SIGINT Success at the Battle of Loc An, 1969

547 Signal Troop (“the Troop”) was a sub-unit on the Order of Battle of the 1st Australian Task Force for the duration of the Vietnam War. Its role was to provide timely Signals Intelligence (SIGINT) to the Task Force, initially operating only as a “post office” for the US Army SIGINT organisation, but quickly becoming a significant operational SIGINT resource in its own right.

In an era before the Australian Army embraced Electronic Warfare (EW), which did not occur until the late 1970s (and strongly motivated by the Troop’s successes in South Vietnam), the Troop was under the operational control of USA Army Security Agencies (ASA) and required to operate under stringent strategic security regulations applying to the existence and distribution of SIGINT. This necessitated restricting the access to its end-product to a very small number of appropriately cleared recipients, many of whom, in the early days of the deployment had very little exposure to, or confidence in, the intelligence product being developed. This, together with the ‘fog of war’, was certainly the case in the lead-up to the Battle of Long Tan.

Photo 1 – The “Set Room” of 547 Signal Troop where radio communications of VC and NVA transmissions were intercepted (7 Signal Regiment (EW) Archives)

As a direct result of that battle, the Troop strength was doubled (from 15 to 30) and an R and D task (Project HIGH DIVINE) was initiated with the Weapons Research Establishment (WRE) to equip the Troop with its own high frequency Airborne Radio Direction Finding (ARDF) equipment, to be installed in the fixed-wing aircraft of 161 Reconnaissance Flight. Officially, the operations of the Troop continued to be “highly classified” as secret code word until the release of the three volumes of The Official History of Australia’s Involvement in Southeast Asian Conflicts 1948-1975, which contain numerous citations referring to the contribution of the Troop to Task Force operational planning.

In April 2012, the Defence Honours and Awards Appeals Tribunal (DHAAT) initiated an “Inquiry into the Recognition for Service with 547 Signal Troop in Vietnam from 1966 to 1971” to examine relevant evidence and consider appropriate recognition for the Troop’s contribution. A number of supporting submissions were made including a detailed Troop submission. This article expands on just one engagement reported in that submission ─ one that has yet to be recognised in any official record of the War.

Photo 2 – The prototype model of the indigenous ARDF equipment used by 547 Signal Troop, installed in a Cessna 180. The antenna pod was located behind the pilot’s seat and the DF console replaced the co-pilot’s seat with the DF operator in the rear seat. Plotting the location of the target transmitter was performed post-sortie and required complex calculations.

Much of the text in this article has been based on the recall of Troop members who were directly involved in the incident. The authors are particularly indebted to Adrian Bishop and Jeff Payne for their contribution. The italicised text is based on detailed historical research of North Vietnamese and Viet Cong records and unit histories undertaken by Ernie Chamberlain and focuses on the enemy view.

The strategic situation in May – June 1969
The communist headquarters in South Vietnam ordered a month-long campaign of ‘High point” attacks for the period 5 May-20 June 1969. Following the late-May announcement of the planned early-June meetings of Presidents Nixon and Thieu at Midway and the communists’ planned announcement of the formation of their Provisional Revolutionary Government, further significant attacks were planned. With the occupation of Binh Ba village by elements of the 33rd NVA (North Vietnam Army) Regiment on 5 June 1969, the Australian Task Force’s 5 RAR became involved in heavy fighting over several days in both Binh Ba (Operation Hammer) and Hoa Long (Operation Tong) villages.

274 Viet Cong Regiment – Plans Uncovered
In mid-June 1969, during normal radio frequency search operations, two experienced Operator Signals of the Troop, Corporal Roy Dean and Signalman Barry Nesbit, recognised ─ purely by its aural characteristics, that is to say, the ‘fist’ of the VC operator ─ the radio transmitter of the headquarters of the VC’s 274th Main Force Regiment which had been observing radio silence for several days. While Dean and Nesbitt copied the radio messages, the target frequency was also being monitored by Troop member, Signalman Jeff Payne, who was flying a scheduled ARDF mission in a Cessna 180 from 161 Reconnaissance Flight, piloted by Lieutenant Tony Sedgers. Sig Payne undertook the tracking procedure and immediately passed this data (via a secure voice link) to Sergeant Bob Hartley who performed the appropriate calculations and plotting to determine the location of the target transmitter.

This indicated that the radio station serving the headquarters of the 274th Regiment was located near a Thai Army forward base in Long Thanh District of Bien Hoa Province, 38 kilometres north-west of the Australian Tactical Area of Operational Responsibility (TAOR) but within the Australian Tactical Area of Intelligence Interest (TAOI).

One of the Troop’s cryptanalysts-linguists, Corporal Adrian Bishop, was able to decipher and translate the intercepted VC radio message. This was a rare event, given the enemy’s strong insistence on the use of unbreakable one-time-pad cipher systems. The message said, inter alia, “when the combat is over you are to evacuate the wounded to the hospital in the May Tao mountains as agreed at our planning meeting.” This single piece of intelligence indicated that a significant attack was imminent as the Regiment’s casualties were usually evacuated to the nearby Hat Dich Secret Zone.
The information was quickly passed up the chain to Bien Hoa, thence on to the Special Security Office serving the headquarters of 2 Corps, Field Force Vietnam (II FFV). After several urgent exchanges between intelligence staffs, it was agreed by all sides that the most likely target was the battalion base of the Royal Thai Army Volunteer Force (RTAVF) 2nd Infantry Battalion/1st Brigade/Black Panther Division located at Loc An ─ about 3.5 kilometres south-east of Long Thanh District town and 28 kilometres east of Saigon. This Thai position was defended by two companies, numbering 245 personnel, and included a US SNCO as a liaison officer. Arrangements were quickly made to harden the defences of the Thai position and prepare for the attack.

