More Upholders could lead to a Commonwealth SSK

What might replace a larger Upholder fleet shared by Britain, Canada, and Australia?

The scenario could justify more British SSNs or, more likely, create the basis for a joint Commonwealth conventional-submarine programme.

The counterfactual begins with a Royal Navy that completed twelve Upholder-class submarines. If Britain retained four while Canada and Australia each received four, the shared fleet could sustain a common training, support, and replacement problem. Australia might still build the Collins class and operate it alongside the Upholders, but the overlap could alter that programme's path. Plausible successors include additional British SSNs or a joint Commonwealth SSK, with neither presented as inevitable.