Alien Missions

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UFOs are sent out periodically to conduct a number of types of Alien Missions, some of which the purpose is fairly inscrutable, others are fairly obvious in their reasoning. Especially once the Hyper-wave Decoder is deployed, knowing the mission of the aliens can help make strategic plans for further actions that the aliens may attempt in the near future.

List of Alien Missions

Generation of Alien Missions

Most new alien missions are generated by the game at the start of each calendar month. The process goes as follows:

  • Generate an ordinary mission (Research, Harvest, Abduction, Infiltration or Base).
    • If it is January 1999, this will be a Sectoid Alien Research mission in the same zone as X-Com's first base, with no consultation or modification of .DAT files. Otherwise, continue.
    • Roll on ZONAL.DAT to select the zone in which the mission will take place.
    • Roll on the selected zone's section of ACTS.DAT to select the mission type.
    • Roll on the selected act's section of Alien Appearance Ratios to select the alien race performing the mission.
    • Set the value for the selected zone/act combination in ACTS.DAT to zero (preventing the combination being used again). If the selected zone has no nonzero values remaining in ACTS.DAT, set the value for that zone in ZONAL.DAT to zero as well.
  • If it is July 1999 or later, generate a second ordinary mission, by the same mechanism.
  • Generate a Terror mission.
    • Roll on a special table in the executable to select the zone in which the mission will take place. This table looks like the starting values of ZONAL.DAT, but the Arctic, Antarctic and Pacific weights are set to zero (there are no cities in those zones). Note that this table is not modified during gameplay, so terror missions can hit the same zone more than once.
    • Roll on the Terror section of Alien Appearance Ratios to select the alien race performing the mission.
  • If X-Com has researched The Martian Solution, or if a certain time threshold has been reached, generate a Retaliation mission.
    • The time threshold is (14 - difficulty), using the game's internal numbering. This corresponds to March 2000 on Beginner and November 1999 on Superhuman.
    • The mission targets the oldest X-Com base that does not already have a Retaliation mission searching for it.
    • Roll to select the alien race performing the mission. All five alien races are equally likely; the Retaliation section of Alien Appearance Ratios is not consulted.

There are two cases in which a new alien mission can be generated during a month.

  • If an alien base is present on Earth at midnight of any day, there is a 6% chance for each base that a Supply mission will be generated targetting that base. This mission will be performed by the same alien race that founded the base (and, in UFO, mans it).
  • If X-Com shoots down or destroys a UFO, there is a chance an Alien Retaliation mission will be immediately generated. This mission will be performed by the same alien race that owned the UFO shot down. See Alien Retaliation for more detail.

Additional Research

There are also a few key research topics essential to winning the game that can be uncovered by capturing and interrogating aliens, with the more important topics requiring aliens of higher rank to uncover them. Each topic can only be researched when the previous one has been completed.

Alien Origins

The Martian Solution

Cydonia or Bust

See Also


UFO Badge X-COM: Enemy Unknown/UFO Defense
Alien Missions:Alien OriginsThe Martian SolutionCydonia or BustAlien ResearchAlien Harvest
Alien AbductionAlien InfiltrationAlien BaseAlien TerrorAlien RetaliationAlien Supply