Story 79 - COMSEC, Compromises

and  Changing Callsigns

November 1970 - November 1971

By Ken Mackenzie OAM



In late January early February 1971, I moved from Radio Troop into Communications Control, aka ‘Comms Con’.  Or, as many outsiders referred to us; “Ebony 106”, our telephone number. I was to ‘learn the ropes’ and take over from SGT Mike Didsman who’d been ear-marked to go to 3RAR, who were shortly to replace 7RAR.

It was a very steep and rapid learning curve.

Our manning consisted of 1xSGT Operator, 1xCPL/LCPL Operator, 1xSIG Draftsman and 1xCPL/LCPL/SIG COMSEC Monitor (when available).

Comms Con was the first point of contact for all 1ATF Radio, COMMCEN, Telephone, Line and Mail (SDS) issues. And it was a rare day that “Ebony 106”, didn’t ring…

Out of hours, Comms Con was manned by the 104 Sig Sqn Duty OFFR / SNCO.

One of our responsibilities was production and distribution of the monthly 1ATF Signal Operating Instructions (SOIs), including: Operations and Numeral Codes, KAC Codes and Keylists – including their delivery to our US Army allies, our far-flung Detachments and Liaison Officer (LO) Teams.

Another, was the ‘Daylight to Dusk’ monitoring the 1ATF VHF nets to capture poor voice procedure and security breaches. I would pass these to the OC 104 Sig Sqn via a weekly report.

Serious security breaches were always reported immediately.

In addition to monitoring radio nets, our “Ebony” Switchboard operators would always warn callers connecting to external Trunks that “The line is Not Secure, Sir”.

COMSEC monitoring took place in the Comms Con Bunker, located underground on the western side of the 104 Sig Sqn Sqn Headquarters building. It was accessed through internal stairs in Comms Con [this bunker contained a mirror-image radio set-up of the Radio Bunker on Nui Dat Hill and was designed to switch-over within moments, should ever the Radio Bunker be knocked-out or go offline. It was also where our Sqn Base Defence Net station was located and our “Stand-To” location, if we were attacked].

104 Sig Sqn
Photo 1 - COMMS CON radios being manned by L/CPL Brian Duncan in the 104 Sig Sqn bunker. 
Note the secure equipments KY-38 connected to 524 radios and remoted into the 1ATF CP.
 The equipment is used on the 1ATF Comd Secure Net and the 1ATF Commanders Secure Net.
(104 Sig Sqn Photo 4-5)

An operator would monitor all 1ATF VHF nets on a rotating basis, recording the voice transmissions on a NAGRA Tape Recorder. Security breaches would be noted as they occurred as well as the standard of users RATEL [Radio Telephone] procedure.

This monitoring was in progress when I arrived and from what I could see, was working well.

It was a surprise to read that 110 Sig Sqn blokes were doing this until March 1971. Perhaps I initially presumed they were Radio Troopers, or they were attached to Radio Troop. However, I’ve always been under the impression that our ‘bunker blokes’ were always Radio Troopers.

I would occasionally receive feedback from the OCs, MAJ Bergin / Roberts on some of the reports we submitted. Most instances were ‘brushed off’ by offending units, as being ‘immediate’ and ‘tactically necessary’.

An AN/GRA-39 Remote Unit tuned to the 1ATF Command Net, was located on a small shelf next to my desk. It allowed us to keep our fingers ‘on the 1 ATF pulse’ and could quickly be switched to the Battalion Command Nets.  A large, framed, acetate-covered Net Diagram of the 1ATF VHF Command Net, marked with current frequencies and all active callsigns, dominated the southern wall. On the opposite wall were Four ‘K’ Phones. They were direct lines to our defensive bunkers on our northern perimeter.

Compromise 1

On the 31 March 1971, elements of 3RAR contacted elements of D445 VC Battalion east of Nui Dat. I was following the transmissions and listened to the CO, flying overhead in his helo, berating one of his company commanders for taking too long to come up in support of the troops in contact. I can still recall the exasperated reply “…We’re caught in thick bamboo, Niner...!”

Photo 2 - 3RAR solders in South Vietnam early 1971 (AWM PJE/71/0237/VN).

At the conclusion of the battle, it was reported that a number of items were missing, including SOIs and possibly Codes.

When the initial contact occurred, the troops dropped their packs and ‘hooked in’. When they eventually returned, it was discovered that some of the enemy had circled around and looted the dropped packs.

The loss of the SOI and Codes had severe consequences. It meant that all 1ATF VHF communications were now completely compromised. It also meant a complete re-issue of a new SOI, new Operations, Numeral and KAC Codes, was now required.

