[Thermodyne]

Diesel subs are built for costal defense, and tend to be limited on fuel stowage. But they can pack a big punch. They are much quieter then nukes when submerged, but also very slow, high speed drains the batteries too fast. The snorkels are not all that much good, airborne radar can find them in any sea state where they can be deployed. I would think that snorkels would be a good place to deploy stealth technology. The best way to deal with them is air power; active sonar negates the advantage of silent running. And once found, the lack of speed makes them sitting ducks.

The Soviets probably built the most state of the art stink boats, some were even boomers.