The promise and limits of Japan's submarine arm

What is your assessment of the Imperial Japanese Navy's submarine arm?

It contained good ideas, but specialized concepts and weak operational application prevented it from realizing its potential.

Parts of Japanese submarine design and policy show real merit. Midget submarines were attractive as a way to attack ships protected inside a harbor, much as British X-craft later attacked Tirpitz. At Pearl Harbor, greater effort toward making the main aerial torpedo strike reliably effective would have offered more value. An ingenious specialized weapon still has to be judged against the wider operation and competing uses for its resources.