The Role of Signals Intelligence in Australian Military Operations, 1939–72
* This article is based largely on extracts from the author’s book entitled Signals: Swift and Sure—A History of the Royal Australian Corps of Signals 1947–1972, Royal Australian Corps of Signals Committee, Melbourne, 1999.
With the Australian Defence Force’s (ADF) heightened operational tempo over recent years, analysis has been focused on the role of traditional combat arms and combat support elements during military deployments. Soldiers have given comparatively little thought to one of the most significant, but little-understood, combat-power multipliers of the Army, namely signals intelligence. In many respects, signals intelligence has been the poor cousin of human intelligence. In the 1990s, for instance, the benefits emanating from human intelligence were apparent to Australian commanders through operations in Somalia, Bougainville and East Timor. Yet historically, signals intelligence also has been a significant, albeit highly secret, combat asset, with its responsibilities shared between the Australian Intelligence Corps and the Royal Australian Corps of Signals.
One of the reasons that an awareness of the importance of signals intelligence has not registered more prominently in the Army’s consciousness has been the fact that, following the end of the Vietnam War in the early 1970s, there was a lull in operational deployments until the early 1990s. Yet, despite the role that signals intelligence has played in recent operations, notably in East Timor in 1999, it remains an asset that is not well understood by many in the Australian Army. This article provides a historical review of signals intelligence since World War II. It argues that signals intelligence deserves closer attention and greater appreciation by land force commanders and their staffs. While security considerations prevent a discussion of signals intelligence’s direct application on recent and current operations, a brief historical overview of the capability’s role may help commanders and operational planners better appreciate what remains an enigmatic but important operational asset. In the history of the Australian Army, signals intelligence played a significant role throughout Cold War-era operations in Malaya, Borneo and Vietnam and previously during World War II.
Australian Signals Intelligence in World War II
During World War II, a number of special-function signal units were raised in Australia. These units included the New Guinea Air Warning Wireless Company and Special Wireless (or electronic warfare) Signals units. As early as December 1939, a signals detachment from the militia’s 3rd Division in Melbourne had been detailed to intercept enemy wireless transmissions. In June 1940, No. 1 Australian Special Wireless Section was formed in Seymour, Victoria, in order to intercept and evaluate enemy wireless communications.
In 1941 the unit, now renamed No. 4 Australian Special Wireless Section, commenced operations in the Middle East as part of the 1st Australian Corps. In February 1942, with the onset of the Pacific War, the section was posted back to Australia in order to monitor Japanese signals traffic.1 During 1941, several additional small signals intelligence sections were established in Australia, including an organisation designed to crack Japanese codes at Sydney University, although it was the intelligence efforts of the Royal Australian Navy that ultimately succeeded in this endeavour.2 The Australian Army’s signals network expanded during the war under the direction of two complementary organisations: an intercept organisation and a research-and-control centre. The electronic interception organisation, incorporating the bulk of the No. 4 Special Wireless Section, came to be known as the Australian Special Wireless Group. The research-and-control centre, established in Melbourne in April 1942, became the Central Bureau and included a mixture of Australian Army, RAAF and US Army personnel. By 1944, the Central Bureau was intercepting and transcribing ULTRA information on a prodigious scale, thus contributing significantly to the successful conduct of Allied military operations. The unit’s success was mainly due to the application of both traffic analysis and cryptography. Traffic analysis involved the study of enemy wireless circuits, call signs, procedures, traffic volumes and messages that were intercepted in plain language. In addition, cryptography, involving the breaking of enemy codes and ciphers, combined with translation, derived a great deal of useful intelligence material—much of which was shared with the Allies.3
During World War II, there was close coordination at the highest level of signals intelligence between Britain and the United States. This coordination was gradually extended to include Australian and Canadian code-breaking facilities.4 In the Pacific theatre, as in the European theatre, the breaking of the enemy’s codes proved vital in turning the tide of war in favour of the Allies. In fact, the role of the ULTRA code-breaking system, which was derived from enemy high-grade ciphers, was recognised as being decisive by the Allied high command. As General Willoughby, General Douglas MacArthur’s intelligence chief, put it, ULTRA ‘cut two years off the war’. Information from ULTRA dramatically shaped Allied strategy, enabling their forces to pre-empt Japanese military actions repeatedly.5
The Early Postwar Era: The Formation of the Special Wireless Regiment
In December 1947, the wartime success of signals intelligence persuaded the Chifley Government to authorise the integration of the various Australian agencies into the United States and United Kingdom (UKUSA) system that also included Canada. This agreement helped create what Australian scholars Desmond Ball and David Horner describe as ‘the most important secret intelligence co-operation regime ever organised.’6
