Special Communications Operations and Innovations

Mobile Riverine Force: An Unusual Test

In June 1967 General Westmoreland created a new, completely integrated command composed of a U.S. Army infantry brigade and a U.S. Navy task force: This Mobile Riverine Force was amphibious, operating entirely afloat; it was reminiscent of river forces used by the United States in the Civil War when the Union Army operated on the Mississippi, Cumberland, and other rivers. The force was complete, independent of fixed support bases, and with all of its normal fire support embarked or in tow. The great flexibility of the Mobile Riverine Force increased our ability to take the fight to the Viet Gong in previously inaccessible areas. The battleground was the mighty Mekong River and its delta.

The Mekong Delta is drained principally by four channels of the Mekong River as it flows southeastward from Cambodia to the sea. Some 1,000 miles of primary canals crisscross the area, and in between the canals lie thousands of square miles of rich rice lands. Few roads penetrate the delta. Towns and villages sit on the mud banks of canals and rivers, surrounded by rice paddies. Little of the land is more than ten feet above sea level. Although the Mekong Delta is among the world's richest lands for rice-growing, it is formidable ground for the infantry soldier on foot and his modern, but often heavy, supporting equipment.

The assault unit of the Mobile Riverine Force was the 2d Brigade of the U.S. Army's 9th Infantry Division, a brigade specially tailored for combat on the rivers and canals. Since the riverine battalions operated from ships and assault craft, the infantrymen's traditional jeeps and trucks were not used. Instead, a small flotilla of boats powered by outboard motors was made available for transportation. The supporting artillery was streamlined for operation aboard towed barges instead of in fixed fire support bases. The organic communications resources of the riverine brigade were essen-


tially the same used by other infantry except that man-packed, portable voice radios were substituted for those radios mounted on jeeps and trucks.

The U.S. Navy complement of the Mobile Riverine Force manned a fleet of assault troop carriers, fire support ships called monitors, command and communications boats, repair and supply ships, medical craft, a barracks barge, and two self-propelled barracks ships. These naval craft were specially prepared and outfitted in the United States for deployment on the waters of the delta. They were rigged with extra guns and cannon and were heavily armor-plated to ward off the inevitable Viet Cong rocket-propelled grenades and heavy-caliber machine gun rounds.

The command and communications boat was, as the name suggests, a floating command post, providing radio communications for both the Army troop commander and the Navy boat commander. One of these craft was usually available for each battalion-size element in an operation. This communications boat itself took on the appearance of a floating antenna field, since nine combat voice radios were installed below the deck and the topside bristled with nine antennas. With this equipment the troop commander maintained radio contact with his assault troops, the supporting artillery located nearby on barges, the ever-present helicopter gunships circling overhead, the monitors-fire support boats-the tactical fighter bombers of the Air Force, the South Vietnamese Army counterpart commander, higher headquarters, and the medical evacuation helicopters.

Much of the credit for maintaining such extensive communications must go to the communicators of the Mobile Riverine Force, both Army and Navy, who eliminated the interference inherent in having so many radios transmitting and receiving from a floating metal platform. The successful operation of radio circuits from the command and communications boats can be attributed to excellent frequency control, many on-the-spot innovations, and a degree of divine providence.

The USS Benewah, one of the self-propelled barracks ships, was the command post of the entire Mobile Riverine Force and was the rear headquarters of the 9th Infantry Division's 2d Brigade, the Army complement. It was the job of the 9th Signal Battalion, the organic communications unit of the division, to provide and operate telephone and message communications between the USS Benewah and division headquarters. Methods were quickly devised to track, by means of radio, the USS Benewah while it sailed on the delta's canals and streams; by use of multichannel radio relay


Photograph: USS Benewah, A Riverine Force Command Control Flagship


equipment, the essential telephone and message communications were maintained. Whenever the ship approached the maximum range limit of the radio equipment, relay stations were activated in strategic locations to span the miles and maintain solid communications. Initially, the directional antennas both at the ground stations and aboard the USS Benewah were kept properly aimed, as the ship sailed or swung at anchor, by signalmen turning the antennas slowly by hand until the strongest signal was indicated on the receivers. This effective but primitive system was soon replaced with special antenna-rotating motors rushed from the United States. The rotating motors were similar in design and were operated on the same principle as the "rotors" which many families have for their home TV antennas.

