This is my entry for Ludum Dare 29. The theme is "beneath the surface".
Scientists working in an undersea lab have developed a powerful new weapon, codenamed "Tethys". Bad guys have got wind of this: they're coming to destroy the lab, so they can claim it for themselves. Your job is to defend the lab. You have a submarine equipped with all the latest technology; how long can you keep the attackers at bay?