In October 1958, the British Chiefs of Staff proposed to hold inter-service exercises to identify vulnerabilities in the defence of the British Commonwealth. The following year, the Royal Air Force (RAF) sponsored the first of them, ‘Triumvirate’, in 1961, which planned for a hypothetical conflict in the Far East. Because Australia and New Zealand were especially vital to British plans, the UK Chiefs of Staff hoped that the combined services of those countries would send representatives to the top-secret ‘Closed Exercise’.

Defence officials in both Australia and New Zealand expressed doubts. Surely the (uninvited) United States would be ‘a most important, if not a preponderant power in these operations’. Australia’s Ministry of Defence registered concern that the exercise would slow progress on their efforts to establish ‘Four Power Planning’ in the Pacific with the United States – a project Australia and New Zealand called ‘Hydration’.

For Australia and New Zealand, Hydration offered the prospect of synchronising defence planning and potentially developing joint forces in Southeast Asia and the Southwest Pacific. In a global war, Britain was devoted to defending its Commonwealth and committed to reinforcing the North Atlantic Treaty Organization (NATO). Yet the Southeast Asia Treaty Organisation (SEATO), of which Australia and New Zealand were members, lacked an equivalent to NATO’s Article V, which committed members to collective defence. Accordingly, they sought to find another, more reliable way of tying the US into their defence architecture in the Pacific region.

US planners on the Joint Chiefs of Staff and Pacific Command did not wish, however, to be pinned down by commitments that would constrain America’s freedom of action. ‘Flexible realism’ – a term that appears in the November 2025 National Security Strategy of the United States of America (NSS) and the January 2026 National Defense Strategy (NDS) – sounds a lot like Washington’s approach to the world in the late 1950s. The lead-up to Triumvirate – an otherwise routine exercise – reveals much about cross-cutting dynamics shaping the Anglo countries with interests in the Far East. Moreover, it speaks directly to the US approach to that region and how it differed from Western Europe.

During the 1950s, the United States established a hub-and-spokes alliance system in East Asia – a ‘powerplay’, as Victor Cha calls it – that was designed not only to defend but also constrain allies. This system was established by signing bilateral mutual defence treaties with the Philippines in 1951, the Republic of Korea in 1953, the Republic of China in 1954, and a security treaty with Japan in 1951. In the Australia-New Zealand-United States Security Treaty of 1951 (ANZUS), Washington agreed to consult and coordinate during a crisis. Throughout the rest of the decade, Canberra and Wellington sought to determine what that meant.

As drafted by the Joint Planning Committee of the UK Air Ministry in October 1958, the wartime scenario for Triumvirate envisioned that, by 1961, governments throughout the Far East would be besieged by foreign communist subversion. A conflagration spreads in Laos, South Vietnam, and Thailand, and SEATO successfully repels the insurgencies. Fearing the collapse of the global Communist movement, the People’s Republic of China covertly infiltrates ‘volunteer’ forces. Determining that Beijing has crossed a red line, SEATO demands the immediate withdrawal of Chinese troops under the threat of nuclear attack on China’s mainland. Triumvirate ends with the United Kingdom and the (non-participant) United States moving their nuclear forces to high alert.

The Defence Ministry in Canberra doubted Triumvirate’s ‘military realism’ – particularly the ‘proposed division of responsibility between the British Commonwealth and the United States’. Moreover, not inviting Washington to send observers to the exercise might ‘revive her old prejudices against ANZAM (an evolving Commonwealth defence plan encompassing Australia, New Zealand, and British-ruled Malaya)’. And while the UK had given ‘adequate safeguards against Malaya and Pakistan becoming aware of the exercise’, the Australians felt that a ‘UK/A/NZ meeting would seem unlikely to escape [their] attention’.

In their own critique of the scenario, the New Zealand Chiefs of Staff concurred. Pakistan and Malaya might detect a Commonwealth ‘white man’s club’ within SEATO, in contrast to ‘keeping with the spirit of an international alliance’. Non-participating Commonwealth countries would also learn about their exclusion from the exercise.

