More submarines require more escorts for ocean and coastal convoys, including protection for ports. A longer warning period gives Britain time to expand the infrastructure needed to build those ships. Dominions and some colonies could adapt British designs to their own production capabilities. Corvettes were already being ordered before war historically, and the projected continuation of preparations for a major war after 1942 would sustain large orders. Dedicated escorts preserve destroyers for fleet operations: using destroyers for convoy runs instead would reduce what the main fleet could do.
Notable Point · 1:08:53-1:14:41
Dedicated escorts free destroyers for fleet duties
A growing submarine threat makes corvettes and escorts essential, allowing a navy to protect trade routes without stripping destroyers from its battle force.