Codex Gamicus

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) is a critically-acclaimed strategy video game created by Julian Gollop. It is the first entry in the X-COM series.


The story of X-COM begins in 1998. The initial plot centers around increased reports of UFO sightings. Tales of abduction and rumours of attacks by the unknown aliens become widespread. The nations of the world come to perceive this as a threat and attempt to form their own forces to deal with this, such as Japan's Kiryu-Kai force; these forces fail miserably, the Kiryu-Kai not intercepting a single UFO in its five months of operation. On December 11, 1998, representatives from some of the most powerful nations in the world meet in Geneva, Switzerland, to discuss the issue. From this meeting was born the secret paramilitary organization Extraterrestrial Combat Unit (X-COM), over which the player assumes control at the start of the game.

The player manages X-COM throughout the game, battling aliens. As the game progresses, the player learns more and more about the enemy, their species, sub-species, mutated creations and technology. It is revealed that the aliens are led by creatures of immense mental power called Ethereals, and that the their main base located on Mars, in region known as Cydonia. It is up to the player to fully prepare the final assault team, attack Cydonia and destroy the mastermind behind the alien invasion, the Alien Brain.


The game takes place within two main views: the Geoscape and the Battlescape. It begins on January 1, 1999, with the player choosing a location for their first base on the Geoscape screen. The Geoscape screen is a global view representation of Earth as seen from space, which displays X-COM bases and aircraft, detected UFOs, alien bases, and sites of alien activity. The player can view the X-COM bases (one in the beginning), make changes to them, equip fighter aircraft, order supplies and personnel (soldiers, scientists and engineers), direct research efforts, schedule manufacturing of advanced equipment, sell alien artifacts to raise money, and deploy X-COM aircraft to either patrol designated locations, intercept UFOs, or send X-COM ground troops on a mission in a transport aircraft.

Funding is provided by the sixteen founding nations of X-COM. At the end of each month, a funding report is provided, where nations can choose to increase or decrease their level of funding based on their perceived progress of the X-COM project. Any nation may quit, if the player's service is deemed unsatisfactory or the nation's government has been infiltrated by the invaders, the force loses monetary support from that nation. Through reverse-engineering of recovered alien artifacts, X-COM is able to develop better weapons, armour and vehicles to combat the alien menace, and eventually uncover how to defeat them.

Gameplay switches to the tactical combat phase known as the Battlescape whenever X-COM soldiers come in contact with aliens. Here the player commands human soldiers against the alien forces in an isometric turn-based battle. One of three outcomes is possible: either the X-COM forces are eliminated, the alien forces are neutralised, or the player chooses to withdraw. The mission is scored based on the number of X-COM units killed, civilians saved or killed, aliens killed or captured, and the number and quality of alien artifacts obtained. Troops may also increase in rank or abilities, if they made successful use of their primary attributes (e.g. killing enemies). Instead of experience points, the combatants gain points in skills like Psi or Accuracy, a semi-random amount depending on how much of the action they participated in. In addition to personnel, the player may have vehicles such as HWP unmanned ground vehicles outfitted with weapons and armour. Recovered alien artifacts can then be researched and possibly reproduced. Recovery of live aliens may produce information, possibly leading to new technology.

The game has eleven fictional races of aliens. Each race has various strengths and weaknesses, and some races are dependent on other races. The aliens come to Earth from a large base on Mars, but their origins are unknown. One reason for the game's success is the strong sense of atmosphere it evokes. Soldiers are vulnerable to alien attacks even when armoured, and the use of features such as night-time combat, line of sight and opportunity fire allows for alien sniper attacks and ambushes. The enemy comes in numerous forms, and players run into new, deadly aliens repeatedly without any knowledge of their characteristics and capabilities beforehand.

The game may end in several ways. If the player's performance is poor for two consecutive months, the player runs a deficit for two consecutive months, or all the player's bases are captured, the game ends in defeat. If the player mounts an assault on the aliens' main base and loses, the game ends in defeat. If, however, the player is victorious in the final assault, the game ends in victory.