It is hard to know how much Canberra or Wellington ultimately cared about that. Their overriding objective was to bind the Americans to the region. To them, the postwar security framework of the British Commonwealth was necessary but not sufficient. The fall of Singapore to the Japanese in 1942 had eroded the confidence of Australians and New Zealanders in the ability of Britain to protect its empire. According to Triumvirate’s scenario, SEATO would have faltered against Chinese intervention, short of Washington’s willingness to go nuclear.

Not all SEATO countries could be ‘read in’ to the programmes required by Triumvirate. Yet Australia and New Zealand benefited from intelligence sharing, which attracted the Americans. Canberra and Wellington participated in both the British-led Commonwealth Signal Intelligence Organisation and the March 1946 British-US Communication Intelligence Agreement (BRUSA) – later known as the United Kingdom-United States of America Agreement (UKUSA) – which included them after May 1955. It was not outlandish to build on this unique relationship to coordinate defence planning for the Pacific.

At the start of 1958, London was supportive. In February, British Prime Minister Harold Macmillan broached the prospect of four-power planning with Australian Prime Minister Robert Gordon Menzies. The potential for Canberra was to establish a ‘need to know’, and gain insights into ‘American capacities, particularly in the atomic field’, and ‘whether American available forces and weapons were such that it was inevitable that any war in the Far East would involve a nuclear war’. The British were probably interested in the same questions.

On 18 April 1958, Macmillan wrote to Eisenhower to propose four-power talks. SEATO could not be such a forum; its members could not reliably keep military secrets. Macmillan acknowledged that ‘forming an inner circle of SEATO Powers’ (to exclude the Philippines, Thailand, and Pakistan) would cripple an organisation meant to ward off communist penetration.

Indeed, discussions about the ongoing saga in Indonesia – where insurgents threatened the enigmatic President Sukarno’s hold on power — suggested that the Anglophone countries were doing just that. Eisenhower responded favourably to Macmillan on 24 April. The president suggested that the British Ambassador, Harold Caccia, meet with Secretary of State John Foster Dulles. Caccia and Dulles had recently gathered to assess the strength of the rebels in Indonesia. Dulles confided in Caccia that covert action alone would not succeed in Indonesia and that the United States would also need to deploy military force.

The best-case scenario was to find a political basis for overt support – ‘rather than get caught covert’, as Dulles put it on 15 April. Establishing a ‘political basis’ for overt intervention might also overcome the reservations of New Zealand’s Prime Minister, Walter Nash.

On 14 April, the Australian Ambassador to the United States, Howard Beale, told Secretary of State Dulles that ‘according to Australian intelligence, the dissidents are disunited and are not likely to make a successful stand’. Dulles concurred. Calling in Britain’s Ambassador to the United States, Sir Leslie Munro, on 18 April (the same day as Macmillan’s letter to Eisenhower), Assistant Secretary for Far Eastern Affairs Walter Robertson insisted ‘the US is not considering going into Indonesia with force’ and that ‘he agreed with Prime Minister Nash that nothing could be more catastrophic than our going in with force’. To the blunt question of whether the US had ‘written off the rebels’, Robertson prevaricated.

As the Sumatra rebellion fizzled over the next few weeks, Dulles made clear that no rationale had emerged for overt involvement. In a meeting with the British Foreign Minister Selwyn Lloyd on 4 May, the secretary of state ‘observed that he did not see any possibility [of open intervention] which would not have the most disastrous consequences for us throughout the Far East’.

Four days later, an anti-aircraft battery downed CIA pilot Allen Pope over Indonesia’s Ambon Island. Pope survived, but the ensuing diplomatic crisis led the Dulles brothers to end covert operations.

Against this backdrop of failure, the US and UK proceeded gingerly on four-power planning. The British Commander-in-Chief of the Far East Land Forces, General Francis Festing, met the US Commander in Chief, Pacific Command (CINCPAC) Admiral Felix Stump in early May in Pearl Harbor for ‘informal military planning talks’. When Eisenhower and Macmillan next met in person, in Washington on 9 June, Ike reiterated: ‘the main question is how to get Australia and New Zealand included’, to which the prime minister responded: ‘both countries are happy to have the UK open discussions on this subject on their behalf’.

