Communications Security Threat

Few communications subjects can arouse more controversy among professional soldiers than that of security. The argument centers on security versus responsiveness. The points under debate usually involve the techniques used to try to gain some degree of communications security, such as changing call signs and frequencies and using codes for the coordinates of locations and other critical data. To many people, the ideal solution to all but the frequency problem would probably be a small, lightweight, durable, unclassified black box which would automatically scramble and unscramble transmissions so that only those people with a similar black box could understand the transmission. The black box was not available when U.S. troops were committed in Vietnam.

The security measure of changing call signs was very controversial on two points. One was the confusion created by changes. Colonel Sid Berry, the commander of the lst Brigade, lst Infantry Division, from June 1966 to February 1967, spoke for many commanders when he said, "It simplifies communications for units and individuals to keep the same frequencies and particularly call signs. Frequent changing of call signs confuses friends more effectively than enemies." The other point was that new call signs frequently cast a poor image or were too long. Although there were many complaints about the denigrating image reflected by call signs, one of the most vivid was provided by Lieutenant Colonel Norman E. Archibald when he recalled his 1970 experiences as division signal officer of the 1st Cavalry Division: "The signal battalion still had a difficult time selling call signs like 'Supreme Capon' ( . . . the commander said, `What? You want everyone to call my troops castrated chickens?') . . ." Brigadier General William S. Coleman, in 1967-68 assistant commander of the 1st Infantry Division, expressed both objections: "Another change that I hated to see was the fancy call signs that the division was ordered to adopt. Imagine being on the radio and saying, 'Sailing Gerta Delta One One Juliet, this is Mister Taboo Four Four.' Why, by the time


you get the call signs out, you've forgotten what you wanted to say."

Although these and other complaints were understandable, a communications security problem did exist in Vietnam and had to be dealt with. Early in the war, many people apparently had assumed that the enemy was unsophisticated and that communications security did not warrant much concern. That may have been true when American troops first arrived, but the enemy quickly adjusted.

It soon became evident that he was using poor communications security to good advantage: U.S. troops found their own radio equipment when they swept enemy positions; the enemy might disappear from a location just before a planned U.S. attack; B-52 bomber strikes did not produce expected results because the enemy apparently anticipated them. Some plans probably leaked to enemy agents operating within the Vietnamese political structure at the province and district levels, where Americans had to get political clearance for operational areas to ensure that there was no conflict with local defense forces. But even these suspected leaks could not explain the problems in established free fire zones and already authorized areas of temporary operations. There had to be another source from which the enemy was obtaining critical information.

There was. On 20 December 1969 elements of the 2d Battalion, 2d Infantry, and of the 2d Battalion, 28th Infantry, both from the 1st Brigade, 1st Infantry Division, overran an enemy installation about four kilometers north of Ben Suc in the II Corps zone and captured twelve enemy soldiers. They also seized an assortment of documents and communications equipment, including three U.S. Army FM radios of the AN/PRC-25/77 variety; one Chinese Communist AM receiver, compatible with the U.S. AM radios of the AN/GRC series; seven Sony transistor radios; one Panasonic receiver; one homemade receiver; and one homemade transmitter. All the equipment was in excellent operating condition, and the homemade receiver and transmitter reflected a very high quality of workmanship. With this equipment, this Viet Cong and North Vietnamese Army radio intercept unit could monitor and exploit virtually all nonsecure voice and manual Morse code communications among U.S. and allied tactical units within receiving range. Interrogated prisoners indicated that, along with building up equipment, the enemy had instituted a large number of English linguists. These linguists became an integral part of many Viet Cong and North Vietnamese units such as the intercept unit.


Among the captured documents were several booklets containing extensive instructions on proper intercept techniques and detailed analyses of the communications procedures and exploitable weaknesses of U.S. and allied units. Specific comments were included on the communications procedures of the 1st Infantry Division, 1st Cavalry Division, 4th Infantry Division, 25th Infantry Division, 11th Armored Cavalry Regiment, 5th Vietnamese Division, and the various Military Assistance Command advisory teams. These booklets were current, lengthy, and very detailed. On point of origin codes the instruction was, ". . . they usually use landmarks or a PO (point of origin) from which they use LEFT, RIGHT, UP and DOWN to designate a position." In one journal entry a 1st Infantry Division unit message had been copied: "Presently my one six element is at CPT Coutine (actually Checkpoint Canteen) R.6 U 2.2." The actual coordinates were written above the entry. That decoding points of origin and shackle codes appeared frequently throughout the journal indicated that deciphering such codes apparently posed no major problem.

The unit also noted the importance of obtaining information from warning nets. By monitoring these nets the enemy could get data on artillery and air attacks, and transport of wounded. He could extract all intelligence concerning the units engaged, fire bases, landing zones, and air reconnaissance. He could also get information that would help analyze the traffic intercepted from U.S. infantry communications. The journal identified U.S. advisory and South Vietnamese unit nets as very productive for intelligence data. It further noted that the South Vietnamese made monitoring easy because they never changed call signs or encrypted messages. The journal gave examples of B-52 warning messages. It instructed the monitors to be sure to get the coordinates because they represented the box, or target area, which had to be reported for the security of their own troops.

The captured radio intercept unit was one small team targeted on several American and Republic of Vietnamese units. A logical assumption is that by 1969, when this unit was captured, the enemy could field a number of such teams. This attribute of the enemy in Vietnam must be accorded any future enemy; that is, his ability to adjust to American operational techniques and to improve his capacities. The enemy in 1969 was not what he had been. As the situation changed, he changed.

These examples are but a few of how the enemy used U.S. communications means and procedures to gather intelligence and to assist his operations. There are numerous instances on record of the


enemy jamming radio frequencies and sending false messages. These bogus transmissions used imitation to try to turn fires or forces to an area chosen by the enemy. In one case the enemy tapped the internal telephone lines of a defensive base and diverted reserve forces from the area where he attacked.

General Abrams, then head of the Military Assistance Command, after examining the captured documents and being briefed on the radio intercept team incident, summed up his reaction

"This work is really rather startling; the attention to detail, complete accuracy, and thorough professionalism is amazing. These guys are reading our mail, and everyone will be informed that they are."



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