Sen Toku - Mega Japanese submarines

In 1942, Japanese designed a master plan to attack the USA by using mega submarines, carrying planes and bio-weapons.

About the SenToku

Developed during 1943 and 1944, 3 of the submarines were ready in 1945 to strike San Francisco, Los Angeles and Panama. Thanks to the Japanese military inefficiencies, they changed the plans at the last minute.
They had stock of bubonic plague and were sailing to their objectives until the atomic bombing. They surrendered to US Navy in 1945.

Interestingly, they were all sunk in 1946 before anybody else than the US navy could examine them.