 In my time in 1ATF, Callsigns and Frequencies changed weekly, and for ease of use, the monthly 1ATF SOI was produced in four, one-week blocks. Each A4 Page consisted of two smaller, individual ‘blocks’, which could be cut-out and slid into the sleeves of the green, plastic “Viewee-Twoee” field notebooks, that most carried.

This was also designed to lessen the possibility of a major comprise, as personnel operating ‘outside the wire’ were only supposed to carry sufficient of the active SOI to cover their time in the field.

Comms Con produced two, different, SOIs each month. One edition which was issued (Active SOI) and one edition which was held in reserve in case of Compromise (Compromise SOI). So, whilst the compromise SOI was quickly being distributed, Comms Con began production of two more 1ATF SOIs.

These were the days of manual typewriters, duplicating ‘skins’, correcting fluid and carnivorous Gestetner duplicating machines. Everything was done manually.

104 Sig Sqn SOI
Photo 3 - Page 1 and 2 of the compromised March 71 SOI  Note: The SOI has 114 pages.

Putting those bloody SOIs together was a particularly painstaking and time-consuming task. Every single item had to be ‘triple-checked’, every frequency, every frequency allocation, every primary frequency, every alternate frequency, every frequency designator, callsign, code-word, nickname, net diagram (carefully scribed by the draughtsman), unit name, etc., etc., etc., to ensure every item was 100% correct and there were absolutely no duplications – errors could cost people's lives. There could be NO mistakes whatsoever [and I might point out, that we created ‘from scratch’: every Callsign, Callword, Net Call, Nickname, Code-word, Address Group, Frequency Designator, Net Diagram, etc. There was also the critical issue of VHF frequency compatibility with ‘C’ Sqn’s Centurion Tank’s crappy British C42 Radios and our AN/PRC-25s, ‘77s and RT-524s. Why we never retro-fitted these tanks with AN/GRC-125s/160s, as a ‘Field Expedient’, has always confounded me.]

It meant re-typing, on a manual typewriter, a whole new skin where correcting fluid didn't work, and/or a particular item looked smudged, confusing or ambiguous.

And then there was the temperamental Orderly Room Gestetner Duplicator - it would always 'eat' several skins of every SOI - again more typing, rechecking and delay [this only changed when the inimitable Signalman Howard (Banjo) Patterson came to Comms Con. "Banjo" was our saviour; he was a Gestetner Technician/Salesman before he joined up. When he’d finished overhauling the Gestetner, it ran like a Swiss watch!].

104 Sig Sqn
Photo 4 - Gestetner AKA "Duplicator Machine Stencil Hand" from the period (Internet Source)

However, we worked right through the night and by 0900 hours on 01 Apr 1971, had two new SOI Editions. Then, it was simply a matter of collating and stapling 30/40 copies of each…

Compromise 2

The second major compromise occurred on 17/18 April 1971. The Vietnamese 302nd Regional Force Battalion was undergoing training by an Australian Mobile Advisory Training Team (aka MATT Team) and US Army Special Forces personnel in the Long Hai Mountains.

One of the Vietnamese soldiers was wounded by a mine, and a Dustoff was requested. Again, we were following the radio transmissions in Comms Con. A Huey Dustoff, escorted by Gunships was reacted from 8 Field Ambulance.

Tragically, in the process of winching up the casualty, the Dustoff suddenly came under heavy enemy fire and crashed in flames; killing the Army Medic on board, the casualty being winched, a MATT CPL and US ARMY CAPT on the ground, who’d been directing the Dustoff. The pilot, co-pilot and crew chief, managed to escape the burning Dustoff. However, medic was trapped and despite the frantic efforts of the crew chief, could not be rescued.

[The Army Medic was LCPL John Gillespie of 8 Field Ambulance. The Dustoff was totally consumed by fire, and he was listed as MIA. LCPL Gillespie’s remains were finally recovered in November 2007 and repatriated to Australia on 19 December 2007.]

John Gillespie comes home
Photo 5 - John coming home after 36 years in Nov 2007 (Reuters).

I was advised the next morning that the 1ATF SOI carried by the Dustoff Pilot could not be positively confirmed as destroyed, and was to be considered as compromised. So away we went again…

We’d produced four SOIs in 18 days. They were to be the last compromised SOIs in 1ATF's involvement in the Vietnam War.

Not long after this, I moved across to 4RAR as the Radio SGT.

Changing Callsigns and Frequencies

In my time, callsigns and frequencies changed at midnight every seventh day in accordance with the active SOI.

