Editing X-COM: Terror from the Deep (section)

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

Just like ''[[UFO: Enemy Unknown]]'', the game consists of two parts. The first is the [[Real-time strategy|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. The second part, the BattleScape, is used for combat between squads of aliens and humans, and takes the form of a [[turn-based tactics|turn-based battle]] from an [[Isometric graphics in video games|isometric view]].

Underwater battles use the same physics as the ground ones but certain weapons cannot be used on surface/land missions. 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). 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.

Difficulty levels were markedly increased compared to ''UFO: Enemy Unknown''. 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. A new feature added in ''TFTD'' was melee weapons, thanks to feedback from the players who suggested the idea.