The class carried the cruiser-submarine concept to its fullest wartime form. Its intended ability to reach American Atlantic ports made global deployment central to the design. Its purpose resembled that of a modern attack submarine carrying a small number of land-attack missiles more than that of a miniature aircraft carrier. Independent worldwide operation demands enough tonnage for fuel, stores, endurance, and useful weapons, even when the platform is not meant for a stand-up fight.
Chapter · 7:28-9:42
The I-400 as the ultimate cruiser submarine
The I-400 extended the cruiser-submarine idea into a globally deployable independent strike boat, with displacement buying reach and self-sufficiency.