This was a really solid entry, and the opening crawl was really well done and got me excited for the game as a whole! The game itself reminded me a bit of the board game Plunder, as well as Advance Wars.
I think being able to move after attacking might add some complexity- because you can only move before attacking, I ended up falling into the general strategy of mostly waiting around the starting area and having opponents come towards me, and once they were in range, I didn't find much incentive to move around much, instead just attacking. When I did try to go on the offensive, I ended up losing a significant amount of health, but that's maybe a skill issue resulting from how I chose to compose my fleet? That said, I don't know if allowing post-attack movement would ruin the game's balance!
Also, I think a tile that acts as a wall that blocks attacks could be good- I didn't make it to the last couple of levels, so maybe that is a mechanic that I didn't encounter. Another smaller suggestion is that having the 'water' tiles animate with moving waves would add some visual interest and increase the presentation of the levels.
I know this sounds critical and I'm just spitballing here, but I had a really good time with this, and I could tell that a lot of love and care was taken in making it. The music and presentation were very well done, I liked the shop, and including an in-game tutorial was very appreciated. Good job all around!