UFO: Enemy Unknown (later released under the title X-COM: UFO Defense in the United States and X-COM: Enemy Unknown for the European PlayStation version) is a video game created by Julian Gollop and published by MicroProse Software in 1993. It is the first game in the X-COM series.
On January 1 1999, X-COM's first base became operational, beginning what would later become known as the First Alien War - a period of time lasting three years. Hundreds of UFOs were intercepted, but forces sent to clean up the crash sites took heavy casualties. Major cities came under attack by the alien forces, and at one point the alien forces even began establishing bases on Earth itself. From these sites, however, valuable knowledge and artifacts were recovered; aliens from several distinct species were captured, studied and eventually interrogated, and their technology was reverse-engineered and put to use by X-COM forces.
In later years, the major breakthrough came—an interrogation revealed the alien's forces were based in Cydonia, on Mars. A heavily armed and armored strike force was sent to Mars in X-COM's Avenger craft (based on alien technology) and managed to destroy the alien brain creature that was apparently responsible for masterminding the entire operation. Shortly before the Cydonia base was destroyed, however, a mysterious transmission was beamed back to Earth from the wreckage of the base, setting the stage for the sequel.
Clicking on a base on the Geoscape screen takes the player to the base screen. From here, the player can purchase weapons and other equipment, recruit soldiers, scientists, or engineers, build expansions to the base, build new bases (up to eight in total may be complete), and organise research and production.
Funding for the above is provided by the ten 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. Alternatively a nation can sign a pact with the aliens which results in withdrawal of all funding by that nation to the X-COM project.
When a craft is sent to land at a UFO crash site, landed UFO, or alien terror site, the game shifts to a tactical phase known as the Battlescape. Here the player commands their soldiers against the alien forces in an isometric turn-based battle sequence. One of three outcomes is possible in this phase: either the X-COM forces are eliminated, the alien forces are eliminated, or the player chooses to withdraw. These battles lead to recovery of alien artifacts which can then be researched and possibly reproduced at the X-COM bases, and can also lead to the recovery of live aliens which may then be assigned as a research project to produce information, possibly leading to new technology.
The game may end in several ways. If the player's performance (as judged by the founding nations) 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 alien's primary base and loses, the game ends in defeat. If, however, the player is victorious in the final assault, the game ends in victory.
The OCS/ECS, AGA Amiga, and PlayStation versions feature higher quality music, and the latter is compatible with the PlayStation mouse. It requires a whole memory card for the Battlescape save games. The same applies to the sequel.
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.
No expansion packs for UFO Defense were released, but several sequels were. X-COM: Terror from the Deep was the first sequel to X-COM, and was developed in-house by Microprose. X-COM: Apocalypse was a new game developed by the Gollop brothers that was set in a single city, rather than the entire planet. It featured similar gameplay to the prior games, albeit with both turn-based and real-time combat. This was the last X-COM game developed by the Gollops. X-COM: Interceptor was a flight simulator set in deep space with some strategy and research elements like X-COM. X-COM: Enforcer is a third-person shooter with very different gameplay to the rest of the series. X-COM: Genesis, planned to be the rebirth of the strategic roots of the series, was started in 1999, but canceled by Hasbro Interactive later that year.
The games from the X-COM series have been sold in different packages as they were re-released in later years, the most notable of which was a combination of the first five games:
The intellectual property rights to the series were retained by the publisher, and Gollop played no role in the series post-Apocalypse. The game Laser Squad Nemesis, developed independently by Nick and Julian Gollop, features several similarities to the X-COM games.
Another reason for the game's success is the strong sense of atmosphere it evokes. Soldiers are vulnerable to alien attacks even with armor, 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 shapes and forms, and players run into new, deadly aliens repeatedly without any knowledge of their characteristics and capabilities beforehand.
X-COM: UFO Defense was voted as the #1 PC game of all time by IGN and the #2 video game since 1992 by Pelit in 2007.