If a sub has a stealth specialist on it, it will be invisible to all players, with these exceptions:

A sub with a stealth specialist will always be visible to their owner.

A gift sub carrying a stealth specialist will be visible to the player it is going to, and the player who sent it.

If a sub carrying a stealth specialist is within 25% of an outpost's sonar range, it will be visible to the player who owns that outpost.(Note that a Sentry can only fire upon a sub carrying a stealth specialist if the player who owns it can see the sub. The normal rules of which sub a sentry will target also applies.)

Flavour text: The best way to avoid defeat is not to make it obvious you won't be defeated.

This sounds horrible to play against tbh

I believe in long subterfuge past in the Alpha days, They had a specialist called the Illusionist, who worked with by misrepresenting subs.
Essentially they disbanded this specialist because it made attacking a huge frustrating gamble- Planning around a specialist that can deceive what you see is kind of a nightmare.

So if the devs felt it was unhealthy for the game then I think I'll stand by their decision for no stealth

I still like my idea of a mole for a stealthy specialist. Disguising itself as something else and giving you sonar range while captive at enemy outposts.