The Attack
At about 1.00am on the 16 June 1969, the VC Commander ─ Nguyen Nam Hung ─ launched his attack on the Thai perimeter with two battalions plus sappers and one battalion and RHQ in reserve. A barrage of VC mortars and rocket propelled grenades was followed by three waves of ground assaults and greatly outnumbered the Thai defenders. However, the attackers were taken completely by surprise and were repulsed with a bewildering amount of firepower including small arms and mortar fire, artillery support, claymore anti-personnel mines, helicopter gunships as well as other US close air support ─ including napalm. The battle raged for several hours but the defensive fire was so intense and casualties so high, the VC Commander was forced to call off the attack and retreat.

By coincidence, the Troop’s senior traffic analyst, Staff Sergeant Darryl Houghton, was visiting a fraternal American intercept organisation unit at Bien Hoa and was due to return to Nui Dat later on the morning of the attack. The Americans were so impressed by the intelligence tip-off and the successful defence of the Thai position, they diverted Houghton’s helicopter to the site of the battle. Houghton arrived just as the body count was completed; 212 enemy bodies were found. The fire from the helicopter gunships and the base defenders was so intense that the VC were not able to drag away the bodies of their KIA as they routinely did during other battles. Thai casualties in this battle were 6 killed and 34 wounded.

Photo 3 – Thai troops examining captured 274 VC Regiment weapons after the unsuccessful attack at Loc An, 16 June 1969 (US Vietnam Centre and Archive – No. WA001107)

In subsequent notification, the 1ATF intelligence staff reported that the action “resulted in 212 enemy KIA and one enemy POW … Numerous individual and crewserved weapons, ammunition and other materials were captured. Captured documents identified the elements of all three battalions of 274 Regiment, K21 Sapper Reconnaissance Company and rear elements of 274 … This assault … has probably rendered the Regiment marginally effective as a regimental-size combat force. It is assessed that remnants of the Regiment have withdrawn to their Hat Dich base area and will probably remain there for at least a month, until replacements are received”.

Subsequently, and based on the Troop’s information, the Task Force Commander (Brigadier Sandy Pearson) directed ambush action on the expected 274 Regiment withdrawal routes eastward to the May Tao base area. Successes were reported a few days later. “Early am on 20 June 1969, 6RAR elements ambushed a 50- strong VC group moving from west to east, killing 22 at YS498896 [east of Route 2 and just inside Phuoc Tuy Province] ─ captured documents tentatively confirmed the 2nd Company of 274 Regiment’s 1st Battalion.” A VC POW confirmed that the group had been engaged in evacuating wounded from 274 Regiment following their unsuccessful attack on the Thais. While the ambushing elements of 6RAR had been positioned there on the basis of the Troop’s earlier intercepts, this is not acknowledged in any history. Hence the excellent teamwork resulting from this one intercepted encoded message, and the accurate ARDF fix, resulted in 234 enemy KIA in just four days.

Yet the background behind the attack on the Thai position in June 1969 does not appear anywhere in the annals of Australian (nor apparently in Thai) military history. As Ernie Chamberlain has noted in his writings: Perhaps understandably, the failed attack on the Thai position is not mentioned in any published Vietnamese histories of the War, including in the history of 274 Regiment’s higher headquarters, the 5th VC Division and Military Region 7, nor in the recent memoir of the 274 Regiment Commander, Nguyen Nam Hung ─ now a retired Major General. Further research of Vietnamese documents reveals that the C.12-65 Binh Gia Assault Youth Unit from Phuoc Tuy province was involved in portering the 274 Regiment casualties eastward to the May Taos. And there was a brief Hanoi account in an article titled: “Dazzling Military Feats During June” and dated 1 July 1969 ─ “On 15 June, the PLAF of Bien Hoa Province destroyed a battalion-size unit of Thai troops near Long Thanh”.

It is almost certain that the recipients of the “tip off” in the Thai perimeter that night were never told that the source was from an Australian intercept. The story is only known to a handful of people outside of the Troop, mostly Americans in the SIGINT community.

Lessons Learnt
Tactical SIGINT is timely and potentially ‘actionable’, but extremely perishable as events move quickly. Quite often, it is not possible to verify this intelligence by other means. The above incident is just one example where the Troop expeditiously passed information to relevant combat forces needing the information. Their timely and effective reaction to that SIGINT turned a potentially disastrous situation into a highly successful outcome.

In June 2015, the DHAAT published its Report. While acknowledging the outstanding achievements of this small RASigs unit, the Tribunal determined that any unit type recognition would create a difficult precedent and consequently have an adverse effect on the Defence Honours and Awards system. However, in September 2018, the Australian Minister for Defence Personnel announced the award of the Republic of Vietnam Cross of Gallantry with Palm Unit Citation, this recognition flowing on from being under the operational control of US ASA units which had been so honoured way back in the 1960s. While there is never likely to be any Australian Government recognition, it is at least gratifying to the Troop’s members that just some aspects of their contribution to Task Force operations have now been acknowledged in the Official Histories.

By Lt-Col (retd) Steve Hart and Brigadier (retd) Ernie Chamberlain for MHHSNSW Journal – Reconnaissance Winter 2019

Footnotes for this article are available on request.
Brigadier Chamberlain was a 1 ATF intelligence liaison officer in mid-1969.

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