Nice submission, and cool interpretation of the theme! It's a small detail but zooming in and out on the square when you're upgrading it or starting a level, and the cannons staying exactly where you placed them was a really nice touch - I think it actually really helped the game feel smooth and nice to use. Though it's a shame the enemies only spawn where they do - I didn't need to move at all to beat the levels as I could just stay still and hit the i, k and l buttons quickly. If that was changed then it could be a very fun game.