Britain expected cruisers to impose blockades and capture merchant ships, so German-style submarine commerce warfare was not the fleet's first priority. Royal Navy submarines instead acted as mobile minefields, waiting on likely routes to damage major units and break up task forces. A massed torpedo salvo did not need to sink every capital ship; a mission kill could send a damaged ship home with part of the destroyer screen. In Far Eastern plans, submarines worked with chokepoints, intelligence, and mines to create layered ambushes.
Chapter · 6:54-15:17
Why the Royal Navy built ambush submarines
The pre-war Royal Navy treated submarines as ambush weapons, scouts, and minelayers rather than its primary commerce-raiding arm.