The games run very choppy on my browser! At least the first minute after clicking the start, the rest is smooth sailing (except for the ships I destroyed). I really like the concept and the mechanics! Tho I wish we could have seen the tower explode or something like that once you lose all your health, haha.
When you pause the game on browser there's a GAME PAUSED sign that is misplaced and is cut in half due to being in the lower half of the screen! It doesn't ruin the playing experience but it's maybe something you'd want to take a look at.
Overall great job! <3