It was considered that the daily changing of callsigns was a waste of time, because the same operators were still using the radios, which negated any security value accorded by the new Callsign.

There was also the problem of Armor (Cavalry and Tanks) Artillery, and Engineers, who used fixed callsigns, which were also prominently displayed on their vehicles.

Then there were the Infantry Battalions. Our battalions used weekly-changing callsigns on the 1ATF Command Net. However, the Battalion Command Nets and Company Internal Nets used their standard callsigns: OA, OB, OC, 10, 20, 30, 40, 50, etc.

Moreover, changing frequencies more often wasn’t an option either. This was because there was a very limited number of VHF frequencies allocated to 1ATF by the US Army’s Headquarters II Field Force, Vietnam   (HQIIFFV). VHF frequencies were at an absolute premium. It was not at all unusual for the same block of VHF Frequencies to be issued to allied units in adjoining Provinces, as I found out.

We would often have US Army Helos operating in adjoining provinces, coming up on our nets. On most occasions they were kind enough to change to their alternate frequency. However, if they were in a ‘hot’ situation, Gunship, Dustoff, etc. We would change instead.

Security Breaches

In my time at 4RAR, I never received any external feedback on Battalion security breaches, although we were quick to point them out when they occurred internally.

Photo 6 - 4RAR on patrol in South Vietnam late 1971 (AWM CUN/71/0529/VN).

In this regard, LCPL Nick Mazzarol was the undisputed champion. After one hectic day of fighting, the Battalion believed we had the bad guys surrounded in a bunker system. At his evening Orders Group in the Battalion Command Post (Bn CP), the CO was briefing his Company’s, Platoons and other surrounding unit’s elements, of exactly where each was in relation to the other by direction and distance. The plan was to go in at first light and roll the bad guys up. Finally, the CO warned of the likelihood of probes as the enemy desperately looked for a way to exfiltrate his predicament.

So far, so good.

Later in the evening, one of the surrounding elements called for a Flare-Ship as it was being heavily probed, had no illumination, and the location of the other elements ruled out Artillery Illumination being used.

Nick was on duty in the Bn CP and passed the request on to HQ 1ATF.

When the Flare-Ship arrived ‘on-station’, the pilot requested a “Grid” to drop his flares. The CO passed him the requesting element’s grid reference in clear, the pilot read it back and dropped his flares.

Quick as a flash, Nick pointed out to the CO, that by passing that one unit’s grid reference in clear, he’d given away the locations of all the other surrounding units. This didn’t go over all that well…

Next morning, it was discovered that that the enemy had indeed managed to exfiltrate the bunker system, exploiting the larger gaps between our surrounding units.

Active Enemy Electronic Warfare against 4RAR/NZ (ANZAC) Battalion

It was not uncommon to have local ARVN (Army of the Republic of Vietnam) soldiers ‘come-up’ on your frequencies. They had a bad habit of scrolling through the VHF frequencies until they found a quiet one and would then start transmitting to each other. A few choice words were normally enough to get rid of them.

Photo 7 - ARVN soldiers deploying in 1971 with Australian soldier on APC watching (AWM PO7837.012).

In July of 1971, we redeployed from FSB Trish to Courtenay Hill in Southern Long Khanh province. From here, our battalion began operations east and west of Route 2 against the 274th (Mainforce) VC Regiment, D445 VC Battalion, 3/33rd NVA Regiment and local Guerrilla Units, such as the 13 Chau Duc, C36 Sapper Company and the K8 Support Company.

From late July, early August on, within minutes of our larger contacts being initiated, Vietnamese voices would ‘come-up’ on our Battalion Command Net and/or the fighting Company’s Internal Primary Frequency in brief, rapid conversation, disrupting the command and control of our troops in contact.

An immediate change to our Battalion/Company’s Alternate Frequency generally took care of the problem. However, changing radio frequencies in the midst of a battle is far from ideal and fraught with danger.

[We knew that the VC/NVA used captured AN/PRC-25/77 radios. And they certainly would have been listening to us. The distribution of our SOIs was wide enough for their intelligence network to get hold of our frequencies, too.]

In my view, these occurrences and their timing were way too regular to be accidental or coincidental. It would have given the VC/NVA enough quick breathing space to break contact and bug out. Or leave behind a rear-guard to give them cover and time.

These instances occurred mainly during our contacts on the western side of Route 2.


They were indeed interesting times.   Many of these memories are as fresh as yesterday.  I still dream I’m there… And strangely perhaps, wish I was.

Ken Mackenzie

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