Prime ministers cut down in their first term are thoroughly entitled to bear emotional and psychological scars — anger, remorse, revenge, regret and, of course, a sense of betrayal are understandable wounds to heal.

Odd, then, that of all the missteps Tony Abbott has had time to reflect on since his ousting in 2015, the one he now nominates as "probably the biggest regret I have from my time as PM" is one for which he has attracted almost no public criticism.

Mr Abbott is now repenting for his self-recognised failure of "not more robustly challenging the nuclear 'no-go' mindset".

In an 18-minute mea culpa speech on submarines, the former prime minister laid out what he describes as his "fears" for the $50-billion French submarine program locked in at the end of the Competitive Evaluation Process his Government had ordered.

"We've based our proposed sub on an existing design, but one that will need to be so extensively reworked that it's effective a brand new submarine," he fretted.

He likened the conversion of the French nuclear Barracuda submarine to a conventional diesel-electric boat as "the naval version of putting a four-cylinder engine into an eight-cylinder car".

"The resulting sub will have less power, less range, less speed and less capability than the existing submarine on which it is based," he said.

Australia's proposed sub would have been somewhat similar to this US one that was operating in a test with South Korea. ( AAP: YONHAP )

Mr Abbott concedes his personal preference of buying the Japanese Soryu class submarine was not the right answer either, because "we may have overestimated Japan's capacity to mount a bid and expected more than was reasonable of a submarine partnership virtually starting from scratch".

This is a considerable backdown from the opinion he held and expressed early last year that Japan had "the world's best large conventional submarine specifically designed to match the nuclear submarines of other nations".

Abbott plan would get 'fair hearing' under Labor

In challenging the "nuclear 'no-go' mindset", Mr Abbott is now advancing a radical alternative defence policy which successive Australian governments — including his own — have considered so complex, costly and politically controversial it has never been subject to serious examination.

Undaunted and acknowledging that he is "not a defence expert", only a "senior politician" with an "acute interest if not a profound expertise" in submarines, the Member for Warringah said Australia could develop a nuclear servicing industry from scratch within about 15 years — roughly the same time it will take to put the first conventional French submarine into service.

Mr Abbott remains optimistic that his plan could work, even if it is under a Bill Shorten-led Government. ( AAP: Dan Himbrechts )

According to the Abbott plan, this would entail a domestic capability based in Adelaide to maintain the reactors and fuel rods at the core of what would likely be American-designed nuclear subs.

Because the idea is so novel, the proposition is entirely untested on the notoriously fickle South Australian voter population, which has had no hesitation demanding the lion's share of an almost $200-billion naval ship building plan — but only on the understanding every vessel built would run on diesel fuel.

Still, the eternally optimistic former PM believes the idea is quite saleable — if not to his own side of politics, then to Bill Shorten.

"I am confident that at least under the present Labor leadership, it would get a fair hearing," he said.

Abbott confident public would back plan

As for the public, his assessment is "if it's clear to them we're not talking about nuclear weapons, we're talking about nuclear propulsion" and that if it can be presented as a matter of safety for Navy sailors sent to fight, then "the public would start to think 'maybe this isn't such a bad idea'".

Mr Abbott will find ready-made support among defence-thinkers who already fear Australia is embarking on a defence industry folly of unprecedented magnitude.

But politically he is waging a one-man war against settled bipartisan thinking and — as he was soon reminded by his colleague, Defence Minister Marise Payne — against his own once stridently held views on Australia's maritime defence needed through the first half of this Asian century.

Defence Minister Marise Payne (second from left) at the launch of a naval shipbuilding plan in Adelaide. ( ABC News: Nick Harmsen )

In a statement, Senator Payne said going nuclear would blow out the current timeframe.

"Australia currently lacks the qualified personnel, experience, infrastructure, training facilities and regulatory systems required to design, construct, operate and maintain a fleet of nuclear-powered submarines," she said in a statement.

"Developing this capability domestically would take far longer than a decade.

"The advantages of acquiring nuclear-powered submarines would be lost without the capacity to sustain them in Australia.

"Developing a sovereign nuclear-submarine fleet would also come at a very substantial cost premium to our conventional fleet."