"X-COM: Terror from the Deep is a computer game, the sequel to UFO: Enemy Unknown, and the second part of the X-COM series. It was developed and published by MicroProse. Its interface is nearly identical to its predecessor, as is its graphics technology.
In the original game, the player was tasked with defending Earth from invasion. Now, forty years after the first alien war, that lasted for three years, was won, a new alien menace begins to emerge from the deep oceans. The game plays out underwater, with base-building and combat all being submerged beneath the waves. The only time in fact that the game moves onto dry land is for terror site missions, when the aliens attack a port, ship, or island holiday resort."
Source: Wikipedia, "X-COM:_Terror_from_the_Deep," available under the CC-BY-SA License.
