How Britain prepared escorts before the U-boat war

Why did the Royal Navy not respond quickly enough to German submarine construction before the war?

It did begin multiple escort programs before war, but building enough ships took time and convoy defense required many more escorts than Germany needed submarines to exploit a weak point.

Britain had three prewar responses under way: Hunt-class escort destroyers, Flower-class corvettes, and conversion of V-and-W destroyers into long-range escorts. The problem was therefore not complete institutional surprise. Escort forces had to be present across entire convoy routes, while submarines could concentrate where coverage was thin. The historical record also overrepresents badly hit convoys because routine crossings attract less attention. The distinction separates a genuine numerical shortage from the claim that Britain had made no preparations.