In June 1968 the 9th Signal Battalion was faced with the problem of establishing telephone and message communications for another floating command post besides that on the USS Benewah. This forward command post of the Mobile Riverine Force was operating from a medium landing craft only 73 feet long and 21 feet wide. Since the boat was far too small to accommodate the radios and power generators as well as the men of the forward command post, a second landing craft was found on which the 9th Signal Battalion troopers installed multichannel radio relay equipment and power generators.

The effectiveness of this system of communications can best be illustrated by describing a deployment of the Mobile Riverine


Force in December 1968. A multichannel radio link was installed from the 9th Infantry Division main command post at Dong Tam to the Mobile Riverine Force forward command post located in the My Tho River a few miles from Dong Tam. As this command post craft moved down the river in the early morning hours, destined for Vung Tau and its ultimate site in Long An Province, the USS Benewah also weighed anchor and sailed for Vung Tau. As each ship entered the South China Sea, the 9th Signal Battalion relay station at Vung Tau picked up each radio link and relayed it back to Dong Tam. The signalmen at Vung Tau were constantly rotating antennas for maximum signal strength, as were the signalmen aboard the USS Benewah and the forward command post vessel.

At Vung Tau the USS Benewah anchored, but the landing craft containing the forward command post and the waterborne radio relay equipment moved up various twisting canals and waterways to a position forty-five miles northwest of Vung Tau. This movement took several days. Each night the two landing craft beached and established a base from which supporting artillery fire was provided and controlled through the telephone circuits passing over the radio relay link. While the boats were moving, the Mobile Riverine Force forward command post, of course, had no access to these telephone circuits. But as soon as the boats either beached or anchored, the 2d Brigade's commander and his staff on the landing craft were provided with the telephone and message communications via field wire strung between the two vessels. Because of this increase in communications support, the Army and Navy commanders of the Mobile Riverine Force now had the capability to operate at distances far from their rear or permanent headquarters and still influence and control the over-all operation of the force.

The Mobile Riverine Force was a highly successful U.S. combat unit throughout its period of operation. The innovations of the 9th Infantry Division signalmen tied this potent amphibious force together by means of solid communications, while the force elements freely operated in waterways that were previously controlled, for the most part, by the Viet Cong.

Battlefield Secure Voice Equipment

One of the most significant and vital communications innovations during the Vietnam War was the development of equipment capable of providing complete security to the combat voice radio nets of the fighting units. From the early days of the war the sen-


for commanders could discuss classified matters over fixed secure long-distance telephone systems such as "Talk Quick" and ultimately over the worldwide, sophisticated Automatic Secure Voice Communications System. But the division commander and his battalion commanders did not have the means of discussing classified operations with their combat units unless a message was written, encoded, and transmitted over either the voice radio net or the message circuits. The procedure was extremely slow and therefore suffered from the all too common practice of not being followed at all. The hope that "maybe the enemy is not listening this time" was much too prevalent in the U.S. forces. This false sense of security did not appear for the first time in the Vietnam War; it was equally common during World War 11 and the Korean War.

The Communists in Vietnam had always capitalized on their ability to mount a surprise attack with rockets or mortars or to plan an ambush with mines and machine gun fire. During 1968 there was growing evidence that the enemy was placing greater emphasis on exploiting our communications through interception and communications deception. As far back as the 1967 battle for Dak To, Viet Cong radios eavesdropped on U.S. radio transmissions. When fighter bombers asked the U.S. infantry to place yellow smoke in front of the most forward friendly positions, enemy mortars dropped yellow smoke on our troops, hoping to mislead the Air Force into bombing friendly forces.

