In the history of strategic military operations, it has long been public knowledge that Allied operations in the Pacific during World War II were indebted to the breaking of the Japanese operational communications codes. More recently it has been revealed that the British were able to break the strategic communications code by which Hitler received information and issued directives to his senior commanders. High command levels should have and did get top priority in American attempts to safeguard communications against similar breaches. With the men at the tactical level not really wanting signal security gear, there was a relatively modest attempt in the U.S. Army to develop new equipment for that level until the need became more evident.
Signal security equals a combination of people, equipment, and systems. People participating in tactical operations have a natural dislike for signal security measures; they prefer to conduct business in the simplest, most direct manner possible. Early in Vietnam, possible in most cases meant whatever superiors would permit in the tactical situation involved. The people part of the equation did not improve until the chain of command became convinced of the need for strict communications discipline. The conviction grew in proportion to information about the threat, and interest and participation grew as equipment and systems improved. The signal security problem was never fully resolved during the Vietnam era despite many improvements and much hard work. It was, and still is, one of the most difficult problems facing tactical communicators.
Along with the need to communicate as rapidly and directly as possible during combat, another factor worked against effective communications security: a soldier in the thick of battle feels the need for friendly assurance. This assurance can come from talking-to anyone else who has a radio. When this happens, chances are that little thought is given to what information is actually being transmitted.
Before secure voice equipment was in general use, oral communications requiring any secrecy had to be painstakingly coded
and decoded manually. All too often coding was circumvented in favor of simplicity, speed, and assurance. The tactical communicator needed some type of voice encryption device.
In 1965, when he was the U.S. Army, Vietnam, signal officer, Colonel Kenneth Ring recalled that there were some eight hundred KY-8 security devices in a stateside depot. These devices had no mounting brackets or connecting cables because their application had not been settled. Colonel Ring requested, on behalf of U.S. Army, Vietnam, that a new equipment training team be sent to Vietnam to demonstrate the devices and discuss their tactical uses; the team arrived in August 1965. From this start, the security device applications and improvements progressed through some tortuous evolutions.
Voice security devices were issued to the field units in Vietnam beginning in 1965 with the KY-8 for stationary or vehicular use; the KY-8 was fully distributed by the third quarter of fiscal year 1968. The KY-28 was issued for use in aircraft beginning in 1967 and ending a year later. The KY-38, for manpack or mobile use, also was issued initially in 1967 and was fully distributed in 1968.
The voice security gear, like most newly developed equipment, had its problems. The main cause of failure was heat. The KY-8 had to be kept in well ventilated surroundings and away from direct sunlight. During a 1969 presidential visit, an overheated KY-8 temporarily stopped secure voice communications between II Field Force headquarters and Tan Son Nhut.
The 199th Light Infantry Brigade station at Xuan Loc, in the 11 Field Force commanding general's secure FM voice net, continually broke down. Many pieces of equipment were generating heat in a poorly ventilated bunker and causing the KY-8 to fail. When it was moved to a cooler location, the KY-8 operated normally. Commanders and communicators became aware that, for reliable communications, the security equipment had to operate in the coolest possible environment.
In at least one case the ingenuity of a well intentioned communicator backfired. First, he placed a filled Lyster (water) bag over the KY-8 to cool it, but the device still overheated. Next, he removed the cover of the KY-8 to increase ventilation. That improved the operation of the KY-8 but violated security by exposing the equipment to view and giving the enemy an opportunity to intercept intelligible signals.
In a successful innovation, the 125th Signal Battalion engineered and installed a secure land line to expedite spot reports be-
tween the 372d Radio Relay Company and the 25th Infantry Division G-2. The battalion, operating two KY-8's in essentially a back-to-back test mode, replaced the short back-to-back cable with spiral-four cable of the required length. This system worked with almost no trouble and with very high quality.
During September 1968, the PRC-77 and KY-38 combination was issued down to the infantry battalion level, providing for the first time secure voice communications to infantry companies and in the battalion command nets. At the company level plans and operations could be discussed rapidly, safely, and explicitly without fear of enemy detection. Field units used two methods to offset the weight disadvantage (over 50 pounds) of the PRC-77/KY-38 package. One was to use the equipment fully by having one man carry the PRC-77 radio and another the KY-38. The second was to move the field unit as normal, then have supporting aircraft fly in the equipment for use in static or night defensive positions.
