Mr Beazley told Fairfax Media he was not arguing for the abandonment of the plan to acquire 12 new submarines, which was the centrepiece of the government's recently-released defence white paper.

But he said: "Technologies in the military sphere are about to change dramatically, and the comfort that we have with [contemporary capabilities] … could very well become an obsolete one, well short of the time limitation they have permitted themselves in the white paper."

Mr Beazley, a recent Ambassador to Washington, was speaking from Singapore where he was attending the Shangri-La regional defence summit. He said the key questions around defence equipment were "not so much will the money be there, but will the technologies be right … it's a warning flag [on the submarines] and just about everything else we do".

Australia's conventionally-powered submarines have proven almost impossible for the US military to detect in exercises but new unmanned undersea platforms could make for better detection and therefore greater vulnerability.

Mr Beazley was speaking in advance of the release of the Australian Strategic Policy Institute's Strategy: Agenda for Change 2016 document which outlines the major strategic challenges facing an incoming government after the July 2 election.

Writing in the forward to the ASPI document, he says "Artificial intelligence, autonomous systems, direct-energy weapons and applications of those changes in space and underwater systems …disturb not only our priorities but the viability and relevance of some very expensive [defence] platforms".

Elsewhere in the ASPI document, executive director Peter Jennings warns that Islamic State will "try to break the coalition's will by staging more terrorist attacks around the world" as it loses ground in Iraq. The Institute's head of counter-terrorism policy Jacinta Carroll sounds a similar warning, and calls on the next federal government to step up exercises in counter-terrorism.

She says the slow-moving Lindt Cafe inquest in Sydney has demonstrated that state coroners' processes are not best suited to "review operational effectiveness" in counter-terrorism incidents, and recommends that Defence examine how better to support the states in responses to terrorism.

Other analysts warn that slower economic growth in the United States could mean an increasing transfer of the "burden of keeping the peace to its allies and partners".

Defence budget specialist Mark Thomson says US presidential candidate Donald Trump's "truly bizarre brand of belligerent isolationism" may be an aberration but fits with "longer-term US demographic trends [which] will diminish the proportion of [US] voters who identify with the postwar generation that defined the country as the leader of the free world".

Mr Thomson also challenges government claims – made frequently so far during the election campaign – that local defence spending will significantly spur economic growth.

"On the scale of the 10-million strong Australian labor force, the promised 5500 or so [naval] shipbuilding jobs are a drop in the ocean," he argues. "Moreover, despite talk of 'high-tech manufacturing', much of the work will be routine fabrication. Critically, almost all of the key components and advance weapons systems for our future naval platforms will be imported."

On climate change, the institute warns that "the security agencies and the military view climate change as a 'threat multiplier', as the effects on food, water and health security could exacerbate existing tensions, increase social instability, drive large-scale migration and trigger violent conflict."

It says this will increase pressure on the Australian Defence Force to deliver assistance "more often and on a much greater scale".

Several analysts warn of the need to keep cyber-security to the fore of government planning, with head of international cyber policy Tobias Feakin arguing that "even modest methods of attack can lead to cascading failures in government, business and society."