Escort building and ASW readiness

Would hundreds of early German U-boats have beaten British crash-built escorts because depth charges and prewar sonar were too weak?

Probably not. The visible buildup would have prompted more escort construction, testing, and earlier funding for weapons already under development, while depth charges were more than mere harassment.

A larger visible German submarine program would have changed British procurement and trials before 1939. Britain could answer with mass orders for sloops or corvettes while pushing ASDIC, Hedgehog, and related weapons through more active testing. Depth charges had real killing power, although early escorts remained less capable than their late-war successors. The answer does not claim that every improvement would be ready by September 1939, but suggests that some could arrive in 1940 or 1941.