During an operation in January 1968 near the Cambodian border, units of the U.S. Army's 25th Infantry Division were startled to hear a radio operator claiming to be the leader of an Australian patrol just ahead of them. The American commander, whose radio call sign was MANCHU SIX, was skeptical. His patrol started a search. As the U.S. troops were moving through the jungle, the unknown radio operator called "MANCHU SIX, MANCHU SIX, this is ALFA BRAVO 13, over." When the infantry commander replied, the alleged Australian station transmitted, ". . . the Viet Cong in my area are moving up on your southern flank, repeat, southern flank, over." When his troops deployed on the southern flank began to receive small arms fire, the U.S. battalion commander asked for an identification. The reply was "We are an Australian 173d Airborne unit and we were dropped here this morning at 0600 hours, approximately 23 meters north. We are on a search and destroy mission. Over." A careful check with the command operations centers of both the 25th Infantry Division and 11 Field Force revealed that the Australian forces did not have a unit with a "173" designation and that, further, there were no Austra-


lian forces operating in the immediate area at that time. The next radio transmission heard was "BRAVO BRAVO 15, this is ALFA BRAVO 13. The American unit just east of you, repeat, just east of you, thinks you're Victor Charlie [Viet Cong]. Do you read? Over." At that point the U.S. Battalion commander got on his radio and advised the unknown stations that they should "stay on the ground and not move. If you do not move around, everything will be okay. If, in fact, you are phony and a VC station and continue to move to my location then I will consider you enemy forces and will engage. Do you roger? Over." The unknown station stated that it would stand off and not move until contacted by the U.S. infantrymen. But these allegedly friendly troops were never heard from again. A search of the area by U.S. Troops revealed no Australians at all; in fact, the only signs of prior occupancy were abandoned ambush positions of the Viet Cong that showed signs of hasty departure.

These instances emphasized the magnitude of the Viet Cong and North Vietnamese efforts to intercept Allied communications. The simplest and fastest method for intercept is, of course, to use captured communications equipment. By mid-1968, the Viet Cong and North Vietnamese had in their possession many American-made radios which they had captured, primarily the portable radios used by U.S. Infantry soldiers.

However, the efforts of the Viet Cong and North Vietnamese to monitor U.S. Radio transmissions in order to use the information against us were increasingly frustrated as secure voice equipment became available. The first such equipment received in Vietnam was developed for use with combat voice radios mounted on vehicles, and for sets placed in tactical operations centers and similar locations. This configuration, received in 1966, allowed the radio operators who worked from essentially fixed locations, such as division and brigade headquarters, to discuss classified information freely because the enemy simply could not understand them.

The next breakthrough was the introduction in Vietnam during 1968 of smaller, man-carried, secure voice equipment which allowed patrols and small units operating in the jungles to secure their radio nets. That same year a model specially configured for installation in aircraft, both helicopters and conventional fixed­wing airplanes, was sent to Vietnam. The stage was now set for most of the U.S. mobile combat radio stations to operate in the secure voice mode.

Initially, however, the new equipment was not generally used. There were three reasons for this delay. First, certain special cables


and unique items were slow in being sent from the United States. Second, there were misconceptions about the security requirements, the integrity of the system, and the operational value of the equipment. Third and probably most important, a secure retransmit capability was not available; radios using the secure equipment could not automatically relay transmissions. The first two problems were handled quickly. Emphatic messages were rushed to the United States and got the needed auxiliary equipment moving on the way. Instruction from senior officers and teams of Signal Corps communicators demonstrating the equipment helped the combat soldiers to realize its value. But the third problem, the lack of retransmission capability, had to wait until 1969 for solution simply because the equipment did not yet exist. Once research and development and the wheels of industry were running at high speed, the secure voice repeaters were quickly obtained and put to efficient use in Vietnam. Thus, in the latter part of the war, these secure voice devices were extensively used-a big step toward the ulimate goal of completely securing the Army's combat communications.