In the fall of 1969, reports on NESTOR (code name given narrowband secure voice equipment) utilization were revealing. Many units under the operational control of the II Field Force were not using their KY-38's as much as desired. The PRC-77/KY-38 when carried by one man, as intended, was just too heavy. Other units reported that they needed VRC-12/KY-38 interconnecting cables. They wanted to use the smaller KY-38 in lieu of the KY-8. The KY8 was prone to overheat and ran on generated power. Power was limited at fire support bases, and the field troops thought it unwise to run the noisy generators at night. The KY-38, on the other hand, was battery powered. Acting on this feedback, Electronics Command Laboratories went into an emergency production of interconnecting cables for the VRC-12 and the KY-38 and by late 1969 had produced three hundred. A substitution of the KY-38 for the KY-8 in vehicles was also agreed upon.
One of the most serious equipment problems in the field was the lack of kits and special cables for installing NESTOR gear in aircraft and vehicles. The installation kits and most of the cables was a supply responsibility of the Electronics Command. There was a variety of kits which adapted NESTOR equipment to the tactical series radios used in vehicles and aircraft. The initial supply of kits, once they had been developed, was adequate early in fiscal year 1969. As the use and uses of the equipment increased, however, kits and cable components became increasingly hard to find. The so-called X-mode cable for the KY-8 was also in short supply. Another aspect of the kit shortage came to light during the U.S. withdrawal from Vietnam. Although retrieving the NESTOR
equipment from vehicles was no problem redistributing it was often haphazard. A similar situation existed with KY-28's in aircraft, principally helicopters. Losses and evacuations of aircraft which had been fitted for the equipment made the shortage worse, since most of the replacement aircraft did not come with the kits installed.
The number of KY-28 keying devices for the NESTOR family of equipment was adequate when units were operating in one locale; when divisional units were dispersed (the normal practice), more keying devices were needed. The 101st Airborne Division recommended that keying devices for the KY-28 and KY-38 be supplied as required. In July 1969, II Field Force established a common NESTOR key list for all units operating in the III Corps zone. To maintain compatibility, key changes had to occur simultaneously in all units. The time chosen for this change was midnight, tactically the worst possible time because the greatest number of enemy contacts occurred from 2200 to 0200. Moreover, where several units shared the same keying device, having to move at night to change key settings was inconvenient and dangerous and added to the reasons for not using the equipment. Later the time of the daily NESTOR key change was moved to 0600.
As the use of communications security equipment increased in Vietnam, so did the need for logistical support. A reorganization was approved by the commanding general of U.S. Army, Vietnam, in mid-1967. The revised structure consisted of the Communications Security Logistics Support Center, Vietnam, which functioned as a general support facility serving U.S. Army, Vietnam, with six subordinate units strategically located in the four corps areas. The center was also assigned the mission of organizing, training, and deploying seven contact detachments to augment direct support to the combat divisions. Support began to improve.
Security codes were another problem. The early units had not been very conscious of communications security, and the unauthorized practice of using homemade communications security codes and shackles eventually became widespread. This dangerous practice; which persisted throughout the conflict and which gave users a false sense of security, was probably more dangerous than communicating in the clear. As the number of units burgeoned and the need for compartmenting code systems grew, U.S. Army, Vietnam, requested and received from the National Security Agency a whole series of preprinted codes to cover the expansion. These codes, while not perfect, were a great improvement in both the employment and distribution of such systems. Getting the infan-
tryman under fire, or the helicopter pilot supporting him, to employ the codes was another matter.
The continuing need for easier authentication and more reliable means for passing limited classified traffic led to a new development in the later stages of the conflict: the KAL-55B authentication wheel, or "whiz wheel," a circular authentication table in a plastic covered disc. This innovation simplified communications security measures to a level acceptable to most users.
Signal security, particularly in voice radio transmissions, was a major problem area throughout the period of combat operations in Vietnam. Army Regulation 380-40, Department of the Army Policy for Safeguarding Communications Security Information, assigns responsibility for this type of security to both the commander and the individual. All users of communications facilities were more or less aware of their vulnerability to enemy intercept, analysis, and decoding, and of the need for authentication and encoding. The gap between this knowledge and actual practice was immense, and in Vietnam it seemed at times an insurmountable problem.
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