GUPPY submarines arrive twenty years early

What impact would GUPPY-modernized American submarines have if available during the Second World War?

The predicted advantage is overwhelming, although its size depends on the GUPPY version and whether the scenario includes postwar torpedoes.

Introducing GUPPY upgrades during the Second World War would give American submarines much higher submerged transit speeds and make rapid movement between operating areas easier. The precise advantage depends on the modernization standard: snorkels and directional sonar vary by version, while postwar torpedoes are an additional possibility. Working torpedoes alone remove a major limitation assumed in the wartime comparison. The predicted result is an overwhelming advantage against Axis naval forces, with an estimate of roughly six months to settle the naval war. GUPPY III brings technology associated here with 1961-1963 into a war fought about twenty years earlier.