Slitherine

As a unit class, they should all be able to attack subs as, per the rules, only destroyers and tactical bombers can attack subs. However, there are 3 recon units that are lumped in the TB class that have a '0' naval attack value so would not be able to do so.

I was wrong in assuming that Stukas cant attack subs (i guess i somehow got that impression from my first play-through of Sea Lion 41 scenario, idk why). However, i was surprised even more yesterday, when i discovered that even BF110 with 2 hex vis range can not spot the sub so i moved a battleship into the waters that i deemed safe and sub-free and ran into a sub. Does anyone know clear rules of submarine detection?

As far as I understand it, if the sub is submerged, you won't see it. I'm on the EF, so it's been a while since I saw a sub... but I think the only way you know if a sub is there is if you are directly overhead it and the attack option is offered. The visibility range is for units that are "visible" (above ground). As I say, it's been a while, so someone may correct me.