X-COM: Terror From the Deep

Summary pulled directly from Steam - Some text may only be applicable to Steam platform

The war continues... X-COM: UFO Defense brought you to a galactic battlefield. X-COM: Terror from the Deep brings the alien terror into a totally new dimension.
Seeking to take advantage of a weakened Earth, X-COM's deep space foes unexpectedly change strategy and launch a powerful second front against planet Earth.
In the dark depths of vast oceans, long sleeping forces are awakened by reanimation signals sent out across the galactic silence by their interstellar brothers and sisters. Slowly but surely, an army of hibernating alien sea creatures awakens. Your combat now extends to the strange new worlds of the deep where superior alien technologies threaten the very survival of this planet - your planet - Earth.

Sequel to the hugely successful X-COM: UFO Defense
Actual undersea geoscape mapping system with rich topographic detail
Full array of undersea military technology
Rich graphics feature water coloration and wrecks
Multilevel tactical maps featuring both underseascapes and buildings
Alien encyclopedia features mutation technology and new watery denizens