Marine Engineer, Professor Jonathan Gates authoritative 188 page UK publication:
Astute Class Nuclear Submarine: 2010 to date (Haynes Owners' Workshop Manual, 2018).
On page 159 Gates indicates the most important missions of Astute submarines (and by extension SSNs generally):
"Astute class submarines have a major role in ensuring that SSBNs are not followed in peacetime and are protected in wartime.
They are also responsible for tracking enemy SSBNs and neutralising them in times of war."
All navies that have SSNs see their SSNs' major role as protecting their own nuclear missile armed SSBNs while being prepared to destroy enemy SSBNs.
1. So where does this leave Australia? Australia's intention is to acquire a large fleet of 8 SSNs for a "small-medium" power, while having no public plans to acquire SSBNs.
Or will Australia become an ally in nuclear war fighting...
2. Might the Australian Government's insistence that "Australia's AUKUS SSNs will be conventionally armed" disguise roles of protecting US SSBNs in wartime while destroying Chinese SSBNs in wartime?
3. Or something else?