Alien Retaliation

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Alien Retaliation mission type.

The most overtly aggressive of the Alien Missions, Alien Retaliation signifies an alien attempt to destroy X-Com via military force. Alien Retaliation missions are generated in response to X-Com's activities, in a form of dynamic difficulty.

The mission is performed in two stages. First, a series of UFOs (Small, Medium and Large Scouts, and eventually two Battleships) will appear and carefully fly over the targetted zone, searching for an X-Com base. This search can be hampered by shooting down the scouts, or by construction of Mind Shields. If the scouts succeed in finding a base, the scouting phase will end, and a Battleship will appear to assault the base. An attacking Battleship can be destroyed by Base Defence Systems, or (if the base is manned) its strike force can be fought off in a Base Defence mission; otherwise, the base is destroyed.

The aliens do not score from this mission beyond the ordinary points for UFO presence; however, losing a base is a direct material blow to X-Com. Furthermore, if X-Com loses all its bases to Alien Retaliation, you will immediately lose the game.

Causes of Retaliation

There are two distinct ways an Alien Retaliation mission can begin.

  • A "triggered" Retaliation mission is a specific response to a single X-Com act. Every time X-Com shoots down a UFO in air combat, there is a chance (modified by difficulty level) that an Alien Retaliation mission will immediately be generated. Retaliation missions generated in this manner will always be performed by the same race that crewed the UFO shot down, and will be performed either in the zone of the shootdown (which may not even contain a base), or the region from which the offending X-Com craft originated (the latter is more likely on higher difficulties). Note that performing a UFO Ground Assault will never trigger Retaliation.
  • A "scheduled" Retaliation mission is a more general response to the ongoing threat posed by X-Com, and is assigned at the beginning of a new month like other Alien Missions. These will begin either when X-Com researches The Martian Solution or if the game goes on beyond a certain month (which month that is depends on difficulty), and occur once per month for the rest of the game in addition to the aliens' other activities. Scheduled Retaliation missions are performed by a random race (20% for each, regardless of month), and will always target the oldest X-Com base that doesn't already have a Retaliation mission looking for it.

Difficulty table

Difficulty Beginner Experienced Veteran Genius Superhuman
Chance to trigger Retaliation per interception 4% 8% 12% 16% 20%
Chance Retaliation targets interceptor's home base 50% 56% 62% 68% 74%
Latest month at which scheduled Retaliation begins Mar 2000 Feb 2000 Jan 2000 Dec 1999 Nov 1999


  • None of the UFOs performing Alien Retaliation will land. This can be diagnostic of Retaliation activity if X-Com lacks Hyper-Wave Decoders, and also means that UFO Ground Assault is impossible; X-Com must shoot down Retaliation scouts in order to perform UFO Crash Recovery.
  • To distinguish between Battleships that are merely acting as scouts for an Alien Retaliation, and those that are on an attack run, pay attention to their flight patterns. A Battleship on a scouting mission will arrive in the targetted zone at Very High altitude and top speed, and then slow down to much lower speeds to perform several passes at Very Low altitude. A Battleship on an attack run will immediately descend to Very Low altitude, and charge straight for the base at a full 5000 knots. This means that an attacking Battleship can only be shot down by an Avenger.
  • There is a design oversight in the code that monitors whether an X-Com base has been found and is due for an attacking Battleship. A flag in XBASES.DAT is set when a scouting UFO detects the base, which triggers a routine to spawn a Battleship on an attack run. The flag is removed when a Base Defence mission occurs - and only when that mission occurs. Shooting down the Battleship, or destroying it with Base Defence Systems, will not remove the flag, causing another Battleship to attack a few days later. This will never end until a Battleship is allowed to invade the base.

UFOpaedia description

If XCom interceptors are being particularly successful in shooting down UFOs then the aliens may take some retaliatory action. This could result in a direct attack against an XCom base. However, the aliens have to find an XCom base in order to attack it, and provided UFOs are kept away then there should be little danger of an assault.

See Also

Base Defence

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