Bradley Perrett | The AUKUS nuclear submarine plan has plenty of risk

We need those American subs to begin the build-up of our nuclear-propelled fleet. These are dangerous times, our diesel submarines will be inadequate in the 2030s, and we can hardly accept delays.

But the US doesn't have enough submarines for itself and could easily run into situations that heighten its needs. And if the US turned isolationist under a returned president Donald Trump, its willingness to make sacrifices for allies would diminish.

Our plan is first to get two second-hand Virginia-class subs from the US fleet, one in 2033 and one in 2036, then a new one straight from a US shipbuilder in 2039. For the moment, let's not consider the two extra Virginias that we'd ask for if the follow-on Anglo-Australian program to deliver SSN AUKUS submarines began running late.

Congressional approval is needed for us to get the first three. Encouragingly, the US Senate foreign relations committee last week gave its nod. The proposed legislation still needs to get through the full Senate and the House of Representatives, but there is clearly a lot of bipartisan support for Australia and the AUKUS partnership that's behind the plan.

Actually, it's a little surprising that things are going so smoothly so far.

"There's been a lot of talk about, well, the Australians would just buy a US submarine," Rob Wittman, then the top Republican on a House of Representative seapower sub-committee, said in December. "That's not going to happen."

"I just don't see how we're going to build a submarine and sell it to Australia during that time."

There's the snag. The US Navy says it won't build replacements for subs transferred to us until the 2030s, meaning beginning to construct them then. But, to synchronise the process and keep its fleet size stable, it would have to begin building at least one of the replacements in the 2020s.

It won't because it can't. The two shipyards that construct US submarines are not keeping up with orders running at two Virginias a year. They and their suppliers don't have enough skilled people. Two years ago the Pentagon quoted a US$1.5-2 billion cost to lift capacity to three Virginias a year, but more than that is being spent just to get the building rate up to two.

We're helping. Under AUKUS, we're paying $3 billion to increase the capacity of US and British submarine industries so they can also supply us; most of that money will go to the Americans. Also, in the next few years we'll send workers into the US industry and start making components here to help feed the American yards (and, along the way, learn something of the business of producing nuclear submarines).

Despite all that, the US Navy's planning reveals that the ramp-up will be slow, even if nothing goes wrong. The transfer of the first Virginia to us, and quite possibly the second, will temporarily reduce the US fleet.

The US Navy has said it needs 66 nuclear attack submarines, the specific sort we're discussing here. But it has only 49.

It's struggling to maintain even that number because old subs constructed in a gusher late in the Cold War are wearing out faster than new ones are arriving. To cover the gap, it's overhauling old boats to run them for longer than they were designed for.

The fleet is due to go even lower, to 46 in 2030. Then its crawl out of that valley will have barely begun when, under AUKUS planning, it will have to hand over a precious Virginia to Australia and wait years for a replacement.

The expected US legislation authorising the transfer will be great to see this year, but what about the risk of it being reversed later?

Reasons for the US Navy to turn around and beg Congress to let it keep all its Virginias are easy to imagine. If it's running overage subs, unexpected breakdowns are more likely. Accidents happen - even prangs. A US submarine ran into an underwater mountain in 2021 and is taking at least five years to fix. In 2012 a young shipyard worker who wanted to knock off early lit a fire in a sub he was helping to repair. It was a write off (and he got 17 years).

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Above all, the risk of war with China could become acute. If it did, the US Navy would urgently want every nuclear submarine it could lay its hands on. Hard to detect, they are the most valuable vessels for facing China.

We could argue that transferring submarines to us does not weaken the total strength of the alliance. But Washington could not be sure we'd help it in a war, and, anyway, it would regard nuclear submarines in newbie Australian hands as less useful than those with the US Navy.

Then there's Trump. Whether he would stay the course in resisting China in a second presidential term cannot be certain. Early in his 2017-20 presidency he was no China hawk, though he took a strong stand against Beijing later. His supporters are often contradictions, wanting to see an assertive US but also wanting it to get out of foreign troubles.

A new Trump presidency is in fact a massive but largely ignored issue for our defence policy in general. It's a risk for the nuclear submarine program in particular.