How many fleets have you had in the Atlantic, as any power? Any more than 4 fleets, and you're probably wasting builds. And no more than two powers can ever get the full force into that battle, because two members of an alliance won't ever both have large forces in the Atlantic. If it's an even battle, they won't go through with the fight, and skirmish elsewhere until it's an uneven battle. If it's an uneven battle, then one of the sides lost some forces, and the battle will contain 7 troops or so. A big fight, but nothing amazing. Haven't seen it myself, though. Probably a rare event. The fact is, if you're fighting over the North Sea, both of you have lost already. It needs to be seized, not fought over.