On 20 June, UK Ambassador Caccia and Head of the British Joint Staff Mission Admiral Michael Denny met in Washington with Assistant Secretary Robertson, Department of State Counselor George Reinhardt, and Chief of Naval Operations Arleigh Burke and Admiral Stump, who ‘happened to be in town’. In their discussions, the British and Americans ruled out Bangkok and Singapore as sites for joint planning – the risk of exposure was deemed to be too great, as the negotiations ‘must be kept absolutely secret’ — and settled on Pearl Harbor instead.

On 27 June, Lord Hood of the British Embassy provided Marshall Green of the State Department’s Far East Bureau with a revised draft of a joint directive, along with oral instructions that the British wished to exclude Hong Kong from the directive; safeguard their freedom to act ‘collectively or individually’ to protect British and Commonwealth interests throughout Southeast Asia; and ‘discuss exclusively with the US the question of coordination of nuclear contributions in the Far East, including combined target studies’.

Hovering over these discussions was the long-term prospect of the People’s Republic of China’s nuclear ambitions. Australian defence officials wanted to know the likelihood of China obtaining a ‘nuclear capability within the next ten years’ and the feasibility of certain SEATO concepts. One such idea was that SEATO forces would ‘carry out air attacks on North Vietnam (the Chinese mainland and Hainan Island) using nuclear and conventional weapons as soon as aggression by the Vietminh (and the Chinese Communists, respectively) is detected’.

There was also the near-term prospect of a war over Taiwan. ‘The most serious gap of all is lack of knowledge of American capacities’, Menzies wrote Macmillan on 5 June. ‘Of the political differences in the region, I imagine that the one most likely to present problems for military planning will be the extent to which any of us is ready to regard an attack by Communist China on Formosa [Taiwan] as an act of aggression calling for joint resistance.’ Such concerns proliferated when, that summer, the People’s Republic of China shelled Quemoy and Matsu, threatening to reignite the Chinese Civil War.

‘It may be that the best Americans will agree to will be bilateral United Kingdom/United States talks’, Canberra messaged the Australian Embassy in Washington on 20 June. ‘In that case, we would have to rely on our ANZUS association and on our own special relations with the United Kingdom to keep in the picture and be able to express our views. It will be our objective to get an arrangement which includes Australia.’

Nurturing firmer US-UK military planning in the Far East, in other words, was a fallback option. That would be better than nothing.

Throughout the summer of 1958, Australia, New Zealand and the UK sought to finalise a venue and date for a meeting with US counterparts. Prime Minister Nash was reluctant; it ‘seemed to him that what was emerging was not Four Power Planning but the United States telling the other three countries what they could do to assist the United States’ plans’. Nash’s suspicion had merit.

Meanwhile, Washington and London were coordinating in ways neither Canberra nor Wellington could have known. On 3 July, US Deputy Under Secretary of State Robert Murphy and UK Deputy Under-Secretary at the Foreign Office Sir Patrick Dean signed the landmark US-UK Mutual Defence Agreement, which allowed the sharing of classified nuclear information between the two countries and established procedures for joint decisions on the use of nuclear weapons. Codifying the ‘Special Relationship’, Washington and London created their own circle within the Anglosphere. In the nuclear denouement of the Triumvirate scenario, London must have known more about ‘military realism’ than they confided to Canberra and Wellington.

Also in July, Admiral Harry Felt replaced Felix Stump as Commander of US Forces, Pacific Command. A September cable from CINCPAC to the Pentagon spelled out the agenda for a Four-Power Planning Conference to be held in Hawaii from 1-7 October. The conference coincided with the 6 October ceasefire with respect to Quemoy and Matsu – the negotiations of which must surely have taken up much of Admiral Felt’s attention.

‘During the discussions the American planners were co-operative and appeared keen to make the planning effective, and it was expected that the report of the meeting would follow the return of our delegation to Australia’, according to the official report by the Australian Defence Committee in March 1959. ‘Instead, after some delay, a signal was received from Admiral Felt stating that he had significant reservations on the draft report.’ In similar letters to the other military representatives, Felt expressed fears that such planning – by an ‘inner white ring’ – would come at the expense of SEATO. While true, this statement provided a convenient excuse for inaction.

