Alien Retaliation
If X-COM aircraft are being particularly successful at shooting down UFOs then the Aliens will take retaliatory action in the form of an attack against an X-COM base.
An Alien Retaliation mission consists of a series of UFO scouts that will appear in the area the UFO was shot down to patrol for an X-COM base. At the end of the patrol, once the aliens have decided that they've found a base, a Battleship will appear a day or two afterwards and attack an X-COM base in the same region - picking one at random if there are several. In the worst case scenario, the aliens will sometimes skip the scouting phase entirely and immediately schedule the attack.
Once an X-COM base is marked for the attack, a Battleship will be sent to drop troops into the base, and then immediately escape into orbit. See below for a pertinent bug/feature concerning this.
A battleship on the attack is easy to spot as it will always be moving purposefully in a straight line to the base it is attacking. The ship will be moving at top speed so only an Avenger can intercept it.
If you shoot down the retaliation scouts, the next scout to appear in the patrol will be delayed by a random amount of time. However, the type of UFO may be upgraded to make it more difficult for you to shoot down. As alien mission have a set time frame for them to be completed, they will eventually abort the retaliation mission if the scouts are delayed long enough.
Note that assaulting an landed Retaliation scout when it is on the ground does not have this effect.
While the scouting parties do cause activity that will concern the Council, the aliens do not directly score for destroying the base. Beyond the material loss of the base, assets and personnel, you will only gain negative points for the soldiers or tanks killed defending the base.
Obviously, if you lose all bases to alien retaliation, X-COM will be wiped out and you lose the game.
Multiple Retaliations
Each time a retaliation mission is set up it will be run by a particular task force of aliens that are charged to find an X-COM base and get troops inside to destroy it from within. Once a team manages to drop a retaliation squad into your base, their mission will come to an end and they will cease their attack.
Each team works independently of the other, and do not share their findings with the others. So if they find a base, only they will know where it is. All other teams will have to locate the base themselves. Base locations are not retained once the mission has been completed. It may indicate that the crew on the final battleship may be what is left of the task force and the base location either dies with them if they fail, or is no longer required if they succeed.
If you are targeted by more than one group at a time, you will need to crush them all to cease the attacks altogether. Once they have all been dealt with, you will not have to worry about any further attacks until the next wave of retaliation scouts are encouraged to appear.
Base Attack Loop
Due to a programming oversight, destroying the battleship with base defenses will not clear the retaliation mission flag. Because of this the game will think that the mission is not yet over and it will prepare another battleship to attack the base. This whole process will then repeat itself until the battleship is allowed to land.
This can be exploited.
A few effects that arise from this bug are that the aliens will appear to:
- Have endless resources and can afford to send fully crewed Battleships every few days
- Have a sudden case of amnesia once the ground crew is dealt with
