In the 1st edition rule book it is explained that ships can support an adjacent battle:
Ship units may support adjacent combat in a sea area or a ...
But what if I'm attacking from a spot that touches water, into a spot that does not touch water? The rules don't ever specify what the battle area is. It makes intuitive sense that the ships wouldn't actually be able to cross land, but since the rules don't specify the answer it has become a question for my gaming group.
This would also be the question for land units. Do the units need to be touching the defending land/sea area? Or would they be allowed to be called in from areas adjacent to the attacking land area?