The Australian report dovetailed with the impression of the British Defence Coordination Committee ‘that the real American objection to four-power planning is that they are reluctant to be committed to fight any war of a plan concerted with Allies either in or out of SEATO’. The British believed that ‘the Americans are unwilling to commit land forces in South East Asia’. The Australians concluded: ‘This is a question of the utmost importance in planning for the defence of South East Asia, but one on which it will be most difficult to establish an unequivocal United States attitude.’

Canberra and London had it right. Here and elsewhere, US equivocation was intentional. It is easy to view 1958-59 through the lens of America’s ill-fated Vietnam experience, though that future was as yet unknown.

If anything, the exposure of the CIA’s involvement in Indonesia suggested that the Americans might be on the way out. In a private conversation in January 1959 at the Australian Commission in Singapore, the Head of the Far East Defence Secretariat, Colonel D.S. Humphrys, said that ‘the Americans were confident that they had the military resources to take care of any situation that might arise in this part of the world’. Humphrys continued: ‘Now that a good deal of the heat had gone out of the Indonesian situation as compared with six months ago’, for the Americans, ‘the main raison d’être for Hydration no longer’ remained.’

The Far East Defence Secretariat concluded that with Indonesia no longer a ‘hot’ issue, the Americans were ‘reluctant to be drawn into any additional defence commitments, even to the extent that this was implied in joint planning, primarily because they were confident that they could provide the necessary hardware to deal with the Communist threat in the Far East from their own resources’.

Humphrys was correct in his assessment of the Eisenhower administration’s approach. His depiction of Hydration smacks of exasperation. Its raison d’être was responding to crises, of which Indonesia was merely one example.

It is easy to equate the motive with US intransigence. Yet the declassified records in the Foreign Relations of the United States series and elsewhere reveal that US policymakers bemoaned the multitude of challenges they faced and laboured to find clear solutions.

Consider the candour of John Foster Dulles on 1 October 1958, as he hosted Australian Foreign Minister Richard Casey and New Zealand Prime Minister Nash at the State Department under the auspices of ANZUS. Dulles had warned Chiang Kai-shek not to move so many forces to Quemoy and Matsu, yet the generalissimo had not listened. Still, he ruled out backing down.

‘If you could find any way to sink these islands into the sea, if you should have an earthquake come along and sink these islands to the bottom of the sea, it would be unfortunate because of 125,000 people on them, but leaving aside the human element, it would be an ideal solution’, as Dulles put it. ‘If there would be great earthquakes, then we would be better off. Then it would be done as an Act of God and not as an act of the United States.’

A few weeks after that meeting, Nikita Khrushchev demanded that the western powers withdraw from Berlin within six months, triggering the Second Berlin Crisis. Triumvirate presumed that the US would climb the ladder of nuclear escalation in the Far East, but would they do so even in Europe? Granular minutes of a National Security Council meeting held on 1 May 1958 show that Dulles himself did not believe the message he was conveying publicly: that Americans would equate a Soviet attack on Berlin with an attack on the American homeland.

Washington thus had understandable reasons to preserve its freedom of action in the Far East and elsewhere. Joint military planning brought with it the prospect of commitments it was not prepared to make – or, at least, obstacles it was unwilling to countenance.

Flexible realism made sense to US policymakers in the late 1950s. Ratcheting up the pressure during the Second Taiwan Straits Conflict appeared to have worked – the absence of coordinated four-power military planning notwithstanding. A showdown over Berlin loomed on the horizon. Ultimately, US and allied strength compelled Khrushchev to back down in the summer of 1961 and again in October 1962.

Formal alliances yielded benefits, yet required commitments to fight; informal ones were less costly. From Washington’s perspective in 1958, strength prevailed without the need for binding commitments. By our reading of the 2025 NSS and 2026 NDS, this logic corresponds with Washington’s current intentions. The declassified historical record after the Second World War suggests that, when done right, flexible realism led Washington to build an array of formal and informal alliances in the Far East, a large swath of today’s Indo-Pacific. Now, as then, prudent decisions will make or break strategies.

The views expressed here do not necessarily reflect those of the US Government.