The postwar Australian Army also recognised that the most important means of gathering information about an enemy in any future conflict would be by deciphering intercepted signals.7 Consequently, the Army’s establishment included, for the first time, a unit that was raised in peacetime and was designed specifically for signals intelligence. The unit concerned was No. 101 Wireless Regiment, originally commanded by Major T. R. (Dick) Warren, and based at Cabarlah near Toowoomba in Queensland.8 Cabarlah, which began operation in the course of 1947, was to become the permanent home of Army signals intelligence.9
The new Wireless Regiment’s operational tasking was controlled by the Joint Services organisation in Melbourne. Operational, as opposed to administrative, control was exercised by the Defence Signals Bureau in Melbourne, later renamed the Defence Signals Directorate (DSD).10 During this period, No. 101 Wireless Regiment’s main role was the strategic interception of telecommunications from, and within, the Asian region.11
In terms of the Army signals intelligence, the fact that operational control of No. 101 Wireless Regiment—renamed 7 Signal Regiment in late 1965—was vested in an external agency meant that the unit was divorced from the mainstream of the Army. Nonetheless, the Wireless Regiment did participate in Army exercises. In April and May 1959 in Exercise Grand Slam, a regimental detachment was included as part of the notional enemy force opposing the 1st Independent Infantry Brigade Group. One participant observed that, despite the limited time involved in which to exercise electronic countermeasures,
We [in the detachment] were able to very rapidly... work out the communications ‘nets’ and the ‘order of battle’ of the enemy and we had it down pat within 36 hours (it goes to show how bad some of [the Army’s] protective measures were). We carried out fairly effective jamming, so much so, that the opposing brigade signals officer complained, so we were ordered to stop in order to allow the exercise to proceed... One of the nasty things we could do was to tape-record rendezvous points for orders groups, fire orders and other important administrative messages, and, with minor alterations, play them back on the same net, thus creating a tremendous amount of confusion—it’s a dirty trick! The result of that was that the higher levels of the Army became aware of the great potential of electronic warfare to disrupt [their] command and control [in battle].12
Following Exercise Grand Slam, the Wireless Regiment adopted a policy of ‘passive’ electronic countermeasures, involving mainly listening as opposed to interference procedures. The regiment adopted such an approach because the prevailing philosophy emphasised the importance of gaining intelligence rather than engaging in jamming and active counter-electronic measures.13 As one signals intelligence specialist, Peter Murray, later explained, ‘jammers were great in a battle, if you were winning, but they [also] reveal your presence and it’s much better to be a silent listener, not revealing your presence’.14 Traffic analysis and cryptography sections processed information derived from intelligence sources in the Wireless Regiment. Traffic analysis personnel examined the network system building ‘net’ (user network) diagrams and establishing frequencies, call signs and other technical information from which an ‘order of battle’—a list of units, command structure and organisations in a given activity—could be established.
Apart from exercises, the Army also gave signal operators the opportunity to demonstrate their skills when they helped to detect that a coup was likely to occur in Indonesia on 30 September 1965. Australian signals specialists intercepted an enormous volume of traffic from Indonesian networks, including news of the murder of many senior military officials as a precursor to a coup. In terms of cryptography, encoded messages were intercepted, broken and assessed by linguists.15 Peter Murray recalled:
I got into awful trouble because it was a Friday night and I turned on the [communications] link, but I could only raise one very co-operative warrant officer (who had had a few drinks) at 4 Signal Regiment in Brisbane. We subsequently passed an enormous amount of traffic down the line to Melbourne...16
The Wireless Regiment also participated in various Australian overseas military commitments during the 1950s. For instance, from 1951 to 1959, 101 Wireless Regiment maintained a detachment in Singapore and Malaya as part of the 1st Australian Observer Unit. The detachment was a Wireless Troop type ‘F’ and included one officer and fifteen other ranks from the Regiment.17 According to one officer, the detachment ‘roamed around the jungle doing tactical intercept of Communist Terrorist communications (of which there were not a great deal)’.18
Signals Intelligence in Borneo
Between 1959 and Confrontation in 1964, the signals intelligence detachment in Singapore was initially known as 201 and then 121 Signal Squadron. The squadron’s wireless intercept role was such a well-kept secret that even many military personnel did not know that it performed radio intercept and analysis tasks for intelligence purposes.19 Indeed, following the Labor Party victory in the Australian Federal election of 1972, the newly elected Prime Minister, Gough Whitlam, caused a stir by publicly announcing the previously secret nature of the roles and tasks of 121 Signal Squadron. Shortly afterwards, the forces stationed in Singapore were withdrawn.20 However, by the time of the withdrawal, another set of operational experiences had been added to the Australian Army’s signals intelligence credentials in Borneo and later Vietnam.