Airborne Radio Relay

The success which the skytroopers of the 1st Cavalry Division had with airborne radio relay in the famous Ia Drang valley campaign in 1965 paved the way for extending a commander's ability to control the action on the battlefield. As the action of the war turned toward the remote valleys and plateaus bordering Laos and Cambodia, the cost-in terms of committed troops, expected casualties, and airlifts-of seizing and holding high ground for radio relay installation appeared to be excessive, if not prohibitive. Recalling the previous success of the 1st Cavalry Division, communications-electronics planners of the U.S. Army, Vietnam, opted for an airborne radio relay system that would connect the field commander's combat voice radios with his higher headquarters. The call went out to the Department of the Army, and in early 1968 four relay aircraft were equipped and sent to Vietnam. They were successfully tested in combat in February and soon were flying relay missions throughout the country. The airborne relays were particularly valuable in support of the 1st Cavalry Division's relief of Khe Sanh in the northern part of the I Corps Tactical Zone in the spring of 1968.

Although these airborne relays extended the field commander's span of control and often provided the only means of communicating with ground troops in contact with the enemy, there were major limitations to the system. These limitations primarily involved


the aircraft itself. The twin-engine Caribou airplane that the 1st Cavalry Division employed so successfully in 1965 had subsequently been taken from the Army's inventory and turned over to the Air Force. As a result, the airborne radio relay system was installed in the Army's single-engine Otter airplane. These older Otters were difficult to maintain. The radios installed were not capable of se­cure voice retransmission and were actually too heavy for the underpowered Otter.

Once again, therefore, the Department of the Army was asked for help. U.S. Army, Vietnam, asked that the Otter be replaced with a more powerful, all-weather aircraft and that the present radios be replaced with newer, lighter models designed especially for aircraft. The result of this request was that the 1st Signal Brigade received nine twin-engine U-21, or "Ute," aircraft in the fall of 1969. Each was equipped with a radio console capable of relaying three voice radio nets. But the most significant fact was that all three nets could now operate and be relayed in the secure voice mode. The first missions involving this new relay system proved that a secure voice radio link of 140 nautical miles could be readily established at an altitude of only 3,500 feet. Since the Army's U-21 plane can stay aloft on station for several hours at a much higher altitude, the occasions when a small unit or long-range patrol was without communications were virtually nonexistent.

Airborne radio relay, however, contributed to the problem of radio frequency interference. The frequency spectrum for the combat radios was very limited and had to be allocated among the many U.S. Army and other combat units deployed in Vietnam. In order to minimize the interference of the radio nets with each other, judicious planning was necessary to assure that those units which had to share a common frequency were sufficiently separated. All of this careful planning was for naught, however, when an airborne relay station was capable of transmitting over five or six times the distance of a station on the ground. Invariably, reports of frequency interference would start to arrive at a combat headquarters shortly after the relay aircraft arrived in its assigned orbit. The only feasible solution was for the U.S. Army, Vietnam, to reserve a certain number of frequencies for use in airborne radio relay operations alone. This expedient solved the interference problem but further decreased the number of radio frequencies available for general use. Therefore detailed frequency management was essential from the maneuver battalion to the highest levels in Vietnam.


Pictorial Operations

The face of war is ugly, but it is a face that must be recorded. Recording and photographing the war was one of the missions of the U.S. Army Signal Corps in Vietnam.

A young lieutenant deploys his infantrymen into an ambush position to the accompaniment of the soft whir of a motion picture camera. Farther north a medical evacuation mission flying through heavy enemy fire is recorded in a series of short clicks drowned out by the roar of the helicopter. In the Mekong Delta, a U.S. Army unit helps build homes in a small village as one man with a necklace of cameras surveys the scene through a light meter. Unconnected? No, not really. To the Signal Corps combat photographer it is just another day of recording both the war itself and the Army's reconstruction efforts throughout South Vietnam.

In 1962 the only operational U.S. pictorial unit in Vietnam was an element of the 39th Signal Battalion. Late in 1965 this element was transferred to the 69th Signal Battalion, where it merged with the 69th's organic Audio-Visual Platoon. The capabilities of the resulting organization were generally limited to black and white still photography on a very modest scale. The arriving U.S. Combat divisions and separate brigades had their own photographic sections, as did the signal battalions of the field forces, but their capability was also limited to a few combat photographers and black and white film production.