Unofficial game editing software is available allowing players to change the qualities of weapons and equipment, and to change the standard maps and layouts of UFOs that were provided with the game. Fan-made patches also fix a bug which results in the player always playing the game on the easiest difficulty, no matter what difficulty level has been selected (which was not fixed in the official patches).


X-COM was originally conceived by Julian Gollop and his brother Nick as a sequel to his 1988 game Laser Squad. The initial 1991 demo presented a relatively modest, two-player tactical game. The Gollop brothers approached several global publishers including Krisalis and Domark with an early demo of the game for the Atari ST (then known as Laser Strike 2), eventually brokering a deal with MicroProse, producer of Sid Meier's Civilization. Although supportive of the project, the publisher expressed concerns that the demo lacked a grand scale in keeping with its just-released Civilization smash hit. Under MicroProse's direction, Gollop changed the setting to modern-day Earth and expanded the strategy elements, among them the ability to capture and reproduce alien technology. MicroProse graphics artists John Reitze and Martin Smillie also helped Gollop to provide visuals for the PC version; John Broomhall composed the music. Another working title was X-COM: Terran Defense Force. The game was nearly cancelled twice, first due to the financial difficulties and the second time under the pressure from Spectrum HoloByte after it had acquired MicroProse, but eventually completed in March 1994.

Gollop has cited the television series UFO, as well as the writings of Timothy Good, as influences for the storyline of X-COM, particularly the psionic powers of the various extraterrestrials. Good's 1991 book Alien Liaison provided inspiration for several of Gollop's revisions, including the notion that world governments might seize alien technology or secretly conspire with the invaders (a negative result which can occur in-game). Despite numerous changes from the demo, X-COM remains true to the turn-based strategy layout of Laser Squad and the Rebelstar series, also developed by Gollop. The artificial intelligence of those games formed the basis for X-COM's enemy tactics, with Gollop programming his own unique algorithms for pathfinding and behaviour; in particular, X-COM's aliens were purposely given an element of unpredictability in their actions, giving the illusion of a lifelike, resourceful enemy.

The finished product was marketed in Europe and Australia as UFO: Enemy Unknown, and in North America as X-COM: UFO Defense. The game was released to great acclaim, quickly selling more than 600,000 units on the PC platform alone (not counting the later ports to the Amiga computers, Amiga CD32 and PlayStation). Half of X-COM's net sales were in the United States, a rarity for a European title at the time. Gollop has attributed the game's stateside success to its title, as the television series The X-Files had premiered a year earlier.


Two ports were created by the MicroProse team in 1994-1995:

  • The Amiga versions display lower-quality graphics than the DOS version (less noticeable in the AGA Amiga version), however the sound is improved. A Limited Edition for the Amiga CD32 included a MicroProse travel alarm clock.
  • The PlayStation port retains the original graphics and features much higher-quality music than the DOS version (several CD tracks instead of MIDI music). It is compatible with PlayStation Mouse and requires five memory card blocks for a Battlescape saved game.


Entity Award
Computer Gaming World #22 "150 Best Games of All Time" (1996)[3]
PC Gamer #15 "Readers All-Time Top 50 Games Poll" (2000)[4]
IGN #1 "Top 25 PC Games of All Time" (2000)[5]
PC Gamer #15 "Readers All-Time Top 50 Games Poll" (2000)[4]
IGN #1 "Top 25 PC Games of All Time" (2000)[5]
Computer Gaming World #10 Best Game of All Time, by readers (2001)[6]
Computer Gaming World #3 Best Game of All Time, by staff (2001)[6]
PC Gamer #3 "Top 50 Games of All Time" (2001)[7]
PC Gamer #8 "50 Best Games of All Time" (2005)[8]
Computer Gaming World Hall of Fame (2005)[9]
IGN #1 "Top 25 PC Games of All Time" (2007)[10]
Pelit #2 Best Video Game Since 1992 (2007)[11]

