Following the destruction of the alien Brain on Cydonia, a transmitter remained active there which awakened a group of aliens under the Earth's seas who had lain dormant for millions of years. Terror from the Deep is set in 2040, four decades after the events of UFO Defense. A new feature added in TFTD was melee weapons, thanks to feedback from the players who suggested the idea. A part of the reason for the enhanced difficulty is that players complained of the first game being too easy, however MicroProse were unaware that this was due to a bug that resulted in it reverting to Beginner mode in the released version. Aside from lengthy multi-part missions, map layouts are more complicated, there are several types of terror missions, and weapons carry fewer rounds in their magazines.ĭifficulty levels were markedly increased compared to UFO Defense. The game features some mission types composing of multiple parts, such as alien shipping route terror attacks in which the first part is a battle of the upper floors of the ship while the second part takes places in the lower decks of the ship (all parts must be completed for these missions to be successful, and soldiers lost in previous parts do not appear in later parts). Underwater battles use the same physics as the ground ones but certain weapons cannot be used on surface/land missions. The second part, the BattleScape, is used for combat between squads of aliens and humans, and takes the form of a turn-based battle from an isometric view. The first is the real time-based GeoScape, a global view of Earth where the player views alien and X-COM craft and bases, can hire and dismiss staff, buy and sell vehicles, weaponry, ammunition and items, and build and expand bases. Just like X-COM: UFO Defense, the game consists of two parts. This is also used as a plot device all of the alien technology from the first game is unusable in salt water, forcing the player to capture and develop new technology.

X-COM: Terror from the Deep takes place mostly underwater, with base-building and combat all being submerged beneath the waves.

Xcom 2 made whole