How an interwar sloop programme transforms convoy defense

How many sloops could Britain afford and crew before the Second World War?

Eight to twelve a year, potentially about 120 by 1939, with most reserve-manned until mobilization.

Sloops were inexpensive enough for Britain to continue ordering them without displacing its major-warship programme. A steady annual output of eight to twelve could accumulate around 120 vessels by the outbreak of war. Only a fraction would require full peacetime crews, while the remainder could sit in reserve for mobilization. With crews of roughly sixty and a large reserve system, the personnel burden was manageable, and the resulting escort mass could severely reduce the early submarine threat.