During Confrontation in August 1964, the Australian Government gave approval for 693 Signal Troop to be deployed to perform wireless interception in place of a British Army signal troop. The Australians were deployed to the island of Labuan, off the coast of Sabah, and personnel from Australia’s Singapore-based 201 Signal Squadron staffed the troop.21 On Labuan, the troop provided valuable intelligence information, and following the end of Confrontation its personnel were reabsorbed into 201 Signal Squadron.22
Operations during Confrontation were successful largely because the intelligence information gathered from wireless intercept and interrogations was combined with the effective tactical application of that information. In Borneo individual patrols benefited directly from information received by electronic interception. Britain’s Director of Operations in Borneo was noted as having praised the signals intelligence effort during Confrontation as being a significant force multiplier that helped wrest the initiative in favour of the British and Commonwealth forces.23
Signals Intelligence in Vietnam
As Confrontation was winding down, and with the lessons of Borneo in mind, signals intelligence was once again called on to assist in the conduct of Australian military operations. In 1966, following the build-up of the Australian combat force contribution in Vietnam, Australia was allocated its own brigade-sized Tactical Area of Responsibility (TAOR) in Phuoc Tuy province. There the First Australian Task Force (1ATF) included 547 Signal Troop. The troop consisted of two officers and thirty-five other ranks and, from 1966 until December 1971, was located in the signals sector alongside the Task Force Signal Squadron at Nui Dat in South Vietnam.24
547 Troop and the Battle of Long Tan
547 Troop conducted the initial operations from Nui Dat in 1966. It aimed to secure the base area and destroy any Viet Cong installations in the area of operations. From mid-July to mid-August 1966, battalion group operations tried to expand the controlled area. On 18 August, D Company of 6 RAR fiercely fought its famous battle against the North Vietnamese 275 Army Regiment (NVA) in the Long Tan rubber plantation 3 km to the east of Nui Dat. By the following day the enemy dead totalled 245, and D Company 6 RAR had suffered eighteen dead and twenty-five wounded.25
Signals intelligence had begun revealing unusual enemy activity to the east of Nui Dat in late July 1966. Indeed, before the battle of Long Tan, 547 Signal Troop operators monitoring radio traffic had detected enemy activity. It was, in fact, the NVA that had been located, but the members of the taskforce had not realised this situation at the time. No enemy radio network suggesting the presence of such a large formation had yet been pieced together from the signal intercepts that the Australians were monitoring, and the enemy was, in any event, using runners between two of the battalions in the regiment.26 It was only on 14 August that signals intelligence personnel informed Brigadier Jackson that 275 Regiment was within 5000 m of the taskforce base. In response, Jackson ordered company patrols into the area where 547 Signal Troop had reported the possible location of 275 Regiment. The patrolling did not reveal any signs of enemy activity until the actual engagement at Long Tan commenced on 16 August.27 Consequently, as McNeill notes:
[Brigadier] Jackson can hardly be criticised for ignoring supposed evidence regarding the presence of 275 Regiment. Priorities were nevertheless convoluted, and in this instance could have led to catastrophe, when the need to protect the nature of SIGINT weighed more heavily than the need to inform [the Commanding Officer of 6 RAR, Lieutenant Colonel] Townsend of the suspicions it had engendered.28
One of the results of the battle of Long Tan was that Australian and Allied staff officers were increasingly attentive to information derived from signals intelligence.29 Nonetheless, significant communications problems continued during the Vietnam War, often because of the poor standard of Australian and Allied communications security—a shortcoming that made eavesdropping a relatively easy and profitable task for the enemy.
