I like the idea and the way you did the upgrades was really good. I thought it would just increase the number of cannonballs I fired but having it add a new cannon/angle that the ship fires at is a much better way to do it that made it more fun. The game was a bit too difficult for me, the cannonball is so small that it is often really hard to hit the enemy. I also had a number of weird hiccups where the game would freeze for a couple of seconds until I clicked again but otherwise it performed well. The audio is really solid too. Nicely done!