If Japan had world-leading anti-submarine warfare

What if Japan had the world's best anti-submarine capability in 1940?

US submarines would suffer badly at first, but American intelligence and engineering would drive quieter, faster boats and new tactics.

World-leading Japanese anti-submarine capability in 1940 would make the opening of the American submarine campaign much more costly. Existing American torpedo faults would compound the problem. The projected response is to study operational intelligence about the Germans and use it to develop American boats. Higher underwater speed and anechoic tiles are suggested avenues. The timing and effectiveness remain hypothetical, but the central expectation is adaptation after heavy early losses.