Fun! Reminds me of Missile Command.
It's missing some player feedback - some kind of "health" display of the diver, success feedback when you defend treasures, and some indicator as to the role of the ship (does the diver have to return to the ship? Are there a limited number of divers aboard the ship that it spawns when one is defeated?).
Good job for getting so much done! It's clear you had a cool vision for the game :)