On Very Hard difficulty setting it is indeed hard to win. Sadly not for the reasons to AI being smart or playing well. For the simple reason that AI European players do not give up until you sink all of their ships.
If you catch them early in the game it is fine. Sadly for later battles when they have 5-8 ships it is indeed very hard to win. You destroy they on land and then wait by their original landing site and destroy each ship while it is repaired.
Sadly since you do not sink them they never go away only return and return again.
It would be good if the game had repair count and with each repair probability of ship sinking grew or a fixed limit that each ship can only be repaired 3 times and then it will sink.