On stage for his “arsenal of freedom tour”, the US secretary of defense – who prefers the appellation “secretary of war” – was ebullient.

“This Virginia-class submarine is a paragon of American engineering and fighting spirit,” Pete Hegseth roared, standing at Newport News shipyards where those boats are being built. “It is the apex predator of the undersea domain, the most advanced and lethal submarine ever built.”There are few who would argue with the Virginia’s lethality. Australia is set to buy three of these boats, second-hand, from the US Navy, beginning in 2032. But is it the right submarine for Australia?

Hegesth’s words, for all of their rhetorical bellicosity, were revealing: “American … fighting spirit”; “apex predator”; “ensuring America is free and safe and powerful”.

Virginia-class submarines – nuclear-powered and conventionally armed – are very good at travelling undetected fast and staying underwater for a very long time (limited, essentially, only by the capacity of the crew to stay submerged).

They are an attack submarine, an outstanding offensive platform for hunting and destroying a far-distant adversary, able to traverse thousands of miles of deep ocean undetected.

But Australia’s National Defence Strategy released this year, says the nation’s “strategy of denial” – which aims to deter conflict before it begins – was “focused on safeguarding Australia’s interests in our primary area of military interest”. This includes the immediate region encompassing the north-east Indian Ocean through maritime Southeast Asia into the Pacific as well as Australia, its populated offshore territories and its northern approaches.

A growing chorus of naval experts is arguing that the Virginia-class submarines are the wrong boats for this country.

The waters to the north of the Australian continent – from where any potential threat is overwhelmingly likely to approach – are shallow, best suited to a submarine far smaller than Virginia’s nearly 8,000 tons of displacement, some say.

A smaller, more nimble submarine, quieter when operating under battery, is a better platform for that role, they say. In addition, smaller submarines are cheaper and easier to crew: Australia could afford more of them, increasing the potency of its force.

The argument runs thus: the Virginias, and the even larger Aukus-class submarines set to follow, are nuclear-powered submarines perfectly suited to fighting a distant war on behalf of the US. But they are the wrong boats to defend Australia. Defence or ‘projecting power’?

Dr Andrew Gaczol spent a decade as an international political analyst and policy officer at the Australian department of defence. He told an independent inquiry into Aukus coordinated by the Australian Peace and Security Forum that the Australian public had been provided only two arguments in support of the Aukus deal, “and neither stand up to serious scrutiny”. The primary argument put forward is that of defence of Australia.

Gaczol told the inquiry it was unnecessary to have submarines with unlimited range to defend the nation’s waters or conduct defensive operations in the region.

“The latest state-of-the-art Air Independent Propulsion (AIP) conventional diesel-electric submarines are more suitable as they are smaller, quieter when submerged and better suited to the relatively shallow waters of the Australian continental shelf and the waters to Australia’s north,” he said.

The second argument propounded for Aukus is the need for Australia – as a nation reliant on trade – to maintain open sea lanes around it.

Given the small number of attack submarines the Aukus deal will ultimately provide, critics argue they will not be able to protect Australia’s seaborne approaches.

Navies around the world operate on “the rule of threes”, which states that for every three of a complex platform you possess, only one can be relied upon to be operational at any given time. Essentially, of three submarines, one is on active deployment, one is training or conducting exercises, and one is in maintenance, dry dock or recovering from operations.

Australia plans to buy three Virginia-class submarines from the US, to be supplemented – when they are designed and built – by up to five submarines of the Aukus class. By the end of the 2040s, eight submarines would give Australia, at any time, a fleet of two, perhaps three submarines on active deployment.

“I can’t see how such a small number of vessels will be able to keep open all of Australia’s trade routes all of the time,” Gaczol told the inquiry.

“As a counterpoint, I note that the US Navy has over 60 nuclear submarines and are currently unable to force open the strait of Hormuz.”Gaczol says he supports Australia having submarines, but that the Virginia and Aukus-class boats were not ideal for Australia’s defence. The benefit of Australia’s geography – a vast landmass protected by thousands of kilometres of ocean – mean “the chances of Australia being actually sort of invaded are virtually nil”.

