Looking at the security aspects of the Nuclear Powered Submarine Taskforce’s subsite is interesting:
“The taskforce is a whole-of-government effort and is staffed with representatives from across government, including…the Australian Security Intelligence Organisation.” [ASIO]
Assisting ASIO in the vetting process of the Taskforce’s 250+ staff is the “Australian Government Security Vetting Agency”
The Submarine Taskforce staff would probably, or hopefully, already have Top Secret clearance for their pre-Taskforce jobs, To join the Taskforce they would probably require a more stringent clearance of TOP SECRET (SPECIAL ACCESS or CODEWORD). This may be the equivalent to the older clearance of TOP SECRET (ABSOLUTE) required of DIO staff.
Those on the Taskforce with a need to know of the US and UK Nuclear Reactor secrets would probably need to acquire US TOP SECRET (Q CLEARANCE [nuclear weapons and related materials]) which may require passing US Defense Counterintelligence and Security Agency polygraph tests.
To pass Top Secret (Special Access or Codeword) clearance in Australia requires“Negative Vetting Level 2 and Positive Vetting clearance holders can access classified resources up to and including TOP SECRET.”
In decades gone by I also had Top Secret Codeword clearance but mainly to do with highly compartmentalised special operations eg. see pages 156-159 and sigint operations.