The Australian Army, however, made the best use of its equipment to engage in its own limited eavesdropping operations. In particular, 547 Signal Troop provided special communication facilities, often under hazardous conditions, and became an intermediary between Allied radio research units and Australian Task Force Headquarters. The troop operated under the strategic control of the US signals intelligence organisation in Vietnam through an Australian Defence Signals Directorate (DSD) liaison officer. Nonetheless, the troop provided valuable tactical information, enabling the United States to take effective counteraction against the Viet Cong and North Vietnamese Army.30 The troop conducted independent ‘communications research’, using antennas made of ‘star pickets’ welded together to a height of about 35 ft. The up-to-date information that the troop gathered clearly indicated the extent to which information coming from other sources had been superseded.31
In Australia, a special Pre-Vietnam Orientation Course was set up at the Army’s signals base in Cabarlah in order to prepare replacement operators for the unique and difficult intercept role in South Vietnam. The course used live tapes sent back by 547 Signal Troop. Meanwhile, the troop manned a ‘set room’ with technical maintenance, a ‘single-station locator’ cell and other complex equipment, including computers for processing information gathered.32 In fact the demand for such processing increased as the war continued on the ground and in the air, and collection methods improved.
Vietnam: Airborne Collection
An important development in signals intelligence in Vietnam was the Weapons Research Establishment’s accurate airborne radio direction finder (ARDF). According to Peter Murray, the Officer Commanding 547 Signal Troop in 1968, the ARDF was probably the single most important intelligence gatherer apart from the ‘eyeball’ of infantry patrols.33 Early in 1967, the troop began to conduct aircraft experiments by using the new equipment.34 Once equipment tests proved effective, a pattern was established based on using ‘shush’ flights with Cessna aircraft that could be flown up to six times per day in order to eavesdrop on enemy radio traffic. The aim was to try to pinpoint enemy headquarters and unit locations for taskforce intelligence and operations staff involved in planning. The name ‘shush’ came about when the Officer Commanding was asked by a senior officer visiting the flight line, ‘what’s the Cessna with all the electronic equipment inside it for?’ The reply to the senior officer was ‘shush, we can’t talk about it.’
The success of Cessna ‘shush’ flights depended on the aircraft flying steadily at the same speed, height and bearing. This uniformity was necessary for a manually operated directional antenna pod under the plane to take a series of ‘listening shots’ (giving bearings and time along the flight) about the enemy’s location, and the entire process yielded accurate information.35 Murray recalled:
If we knew the location and type of unit we would sometimes say ‘leave it alone’. On one occasion the [Special Air Service] went out and took a radio station which had 14 people. They came out with the radio set and their cipher books. The cipher books opened up a lot of information to us.36
The resources available to the Australians for these missions were small in comparison to those of their American counterparts. For instance, the Americans had at their disposal the aviation arm of the 1st Signal Brigade composed of forty- five aircraft. In contrast, the Australians relied on two aircraft from 1 ATF’s 161 Reconnaissance Flight, both of which had to be flown on a level straight course purely on instruments—a dangerous mission at that height over enemy-occupied territory.37 Although the Americans used similar aircraft, usually Otters— and later U-8 and RU-21 aircraft— their aircraft bristled with antennas. As a result, the enemy could easily realise what an aircraft’s mission was once the aircraft appeared overhead.38
On one occasion a Viet Cong ambush was discovered in the area over which an Australian reconnaissance aircraft was flying. A US company of infantry was moving towards it, and at Troop Headquarters two Australians, Captain Hugh Nichols and Corporal Ron Biddle, worked frantically to ascertain the identity of the troops moving into imminent danger. Operational files showed the company to be part of the US Army’s 199th Light Infantry Brigade. Word was immediately passed via the aircraft system to the US brigade headquarters that was able to redeploy the company and mount a counter-ambush. In the ensuing engagement, thirty Viet Cong and one American soldier were killed. Later, the company commander sent a message of thanks to the Australians, endorsed by the brigade commander with the comment ‘instead of a US body count we were able to do a VC count’.39
547 Signal Troop’s success in signals intelligence caught the attention of the US Commander, II Field Force, Vietnam, Lieutenant General Bruce Palmer Jnr. Realising the accuracy of the Australians’ information, General Palmer insisted on sending an American liaison officer to the troop in order to exploit their signals intelligence. Palmer believed that his own organisation’s reports were too vague—a view shared by fellow commanders of the US 9th Infantry Division and 11th Armoured Cavalry Division working near the Australians.40 An Australian signals expert observed:
The signals intelligence soldiers who did repeated tours of duty overseas may only be described as a highly dedicated group of soldiers. They were held in very high regard by all other nations at the highest level.41
Yet, despite the accuracy of the signals intelligence gathered, on its own such intelligence could not win the war for the Americans. At best, access to signals intelligence contributed to minimising the fog of war and simplifying the complexity of operations.
