Historically, the boats were pulled back over 1940 and 1941 as Mediterranean demand and losses grew, rather than recalled in one move when war began. Without that pressure, more T-class submarines can remain in the Far East and later boats may join them. Their initial role is deterrence and a force in being. Because they can return through the Suez Canal to reinforce Alexandria, the deployment preserves strategic flexibility if a European war opens later.
Notable Point · 3:05:17-3:06:26
Why more T-class submarines remain in the Far East
Britain's T-class submarine withdrawal was gradual and driven by Mediterranean losses, so a war delayed beyond 1939 leaves more of the force in Asia as a deterrent and reserve.