As the war increased in intensity, so did the clamor for photographic documentation. In order to place some control over the countrywide pictorial effort, the 1st Signal Brigade created the Southeast Asia Pictorial Agency late in 1966; however, this was only a staff or management type of agency, consisting of one or two officers. Not until almost a year later was there any significant improvement in photography and processing film.

In August 1967 the pictorial agency was redesignated the Southeast Asia Pictorial Center. Concurrently, men and equipment for photo support on a large scale began to arrive in Vietnam. This organization soon became the most extensive and complex photo facility the U.S. Army had ever placed in a combat zone. In addition to its central facilities at Long Binh, the pictorial center maintained and operated photo support units at Phu Bai, An Khe, Cam Ranh Bay, Can Tho, and Saigon. Each unit was capable of providing complete photographic service within its area of operation. The Southeast Asia Pictorial Center was the first Army photo facility to be capable of color processing and printing in a combat zone.


Photograph: Combat Photographer Of 221st Signal Company Gets A Helping From Vietnamese Civilian


The Southeast Asia Pictorial Center was operated by the 221st Signal Photographic Company. This unit, activated in June 1966 at Fort Monmouth, New Jersey, arrived in Vietnam in photographic team increments during 1967 and 1968 and has a short but colorful combat history. Its combat photographers as well as those of the organic signal units of the field forces, divisions, and bri-


Photograph: Communicator Places A Mars Call, Christmas 1969


gades, captured on film the realities of the Vietnam War. Courageously entering the combat area, armed with a roll of film and a camera, photographers sometimes lost their lives as they tried to capture the action of the combat men they accompanied. One of these photographers was Specialist David A. Russell of the 221st Signal Company, who was killed in action on 18 March 1969 while on a combat photo mission in South Vietnam. The 1st Signal Brigade dedicated a new Army message relay center at Long Binh on 25 October 1970 and named it the Russell Army Relay.

Military Affiliate Radio System

The Military Affiliate Radio System, or MARS as it is popularly known, is a worldwide network of military and designated civilian ham, or amateur, radio stations. Its mission is to provide emergency backup and supplemental radio links for U.S. Department of Defense communications. MARS operators perform vital


services for both the military and civilian population. Their services range from establishing rescue communications following an earthquake or tornado to allowing a combat soldier to talk via radio telephone to his wife.

The MARS operation in Vietnam is definitely small when compared with all other Army communication services provided, but to hundreds of thousands of servicemen in Vietnam and their families back home it has been the most important service provided by the Signal Corps. After receiving the approval of the government of the Republic of Vietnam, the Military Affiliate Radio System began operation in Vietnam in late 1965, with all U.S. armed services participating. The Army MARS program in Vietnam started with just six stations. A personal radio and telephone hookup, or "phone patch," service began in February 1966 when the Department of the Army authorized the Vietnam MARS stations to make contact with designated stations in the United States. A U.S. contact station would then place a collect telephone call to a designated home, and for five minutes a soldier in Vietnam, perhaps one just in from a jungle patrol, could talk to his folks, who were halfway around the world. True, the reception was not always good because of ionospheric storms and weather disturbances. But who cared when an amateur radio operator in the United States was relaying to a soldier on a remote fire base in Vietnam the message "yes, she loves you and yes, she will marry you, over."

The U.S. Army, Vietnam, portion of the MARS program was completed in October 1969 with a total of forty-seven MARS stations throughout the republic, operating in seven different nets. The number of contact stations in the United States had grown to over a hundred. In the spring of 1970 the number of phone patches, or completed connections, from Vietnam to the United States reached an all-time high, averaging over 42,000 each month. At the conclusion of the MARS expansion program in Vietnam, soldiers in every American unit had access to a local MARS station. The backbone of the MARS stations in Vietnam was a commercially purchased, "off-the-shelf," single sideband radio, which was capable of spanning great distances. It was not only the main­stay for the MARS stations, but also for several years was used constantly in Vietnam to meet combat requirements for a long-range radio.


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