Ground-Based Innovations
The complexity of operations in Vietnam continued to stimulate innovation in electronic eavesdropping. For example, signals operations began experimental work in 1968 when a site north east of Nui Dat Hill was cleared for a new installation nicknamed ‘cell’. Aerials and airconditioned equipment shelters along with a computer were installed to investigate the ionosphere.42
Experimental work commenced in conjunction with the Weapons Research Establishment in search of a ‘single station locator’. The approach was based on the World War II German Wullenweber aerial system erected in a circle. The aim was to detect the source of a radio wave by measuring the phased time and angle difference between two incoming radio waves striking the antennas in the circle. The angle of deflection from the ionosphere was then calculated.43 According to Lieutenant Colonel Whyte, the techniques followed at Nui Dat were very successful in reinforcing the utility of signals intelligence.44
By late 1968, the taskforce’s forward deployments had resulted in the use of armoured command vehicles by the Task Force Signal Squadron. One of these vehicles, equipped with appropriate communications, was issued to 547 Signal Troop in order to ensure that, wherever the force deployed, signals intelligence support would be available. It soon became a part of standard operational procedure for the 547 vehicle to accompany the Task Force Headquarters and Signal Squadron on forward deployments. The appellation ‘547 Airmobile, Cavalry and sometimes Signal Troop’ jokingly came into being.45
The combined efforts of the employment of an airborne radio direction finder, a single station locator and a deployable armoured command vehicle ensured that 547 Signal Troop’s contribution to the Australian Task Force was far greater than its size suggested. The high profile of signals intelligence declined in the Australian Army following the end of the Vietnam War. However, it is clear that the capabilities demonstrated in South-East Asia remain valid.
Significance for Today
This article has sought to demonstrate the importance of signals intelligence by briefly surveying its history in the Australian context between 1939 and 1972. Today, as the Army grapples with how best to operate in a much more technologically complex era, it is even more important for operational commanders and their intelligence staff to appreciate the value of signals intelligence both for situational awareness and for time-sensitive combat support.
Indeed, perhaps the most significant area in which communications technology has had an impact on the conduct of military operations is in the area of signals intelligence. In World War II the Allies introduced the techniques of signals intelligence, with great strategic effect. As technology improved, that capability could be deployed to provide support down to the lowest tactical levels. In the Australian context, the conflict in Borneo demonstrated this fact—although only a few key individuals at the time were made aware of its significance. For the first time in the history of Australian military operations, the effectiveness of signals intelligence led to a brigade-sized formation (1ATF) having its own signals troop assigned to it in order to provide direct tactical signals intelligence support. That troop’s effectiveness ensured its retention as part of 1ATF. As the land force moves towards the Hardened and Networked Army, the utility of signals intelligence support will almost certainly increase in importance. In this sense, the lessons of yesteryear retain considerable value in providing a guide to the future.
Endnotes
1 The unit was later re-designated as 5 Special Wireless Telegraphy Section in February 1942.
2 For a detailed account of the significance of ULTRA to the allied effort in the Pacific and the contribution of the Australian Special Wireless units see Geoffrey Ballard, On ULTRA Active Service: The Story of Australia’s Signals Intelligence Operations During World War II, Spectrum, Richmond, Vic., 1991. See also D. M. Horner, High Command, Allen & Unwin with AWM, Canberra, 1982, pp. 224–7.
