Why submarine numbers mattered only if they arrived in time

Would receiving the Royal Navy's projected large submarine totals have transformed the war?

Only if the boats arrived early: a large force available in 1939, especially U-class boats in the Mediterranean, would matter far more than the same total completed by 1945.

The delivery date decides whether the Royal Navy's projected submarine totals matter. Boats arriving by 1945 would be too late to alter campaigns already decided. If they appeared in 1939, Britain could send many more theatre-suited submarines into action from the start. Roughly forty-nine U-class boats in the Mediterranean would threaten Italian naval forces and their supply routes to North Africa. The counterfactual shows why a planned total is different from useful wartime capability: the boats must exist in time and fit the waters where they are sent.