Ships can only attack land with the amphibious assault support shot in the first round. Like when I attacked Australia - I rolled a “4” for the battleship support shot. It only fires in the first round of the combat, and you can only fire one support shot for each ground unit unloading (you can’t shoot twice with battleships/cruisers when you’re only unloading one infantry, for example). This is the only time that ships can attack units on land (only cruisers and bships).
A surprise attack with a sub is it’s ability to shoot first and also to sink an enemy ship without return fire. This ability can only be used if there are no enemy destroyers in the battle.
Example:
You attack me with 2 subs and a destroyer. I have a sub and a destroyer.
1) First round, neither of us gets a suprise attack. Let’s say you get a hit and I get a hit in the first round.
2) Let’s say I lose my destroyer and you lose a sub.
3) Now it’s 1 sub and 1 destroyer vs. 1 sub
4) I still do not get surprise strike nor can I submerge, because you still have a destroyer.
5) Since my destroyer is gone, your sub now gets all abilities back.
6) Your sub now gets a surprise attack every round for the rest of the battle. If you lose your destroyer, then my sub can submerge, or if I do not submerge, our subs basically attack at the same time (like a normal battle - we both get to roll)
7) So with your 1 sub and 1 dd vs my 1 sub, if you roll a 2 with your destroyer my sub still fires back (at a 1). But if you roll a 2 with your sub, my sub is hit with your surprise attack and I don’t even get to roll.
Say you attack a cruiser with a sub. If the sub rolls a 1 or a 2, the cruiser is sunk in that round and does not get to roll. So this battle cannot be a tie. Either the sub will miss and the cruiser will hit (cruiser wins) or the sub hits (sub wins).