Wreck of Monster IJN Submarine I-400 Found off Hawaii!

[Dread Knot]

Following the war, submarine experimentation and design changes would continue in this direction, eventually leading to ballistic missile launching capabilities

Actually, the German were already experimenting with launching missiles from submarines before this behemoth kissed water. Given the amount of time it would take to assemble it's plane for launching, the I-400 represents more of a dead-end in submarine development than a breakthrough.