For whoever has problems, read Eduard0 review: you can drag down the list of the ships, so you can buy new powerful ones.
There a lot more ships than the first couple which are clearly visible, just click and drag down.
I bought all the ones in the "war fork", upgrading them fully as soon as I could, and no mission was a problem.
By the way, if you think the battles take too long, keep in mind that you can shot more than one load of cannon balls at once. Near the end I used to double click all the enemy ships, shooting 2x each one of them, and then shot more the once which have survived. It made the battles very fast.
Now, about the game, I agree with eduard0: discover that you can buy more ships is a bit "tricky" since there is no hint that you can drag down the list. The same for the achievement list.
Moreover eventually it becomes repetitive since when you have the best ships fully upgraded, you can sink everything pretty easily.
Even the final boss at the end was anti-climatic, since it can be defeated in the first round (not going to say here how, because I don't want to spoil the readers, but it's really easy to figure out).
Now that I've said all the bad, let's move to the good.
The game is nice, both graphically and conceptually, and I had a good time -even if pretty short- in playing it. And if the shortness and easy final part don't make it a long standing time waster, on the other hand this means the game doesn't become long to the point it becomes boring.
It surely deserves a run.
4 stars (hoping the author will manage to find a way to make clear that you need to "drag the lists" to buy all the ships :P).