Alien Missions in Enemy Unknown (OpenXcom)

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

• Alien Research
• Alien Harvest
• Alien Abduction
• Alien Infiltration
• Alien Base
• Alien Terror
• Alien Retaliation
• Alien Supply

Alien Missions Frequency

The aliens will generate new missions each month according to the following pattern:

• January, 1999: 1 Alien Research, 1 Alien Terror, shooting down UFOs may trigger an Alien Retaliation mission.
• February to May, 1999: 1 random mission, 1 Alien Terror, shooting down UFOs may trigger an Alien Retaliation mission.
• June, 1999: 2 random missions, 1 Alien Terror, shooting down UFOs may trigger an Alien Retaliation mission.
• After The Martian Solution is researched OR depending the difficulty level (March 2000 on Easy or November 1999 on Superhuman): 1 Alien Retaliation mission is added, in addition to the above.

Alien Missions Selection

The game will create an array of possible missions for each region of the world to be used when randomly selecting missions for each month. The random missions assigned to each region can be of 5 kinds: Alien Research, Base, Abductions, Harvest and Infiltration. Alien Terror, Retaliation and Supply missions are special cases and are not present in this array since those missions are automatically generated.

Once a particular mission is selected it will be removed from the array and won't appear again for that region. If all of the missions in the array are used then the game will restart this process and refill the mission array.

First the game will randomly choose a region for the mission, using weighted factors (defined on the ZONAL.DAT file) to influence the probability of each region being selected:

• North America: 18
• Arctic: 4
• Antarctic: 4
• South America: 10
• Europe: 16
• North Africa: 12
• South Africa: 8
• Central Asia: 12
• Southeast Asia: 15
• Siberia: 10
• Australia: 10
• Pacific: 5
• North Atlantic: 5
• South Atlantic: 5
• Indian Ocean: 5

The 3 last regions don't have any random missions assigned and they won't see any Alien Terror missions since they have no cities present. However, it will be possible to see Alien Retaliation missions if any UFOs are shot down over those areas.

As said above, each region has several missions assigned. The mission will be randomly selected also based on weighted factors (defined on ACTS.DAT, which are shown on the table below.

Regions	Research	Harvest	Abduction	Infiltration	Base
North America	14	17	20	20	20
Arctic	25	NA	NA	NA	35
Antarctic	25	NA	NA	NA	35
South America	10	24	12	18	22
Europe	10	10	15	20	6
North Africa	8	8	8	8	19
South Africa	7	8	8	8	9
Central Asia	5	5	6	10	8
Southeast Asia	8	13	21	13	8
Siberia	6	NA	4	NA	9
Australia	15	11	4	8	16
Pacific	15	NA	NA	NA	27

See Also

• Alien Life Forms
  
• UFOs
  
• Research