Past, Present and Future of Tactical Radios – Part 7

Continuing from Part 6 – As related in the earlier post, some factors facing the post-Vietnam Army that influenced the development of tactical communications included:

  • Force structure changes
  • Need for a proper squad radio
  • Increased communications security requirements
  • Digitization of the battlefield
  • Need for even more reliable hardware

The force structure changes affected tactical communications in two regards.  First, communications staff within the line units diminished.   Radio operators (MOS 31C and later 25C) held slots down to the line companies.  After experience with easily operated AN/PRC-77s in Vietnam, these slots became bartering chips in a larger game of personnel allocations.  The Signal Corps needed personnel to man the new division/corps/theater multi-channel communications network.  As the Army moved from the H-series to J-series TOE, the combat arms gave up radio operators in order for promised coverage by mobile field phone service from the divisional signal battalion.  In the “new” army, radios would so simple to operate, everyone would be an RTO.

Reorganization also reduced the number of radio repairmen and logistic support.  By the time of the J-series TOE, line companies lost their radio repair specialists (MOS 31V), consolidating them within a 15-20 man battalion commo section.   Also with changes to the support system, the repair system authorized fewer radio module substitutions at the battalion level.  The army consolidated the specialized technicians and the bench stock of repair parts at the divisional and higher level.

To resolve the shortfall at the squad level, the USMC developed the AN/PRC-68, with initial fielding in the mid-1970s.  The radio operated between 30 and 79.95 Mhz, with a 50 khz channel separation, making it compatible with the platoon radios.  It offered a range of 3 to 5 km.  The initial model had some limitations due to the antenna matching.  Improvements lead to the PRC-68A and B models that resolved the antenna problems among other things.  The Army continued development into the AN/PRC-126, which expanded the upper range to 87.975 Mhz with a 25 khz channel separation.  The 126’s arrived in units from the mid-1980s on.  These true “handie-talkie” descendants weighed only three pounds, even with the rare KYV-2 secure module attached.

The PRC-68s and 126s were for the most part good hardware.  But from an operator’s standpoint, frequency changes on the PRC-126 in particular was time consuming – sort of like setting an alarm clock waiting for the right number to increment.  In bad lighting, the display could be hard to read.  And there were the batteries.  The BA-5588 was rather light, so nobody complained about carrying a few extra.  But when the power ran low, the radio gave off an annoying warning beep.  And the batteries always seemed short in supply.   Lastly, with the withdrawal of the communication specialists from the line, the quality of operator maintenance dropped off.  (Although I heard a lot of interesting “a dog ate the radio” stories because of this.)

Although non-tactical according to the book, many units turned to commercial equipment for “hand held” radio needs.  Two examples, that I became well acquainted with, were the AN/PRC-127 and Motorola Saber radios.   Both types featured rechargeable batteries and were easy to use.  But the radios operated on non-tactical frequencies and were not designed to be kicked about.  Although many infantry units attempted to use these radios on exercises, the type was best suited for garrison work.  However, these radios were examples of early wide-scale use of commercial-off-the-shelf (COTS) radios.

Turning to the communications security issues, the Army replaced the old NESTOR systems with KY-57 VINSON encryption devices starting in the early 1980s.


The KY-57 weighed five pounds, perhaps six with a BA-5590 battery for power.  Dispensing with the unpopular pins and paper of the NESTOR system, the operator loaded an electronic crypto variable into KY-57 with either a KYK-13 or KYK-15 fill device (which were filled with a temperamental KOI-18 tape reader).

KYK-13 on display at the National Cryptologic ...

Putting a KY-57 into operation required specific steps, executed in sequence.  But the sequence was easily learned (arguably easier than field stripping an M-60 machine gun!).   Kits allowed the KY-57 to secure the VRC-12 series and PRC-77 radios.  The backpack kit’s cables stood up well (in my experience at least).  On armored vehicles, because no space was allocated when the tanks and APCs were designed, the kits required cables to be jammed into cramped spaces.  And vehicle mounts required a “J-Box” stacked under the radio set.  J-box replacement required repairmen to disassemble the entire mount.  Both the KY-57 and the fill devices used a hold up battery (HUB), designated BA-5372, about half the size of a standard AA battery.  The HUB lasted about a month under normal conditions.

Generally the KY-57 was a “grunt proof” device.  About the only serious complaint was the handling of the crypto variable.  Variables could be corrupted or mis-matched.  Over-the-air rekeying was an option, but was rarely practiced.

The KY-57 addressed the threat of enemy intercept, but left the radios vulnerable to jamming and direction finding.  In the early 1970s the Army did identify the solution as frequency hopping (a concept invented by actress Hedy Lamarr, by the way!)  But the state of technology at that time could not deliver a radio using frequency hopping.  But the requirement became the prime feature for the next generation radios entering advanced development in the 1980s.

The Army also demanded the next series of radios support digital data exchanges.  The internet was barely more than a backbone network, yet the Army had already begun fielding the TACFIRE system controlling field artillery fires.  Also the air defenders used a Target Alert Data Display System (TADDS) to provide information from search radars to gunners.  While the VRC-12 series could support data transmissions, the data-rate was relatively slow.  Any new radios had to support fast (for the time) baud rates.

Arriving concurrently with, and largely enabling, this digital revolution, semiconductors, integrated circuit (IC) components, and micr0-chips became common place in the mid-1970s.  Pocket calculators became affordable, and the home computer was not far around the corner.  Just as the transistor overcame the limitations of the vacuum tube, the micro-chip supplanted the transistor.  The military was quick to identify the advantages of the new electronic components.  Not only could more circuitry be packed into a smaller package, but the components had a longer mean time between failures.

Through the 1980s, the Army focused on a new radio system using the new semiconductor technology to address security, digital data, and durability requirements.  This path lead to the subject of my next post – the SINCGARS radio series.

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