Rebuilding North Korea's navy as a submarine-heavy junior force

How should North Korea rebuild its navy to support China in a future major war?

The suggested role is local sea denial by conventional submarines, freeing Chinese boats for other missions, with land-strike capability as an additional possibility.

In the hypothetical role as a junior partner to China, North Korea is assigned a mainly submarine contribution. Conventional submarines could help keep hostile forces away from allied waters. Covering those local duties would free Chinese boats for other work. A land-strike capability is also suggested to add uncertainty for South Korea.