Attacking subs off the coast with land units

When attacking a sub on a coast the att/def box shows 0 att and 0 def.
this dosnt always happen but does most times.

iv canceled the move to attack order and replaced it and it then shows correct att/def but rarely.

Happened again when attacking a city this that that had battleships.

It shows 0/0 but i'm pretty sure the battle goes on normal

Yes it does, but the problem is i need to know the true att/def so i dont send my units in to a losing battle.

You actually can destroy a sub with a tanks near coast in reality maybe with guided shells =P