Japanese mothership doctrine and the midget-submarine problem

Why was the 1930s Japanese Navy so interested in motherships and midget submarines for a decisive battle?

Motherships could multiply small striking units, but the Pearl Harbor midget-submarine plan added excessive complexity; long-range boats near US ports would have offered more leverage.

The Imperial Japanese Navy's interest in motherships followed its desire to concentrate numbers for a decisive battle. Japanese planners repeatedly used parent ships to carry smaller attack systems toward the expected engagement. The midget submarines sent to Pearl Harbor were an especially complicated application because their deployment and recovery added risk to an already demanding operation. A counterfactual alternative places capable long-range boats near American ports to attack forces reacting after Pearl Harbor. Multiplying units looked attractive in theory, but delivering them created a heavy operational burden.