Roughly twenty T-class submarines were operating across Royal Navy theaters at this point. That pool makes a Far Eastern reinforcement possible, but it does not mean all or even most could leave existing duties. American submarines would probably remain more numerous around Singapore, while many British boats already in the region were older types. The surviving base changes where submarines can operate more than it creates an unlimited supply of modern T-class boats.
Notable Point · 2:51:39-2:53:45
How many T-class submarines could reinforce Singapore?
Britain had roughly twenty T-class boats across all theaters, so only a subset could move east and older boats would still dominate locally.