3 Ballard, On ULTRA Active Service, pp. 36–7; 146–7; 253.
4 Ibid., p. 275.
5 F. W. Winterbotham, The Ultra Secret, Weidenfeld and Nicholson, London, 1976, pp. 168–75; 191; 290.
6 Desmond Ball and David Horner, Breaking the Codes: Australia’s KGB Network, Allen & Unwin, Sydney, 1998, p. 2.
7 CRS A816, 43/302/18, Defence Committee Minute No. 10/1940, 15 February 1940 cited in Horner, High Command, p. 224.
8 Royal Australian Corps of Signals Museum (RASCM), ‘7th Signal Regiment Unit History’, prepared by Captain S. W. Foley, June 1986.
9 Theo Barker, Signals, p. 166; and MP 742, 240/7/388, ‘Australian Corps of Signals: Unit Nomenclature’, 22 October 1947.
10 K. Whyte, interview with author, August 1989; and Desmond Ball, Australia’s Secret Space Programs, pp. 2–3.
11 Interview with Lieutenant Colonel K. Whyte, August 1989.
12 Ibid.
13 Ibid.
14 Interview with Peter Murray, former Officer Commanding 547 Signal Troop, in Vietnam in 1968 (August 1989).
15 Ibid.
16 Ibid.
17 RASCM Minutes of D Sigs Staff Conference: Held at ‘Grosvenor’, 6 September 1955; and RASCM 101 WS Regt, Monthly Report to D Sigs, October 1953.
18 Interview with Lieutenant Colonel K. Whyte, August 1989.
19 Interview with Brigadier K. P. Morel, August 1989.
20 Robert O’Neill, ‘Defence Policy’, in W. J. Hudson (ed.), Australia in World Affairs 1971–75, George Allen & Unwin, Sydney, 1980, p. 11.
21 Staff Sergeant J. E. Danskin letter to the author, September 1989; and interview with Daskin, October 1989.
22 Danskin, letter to the author, September 1989; and interview with Ron Ratchford, August 1993.
23 Ron Ratchford, interview with author, August 1993.
24 RACSM, ‘7th Signal Regiment Unit History’; Murray interview, August 1989; and Davies, ‘A History of 547 Signal Troop in Vietnam’, p. 2.
25 The battle of Long Tan is covered in detail by Ian McNeil in To Long Tan: The Australian Army and the Vietnam War 1959–1966, Allen & Unwin and Australian War Memorial, Canberra, 1993. See also Lex McAulay, The Battle of Long Tan, Arrow Books, London, 1987; and T. Burstall, The Soldier’s Story, University of Queensland Press, Brisbane, 1986.
26 Murray, interview, August 1989.
27 McNeill, To Long Tan, pp. 307–11.
28 Ibid., p. 360.
29 RASCM, ‘A History of 547 Signal Troop in Vietnam’, unpublished manuscript, p. 4.
30 Whyte, interview, August 1989.
31 RASCM, ‘7th Signal Regiment Unit History’; and ‘A History of 547 Signal Troop in Vietnam’, pp. 2–4.
32 Lieutenant Colonel Steve Hart, letter to the author, June 1993; RASCM, ‘A History of 547 Signal Troop in Vietnam’, pp. 25–30.
33 Murray, interview, August 1989. For a more detailed account on signals intelligence flights see Don Dennis, ‘Of Shush Missions, Voice Sorties and Pucker Factors’, in Australian Aviation, May 1991, pp. 39–41.
34 RASCM, ‘A History of 547 Signal Troop in Vietnam’, p. 6.
35 Murray interview, August 1989.
36 Murray, interview, August 1989. See also David Horner, SAS: Phantoms of the Jungle, Allen & Unwin, Sydney, 1990, pp. 255–60.
37 T.M. Rienzi, Vietnam Studies: Communications-Electronics 1962–1970, Department of the Army, Washington DC, 1972, pp. 170–1; and Murray, interview with author, August 1989.
38 Dennis in Australian Aviation, p. 39.
39 RASCM, ‘A History of 547 Signal Troop in Vietnam’, p. 24.
40 Ibid., p. 13; and Murray, interview, August 1989.
41 Whyte, interview, August 1989.
42 RASCM, ‘A History of 547 Signal Troop in Vietnam’, p. 17.
43 Murray, interview, August 1989.
44 Whyte interview, August 1989. In a similar concept, the artillery’s locating battery used a string of sensors to locate enemy guns. See David Horner, The Gunners: A History of Australian Artillery, Allen & Unwin, Sydney, 1995, p. 494.
45 RASCM, ‘A History of 547 Signal Troop in Vietnam’, p. 18.
