UFO: Enemy Unknown & Terror from the Deep

UFO: Enemy Unknown (later released under the title X-COM: UFO Defense in the United States and X-COM: Enemy Unknown for the European market) and Terror from the Deep are turn-based games situated on Earth. Your main task is to defend Earth and to encounter and destroy UFO main base.

You are able to develop better technologies, construct Earth bases and discover new types of aliens. The game is divided into two parts. In the first part you build up your base, order your scientists or prepare ships and soldiers for missions. The second part is in turn-based mod where you control your soldiers on battle map. Onto these maps you must fight aliens and save civilians.