As of 2010, the game holds an average magazine review score of 93.60% for the PC version[12] and 92.90% for the PSX version,[13] according to GameRankings. According to Amiga HOL database, the various Amiga ports hold the average ratings of 79% on ECS/OCS Amigas,[14] 82% on AGA Amigas[15] and 73% for the Amiga CD32 version.[16]

Since its release, X-COM: UFO Defense was named the #1 PC game of all time by IGN in 2000, 2007 and 2009;[5][10][17] the #3 best computer game of all time by Computer Gaming World and by PC Gamer in 2001,[6][7] and the #2 best video game since 1992 by Pelit in 2007.[11]


The game has been re-released as part of the compilations X-COM (Collector's Edition) by MicroProse in 1998, X-COM Collection by Hasbro Interactive in 1999, X-COM: Complete Pack by 2K Games in 2008 and 2K Huge Games Pack in 2009. It can be also found on the "Classic Games Collection" CD featured with the July 2000 issue of PC Gamer.


X-COM: UFO Defense - A Novel is a 1995 novel by Diane Duane based on the game, which takes place during a late-game period. The book tells the story of Commander Jonelle Barrett of X-COM in her fight against the aliens.

Another novelization of the game, Враг неизвестен ("Enemy Unknown") written by Vladimir Vasilyev, was published in Russia in 1997. The book tells the story of one of the original eight X-COM soldiers from the beginning of the conflict to the destruction of Cydonia base.

Fan projects[]

  • UFO2000: a free, open source, multiplayer, turn-based tactical squad simulation based on Enemy Unknown.
  • X-Com: Tactical: a free board game, aiming to reproduce the squad tactics element of X-COM: UFO Defense. It also borrows the graphics from the original.
  • UFO: The Two Sides: a freeware (not open source) remake of the original game, featuring single/multiplayer mode, better graphics, gameplay balancing/changes and new features.
  • OpenXcom: an open-source, multiplatform reimplementation meant to faithfully mimic the original game, with optional add-ons.
  • UFO: Alien Invasion and Project Xenocide: two free open source PC strategy games heavily influenced by the X-COM series.
  • Enemy Unknown Extended: a set of mods which fixes bugs and add new features.
  • Pocket UFO: a re-implementation of the game for the Windows PDA platform.
  • XcomUtil: a command-line utility which allows for many changes and enhancements to be easily made to the game. It can even allow two-player battles.
  • Dimmignatt, Floaf - X-Com V2: a remake of the game's introduction music.


  1. X-COM: UFO Defense Review for PC - GameSpot
  2. X-Com: UFO Defense - PlayStation Review at IGN
  3. Computer Gaming World, 15th Anniversary Issue, November 1996
  4. 4.0 4.1 PC Gamer, April 2000
  5. 5.0 5.1 5.2 The Top 25 PC Games of All Time. IGN (July 24, 2000). Retrieved on 2008-06-20
  6. 6.0 6.1 6.2 Computer Gaming World, 20th Anniversary Issue, March 2001
  7. 7.0 7.1 PC Gamer, October 2001
  8. PC Gamer, April 2005
  9. CGW's Hall of Fame. (March 23, 2005). Retrieved on 2009-08-09
  10. 10.0 10.1 Adams, Dan; Steve Butts, Charles Onyett (March 16, 2007). Top 25 PC Games of All Time. IGN. Retrieved on 2009-08-07
  11. 11.0 11.1 Pelit 8/2007, page 64
  12. X-COM: UFO Defense for PC - GameRankings
  13. X-COM: UFO Defense for PlayStation - GameRankings
  14. UFO: Enemy Unknown reviews (ECS/OCS)
  15. UFO: Enemy Unknown reviews (AGA)
  16. UFO: Enemy Unknown reviews (CD32)
  17. Ocampo, Jason; Steve Butts, Jeff Haynes (August 6, 2009). Top 25 PC Games of All Time. IGN. Retrieved on 2009-08-07

External links[]