[PGR88]

Wartime prime minister General Hideki Tōjō catalogued submarine warfare among three critical determinants of Japan's defeat—high praise from someone in a position to know.

The entire US Pacific submarine service in WWII had less than 16,000 total members. Talk about punching above one's weight and over-sized contribution!

[colorado tanker]

The fleet really threw a punch once the Navy got torpedoes that actually blew stuff up. The early torpedoes were terrible.

[RayChuang88]

Correct. US submarine forces during World War II effectively choked off Japan's supply of raw materials like minerals and oil, and that so degraded the Japanese military that if we had carried out Operation Downfall, the defense of the Japanese home islands would have not have lasted long other than a massive casualty toll among the Japanese defenders.

[Sparklite]

Additionally, the WWII silent service spent a good portion of the war firing useless torpedoes.

http://www.historynet.com/us-torpedo-troubles-during-world-war-ii.htm