North Korean midget submarines and their limited roles

Are North Korean midget submarines useful in naval combat, or only for special-forces infiltration?

They can support littoral defense and operations in confined waters as well as infiltration, but the level of investment described is questioned.

Midget submarines can support littoral defense, operations in confined waters, and special-forces insertion. Those uses extend beyond transporting infiltrators, but they do not by themselves justify the scale of investment described for North Korea. The assessment here questions that level of spending. A lack of practical alternatives is offered as a likely reason for continuing the program.