It's the biggest defence deal in Australia's history.
 

Costing up to $368 billion, the AUKUS agreement with the United States and the United Kingdom is supposed to deliver Australia a fleet of the most advanced nuclear-powered submarines in the world.
 

But serious questions are being asked about whether Australia will ever get what it paid for — and now that the Trump administration has ordered a review into the deal, there is even more worry that the submarines we are banking on won't turn up.
 

We travelled to the corridors of power in Washington and London to speak to top defence and political figures about the AUKUS program, with some raising concerns about whether the US and the UK has the skilled workforce to deliver what they've promised.
 

As one former UK National Security Adviser told me, Australia should brace itself for bad news that the delivery of new UK-designed nuclear subs will be late and more expensive than planned.
 

Then there's the Trump effect. In the US, we spoke to senior political figures who fear that the US president could represent the biggest threat to AUKUS.
 

One high ranking member of the US House of Representatives Armed Services Committee told me that Trump's contempt for allies threatens not just the AUKUS deal, but the strong partnership between Canberra and Washington.
 

With so much at stake — billions of taxpayer dollars and Australia's entire Indo-Pacific defence strategy — Four Corners investigates whether AUKUS will succeed, or sink.
 

Watch Four Corners: Submerged, tonight from 8.30pm on ABC TV and ABC iview.