The oceans to Australia’s north are also relatively shallow – under 200 metres deep across parts of the Indonesian archipelago and South China Sea – meaning large nuclear submarines “are more easily detected” than smaller and quieter conventional boats.

As deep-water boats that can travel anywhere around the globe at high speed, nuclear submarines are unnecessary for defending Australia, Gaczol says, and are instead about “projecting power into another part of the world”.

“To put it colloquially, that’s not protecting our patch. That’s going into someone else’s patch and poking them in the eye,” he says.

Gaczol believes the acquisition of Virginia-class submarines suits US imperatives, not Australia’s.

“The only scenario I can really see these boats being applicable for is to chase Chinese submarines in the South China Sea should it come to a conflict there. Effectively, our force will be an adjunct of the US Navy.”‘Best deal on offer’

Former South Australian senator Rex Patrick, an ex-submariner and resolute Aukus critic, is familiar with the aphorism “quantity is a quality of its own”.

He says while there was undoubted advantage to buying large attack submarines – greater payloads, more torpedoes, more capability to transport special forces soldiers – “there’s always a trade off”.

“If the cost of buying one large nuclear submarine is that you could buy four other submarines for the same price, that’s a trade off you have to consider.”Aukus is forecast to cost up to $368bn by the 2050s – $33m a day for 30 years on a conservative estimate. Few, if any, major defence projects of this complexity run on time, or on budget.

And Aukus is dependent not only on Australia’s efforts to build a nuclear-powered submarine fleet from scratch: it is reliant on the US – beset by tenaciously laggard boat-building –to construct enough Virginia class boats to spare three for Australia and it needs the UK’s sole submarine-building yard to design and build the first of the new Aukus class boats, on which Australia’s domestically built boat will be constructed.

For far less than the slated cost of the Aukus deal, Australia could buy 20 conventionally powered air independent propulsion submarines, Patrick says.

“If you had 20 submarines, you’d have seven boats in the water, in seven different locations, and seven times the magnitude of problem for the other commander,” he says.

Patrick notes Canada, with the longest coastline in the world and facing many of the same geopolitical challenges as Australia, recently announced it would buy 12 air independent propulsion submarines from German shipbuilder TKMS for a reported $33bn.

The Australian government, though, insists Aukus is “the best deal on offer”.

In June, the defence minister, Richard Marles, told the Shangri-La dialogue Australia had made the deliberate choice to increase the weight of its naval spending: more than 40% of Australia’s defence budget is now directed towards the country’s maritime domain.

“For a three-ocean nation, this is a strategic necessity,” Marles said. “Ninety-eight percent of Australia’s traded goods passes through Australian ports. Ninety percent of our fuel is imported. Our economic sovereignty, in the most basic sense, is a maritime proposition.”And Marles argued an increasingly militarised region demanded a collective response.

“The free and open passage of goods, energy and data across the seas is not just Australia’s economic lifeblood – it is the economic lifeblood of this entire region.”In a Lowy essay former special envoy for defence Luke Gosling wrote that nuclear submarines will give the Australian Defence Force “a regionally superior capability that will help it to deter war and, if it must fight a war, to win”.

“Threatening to aggressors, lethal if provoked, but not overtly provocative, nuclear submarines are the ‘goldilocks’ long-distance capability.”Amid a rising drumbeat of concern over Aukus, Labor Senator Raff Ciccone rose in the senate in June to argue Australia’s strategic environment had changed dramatically and the country “must respond to the world as it is“Nuclear powered submarines are the only platforms that can provide Australia with the ability to deter threats to our maritime supply chains, on which our way of life depend,” he said. “They alone have the speed, the endurance and the stealth necessary to effectively provide this deterrence. They are the bolt cutters that will ensure that we are never wrapped in chains.”