It has not drawn much attention. But as 40th-birthday bashes go, it has been rather a spectacular affair. About 4,000 servicemen from five countries, 19 warships, 68 military aircraft and two submarines have been taking part in exercises in South-East Asia to mark the anniversary of the conclusion on November 1, 1971 of the "Five Power Defence Arrangements" (FPDA).

And the five defence ministers — from Australia, Britain, Malaysia, New Zealand and Singapore — convened in Malaysia and Singapore to give the occasion a high-level gloss.

You might imagine that they would be discussing an overdue retirement for arrangements made for an entirely different world. The security threats perceived in 1971 have evaporated. British colonial rule, which had come to an end just a few years before, is now ancient history to most Singaporeans and Malaysians, born since independence. For them the idea of looking to the British, Australian and New Zealand armies for security must seem bizarre. Meanwhile, regional co-operation has spawned a plethora of new security forums and organisations.

Yet the FPDA survive, and show no signs of packing up. Indeed, sheer longevity has in some ways strengthened them. They remain, in a phrase coined in Australia's defence ministry, South-East Asia's only "multilateral security arrangement with an operational dimension". Their durability is testimony both to the flexibility of the armed forces that have looked after them, and to a continued nervousness about the region's security.

The FPDA were a response to Britain's precipitate withdrawal of its forces from ‘East of Suez', which caused deep anger and resentment in the other four countries. They are far from a full-fledged military alliance. They provide merely for the five countries to ‘consult' in the event of an attack on Singapore and Peninsular Malaysia (Sabah and Sarawak, the Malaysian states on Borneo, are excluded). This gave Singapore and Malaysia breathing space to build up their own armed forces, while under some protection from British air defences.

The real danger was seen as Indonesia, which until recently had been eyeing Malaysia and Singapore as bits of its territory lopped off by an accident of colonial history. Among other worries, the Philippines had not dropped a claim to Sabah. And, of course, the Vietnam war was raging, raising fears of South-East Asian dominoes toppling to Soviet-aligned communism. Malaysia's and Thailand's armed communists have long given up the ghost. Indonesia and the Philippines have for over 40 years been joined with Malaysia and Singapore in the Association of South-East Asian Nations (Asean), and have stopped pursuing irredentist claims. Even Vietnam, the first domino in the queue, has been part of the family since 1995. And Britain's weight in the world has dwindled, as have its defence budgets. Even before its latest defence review outlined painful cuts, and despite the war in Afghanistan, Britain's defence expenditure, as a proportion of GDP, was less than half what it was in 1971.

Diversified operations

So the FPDA's survival seems puzzling. Partly, put it down to inertia — no compelling reason to terminate them. But also all five powers gain different benefits from them. Britain keeps a toehold in South-East Asia. New Zealand and Australia, which has made the biggest commitment of the ‘travelling' powers, see their own security as bound up with that of the region. Singapore and Malaysia acquire expertise and training from the other armies.

The FPDA has also deftly diversified. The ministers now discuss piracy, cybersecurity and humanitarian and disaster-relief operations. And the pact provides a mild sort of reassurance against other forms of instability. In the late 1990s that again meant Indonesia, in turmoil after the end of the Suharto dictatorship, sparking fears of disintegration and mass flight. Now, though it is a fear that dares not speak its name, it means China, and the assertive posture it has adopted in recent years towards disputed territorial claims, such as in the South China Sea. As Philip Hammond, Britain's defence minister, put it recently, a possible threat to regional security is a "miscalculation over a territorial claim, probably over an island somewhere". Another area of possible miscalculation might be the Malacca Strait, through which most of China's oil passes.

Tim Huxley, in Singapore for the International Institute of Strategic Studies, a British think-tank, points out that there is no way the FPDA can be part of ‘a balancing mechanism' to China, or that it will come into play in the South China Sea. Of the five, only Malaysia has a direct stake there.

The bewildering array of regional security talking-shops has so far failed to still such worries. Most hopes now are vested in a grouping known, with Asia's flair for alphabetical nomenclature, as the ADMM+ (for Asean Defence Ministers' Meeting). It groups Asean with America, China, India, Japan, Russia and South Korea, as well as Australia and New Zealand. One day, it might become a forum for settling disputes. Today it is barely even one for airing them. And in that context, the FPDA provides members with a vague sense of comfort that is also hard to pin down, and certainly less easy to explain than the premise of their 40th-anniversary exercises: the seizure of an island by a hostile power.