I wanted to remake an old C64 submarine game what I loved as a child, but after making some sketches, I found it too difficult to make an exciting and long enough level for it, so finally dropped the idea. maybe with limited amount of torpedos and bombs, and with some strange large deep-water animals (like a mutant octopus) could make the level exciting, discovering underwater labyrinths, requiring breaking through walls by explosives (causing self damage if wrongly used). but probably a non-vehicle idea would be better.