British planners would not build escorts only for a future German war; they also had to consider large submarines in French, Italian, Japanese, and possibly Dutch hands. British anxiety about French political instability intensified after the Spanish Civil War, making even a nominally friendly fleet part of contingency planning. A procurement rhythm sustained since 1930 might produce roughly 120 modern sloops alongside a similar number of destroyers. Those ships and trained crews would be available from the opening of war, with additional minelayers adding another source of early submarine losses.
Chapter · 45:51-48:08
Foreign cruiser submarines sustain a much larger British escort fleet
Concern about French, Italian, Japanese, and Dutch large submarines could leave Britain with roughly as many modern sloops as destroyers by 1939.