If the Mark 14 torpedo worked from the start

What if the US Navy had properly tested and fixed the Mark 14 torpedo before the Pacific War?

Japan suffers earlier warship and merchant losses, worsening later operations and logistics and probably shortening the war by several months.

Reliable torpedoes would allow more American submarines to survive early patrols and sink Japanese capital ships, carriers, and merchant vessels before later campaigns. At least two Kongo-class ships and perhaps a carrier could be lost by the end of 1941, though this is a counterfactual estimate rather than a firm prediction. Fewer heavy units would be available around Guadalcanal, while greater merchant losses would worsen Japanese logistics. That disruption could deepen Army-Navy disputes as supplies failed to reach their destinations. The cumulative effect could shorten the war by several months without producing a single decisive reversal.