Quon Loi became more and more difficult as the burgeoning task force deployed. Frequency modulated radio was a major problem because of the size and diversity of the force but was still the primary means of communication for every major and minor unit in the operation. Interference was commonplace up and down the frequency spectrum as a result in part of the secrecy required by the operation and in part the commonality and overlap of frequencies used throughout the III Corps zone. Dupli-


cation of frequency assignment mushroomed further as units from other divisions and separate brigades joined the task force. The congestion of radios and associated antennas at Quon Loi was extreme, with at least a hundred FM radio nets in the immediate area of the joint task force headquarters and many (if not most) antennas using the same AB-216 tower. At one time nine VHF, one UHF, seven log periodic, and thirty-six 292 antennas could be counted .on one tower belonging to the 3d Brigade. This number was in addition to antennas mounted on the towers of the 11th Armored Cavalry Regiment and 595th Signal Company (36th Signal Battalion) which were located less than three quarters of a mile away. The signalmen solved the FM problems by adjusting the receiver transmitters for peak power output, utilizing airborne and ground relays on Nui Ba Den and Nui Ba Ra, switching frequencies, reconfiguring antennas, and checking and rechecking the avionics equipment.

Very high frequency radio relay was initially installed between Quon Loi and Camp Gorvad (Phuoc Vinh) by a four-channel AN/ GRC-163 system. After D-day multi-channel communications were increased by additional channels provided by the II Field Force and 36th Signal Battalion (Area) communication systems. The communications support concept of Operation SHOEMAKER called for telephone service off the 3d Brigade's SB-86 switchboard. With the rapid buildup of communications this board was soon saturated even though it had been expanded to ninety lines.. By the third day of operations the signalmen were forced to establish a separate switchboard geared to the requirements of the task force using personnel from the 13th Signal Battalion. Lieutenant Colonel Norman E. Archibald said, "To put it bluntly-it was a hand to mouth operation. We always kept our fingers crossed hoping that nothing would happen to the division wire system while we diverted personnel and material assets to the nodal head at Quon Loi. "

Coordinating and controlling the signal activities of all the units involved in SHOEMAKER was a difficult task for the signal staff. They were hindered, albeit unintentionally, by the secrecy which surrounded the operation. For example, coordinating the signal operation instructions, cipher key-lists, operation code material, and frequencies with elements of the 9th Infantry Division, 25th Infantry Division, and 199th Light Infantry Brigade was a real nightmare.

The rapid growth in the number of units assigned to Operation SHOEMAKER also complicated coordination and control. As each


of the units was assigned to the task force, it became increasingly difficult to meet individual communication needs. This problem was evidenced by the increase of cable and wire systems, installation of additional VHF circuits, and abundance of RC-292 antennas with their requirement for frequencies from the already crowded spectrum. By the fifth day, the task force had increased to a size equivalent to nearly two divisions. At this point, command and control reverted back to the division at Phuoc Vinh and the operation was reoriented toward the northeast, north and northwest of the Cambodian border.

The 1st Cavalry Division continued to shift its forces, and on 13 May the 3d Brigade moved from the Fishhook in an air assault northwest of Bu Dop. The void left in the western portion of the Fishhook was filled by the U.S. 25th Infantry Division, while the Vietnamese Airborne Division had its own area of operation in the southern Fishhook. The 1st Brigade and the 1 lth Armored Cavalry Regiment remained in the northern Fishhook adjacent to the "Flatiron," but a final realignment on 19-20 May placed the lst Brigade with two battalions in Cambodia near the town of O Rang, north of Bu Gia Map. The first team now had eleven battalions, three armored cavalry squadrons, and the 1st Brigade Tactical Command Post, located at Fire Support Base DAVID in Cambodia.

The tactical implications of O Rang were interesting primarily because of the uncertainties involved. The division did not know if the enemy force was still in the vicinity and was not completely sure if communications could be established between O Rang and the division because of the distance (140 kilometers), the mountainous terrain, and the lack of previous reconnaissance. On 20 May 1970, the 1st Brigade air assaulted into O Rang, and personnel from the 13th Signal Battalion were among the first to touch the ground. Their equipment included an AN/GRC-163 four-channel radio, two 1.5-kilowatt generators, and several batteries. The communications issue remained in doubt until approximately four hours after touchdown. Fire Support Base DAVID was at the 3,000-foot level; this elevation plus the angle of elevation from O Rang to Nui Ba Ra (where the VHF channels were rerouted to Phuoc Vinh) was sufficient to overcome any terrain obstacles, and the system was brought in.

The 13th Signal Battalion continued to provide backup to the lst Brigade communications platoon while it was in Cambodia. Early in the morning of 14 June the North Vietnamese assaulted Fire Support Base DAVID from three sides. The attackers were driven off after a bitter fight. The brigade signal officer and several


other communicators were severely injured, and considerable equipment was destroyed. Acting Sergeant Goldsworthy, who was in charge of the VHF element, not only maintained communications throughout the firefight but earned the Silver Star for gallantry in action.

Lieutenant Colonel William R. Rogers, the division signal officer for the 25th Infantry Division and commander of the 125th Signal Battalion, noted that planning was so tightly held that the commanders, including the signal officer, did not know what was really happening until it happened and that the division did not move its headquarters closer to the area of operation, so the signal officer had to hold communications assets, vitally needed in other sectors, in reserve for a possible forward displacement that never materialized. These problems highlighted two recurring frustrations of the division signal officer throughout the conflict in Vietnam.



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