. Summary:
The were major problems at Barrow when the Astute contract was signed as over 20 years had passed since they built the last Vanguard - work force had dropped from 13,000 to 3,000 and most experienced people had retired. It took a lot of assistance from the US to get back up to speed again.
Once of the lessons learnt, as with aircraft, is that its essential to keep the design and manufacture teams intact and that is done by stretching out production between classes and boats to ensure the6 are always active.
In the case of Barrow the design team moved in from the Astute to Dreadnaught and are moving on in turn to SSNR. RR has completed the last PWR2B cores for Astute and has rebuilt their core production plant at Raynesway to build the PWR3 cores for Dreadnaught and SSNR.
At Barrow they are finishing off the last Astutes and stated work on the 3rd of the 4 Dreadnaughts (the construction hall can hold. 3 boats. The last Astute should be commissioned in 2026.
The first Astute was commissioned in 2010 with a planned 25 year life, so with current boats taking 8 years to be completed they should start work on the first SSN in the class just after the last Astute.
That doesn’t leave any space in the construction hall for any extra Astutes - or the reactors to power them. Planned SSNR construction will, presumably, be staged to replace the existing boats before they move onto the Dreadnaught replacement etc etc.
The assumption has to be, therefore, that SSNR construction for Australia will take place in Australia with RR providing the reactors from the UK and the UK and USA providing bith training and assistance, as the US did when the UK started Astute production.