Black Swan sloops and the escort-carrier answer

How could Britain have countered a much larger prewar U-boat force before late-war ASW weapons became available?

With mass-produced sloops such as the Black Swans, earlier-funded small carriers, and tactics that forced slow pre-snorkel submarines underwater and away from convoy targets.

Early U-boats relied heavily on deck guns because torpedoes were expensive and limited, so strong escorts could deny their preferred surfaced attacks. Black Swan-class sloops could force a submarine underwater before it reached the merchant ships. A submerged Type VII or Type IX was too slow to chase a convoy and suffered a major patrol-range penalty. The Royal Navy's unfunded small-carrier ideas and HMS Unicorn also show how an earlier threat might have accelerated plans for carrier-based hunting groups.