Alien Missions (Long War)
For Alien Missions involving multiple UFOs, usually the last UFO needs to be defeated to foil the mission. Larger ship types become available for a mission only if the aliens have enough resources, and the final ship chosen will be a random selection of those available. For example, if the aliens are weak then they will randomly send either a Scout or Raider for research, if they are strong then they could randomly send a Scout, Raider, Abductor or Terror Ship for the same mission.
If the aliens send a UFO and it is damaged, destroyed or lost, the aliens will pay resources for it, limiting their options in the next month.
The aliens have a strategy in Long War, and tend to focus on geographic locations. Expect to fight them the most in the continent where they lay their first base. [1]
Mission Types
Research
A Scout, Raider, Abductor, Terror Ship or Assault Carrier will fly near NOE, land for a while, and then fly off. This mission will grant the aliens research if successful, which will slowly but permanently increase the capabilities of their ground troops and UFOs.
Even though the nature this mission type seems to be non-combative, research vessels tend to be well-guarded by dozens of high-level aliens, even if the ship in question is a tiny Scout. This is especially true if these UFOs didn't suffer casualties by being shot down. On the other hand, an intact UFO will yield more alien corpses, captives, and artifacts.
If the aliens have no resource (0/4) to spare, the aliens will never undertake research missions; Contrarily, if they already have too many resources (4/4), then the maximum amount of research missions will be performed (three per month.) Otherwise, the aliens will adjust the amount of research mission attempts depending on XCOM’s threat level and the amount their resources. If the aliens do not recognize XCOM as a real threat, they will be content with the tech they are currently fielding, thus will not carry out research missions; but as XCOM is perceived to be more threatening, the aliens will try to keep up via research as much as they can afford it.
Scout
A Scout, Raider, or Battleship will fly low and around the target country, attempting to confirm the existence of XCOM satellites there. Successful scouting missions will be followed up by a new sortie to hunt the compromised satellite. It is possible that the hunting UFO will be stronger or weaker than the scouting one, so the priority to intercept this mission can vary.
A scout mission can fail in four ways: 1) the UFO is shot down, 2) the UFO could botch the mission due to sustained damaged, 3) the target country could fend off the mission by itself, or, if all else fails, 4) the UFO could simply get unlucky. The odds of these failures happening are as follows:
- Downed: 100% - if it's shot down they will always get nothing.
- Damaged: (100 - RemainingUFOHP)% - this means XCOM can commit less and gamble on merely damaging the UFO.
- Defended: (CountryDefense/2)% - the shield representing a country's defense is shown in the Situation Room and is improved by fulfilling their requests; maximum chance is 50% with 100% CountryDefense.
- Damned: (60 - AlienResearch/15)% - 900 research points guarantee aliens a successful scouting mission if not interfered.
The aliens will always send at least three scouting sorties per month, and more if they have resources to spare and perceive XCOM to be a credible threat, up to a maximum of six sorties per month.
Harvest
A Transport, Harvester, Raider or Scout will fly NOE and land in a randomly selected country. An unimpeded harvest grants the aliens resources. Which will allow the aliens to field ground troops and UFOs in greater quantity and quality.
If the targeted country has a satellite, there is a 12.5% chance per XCOM threat level (up to 50% at level 4) that the aliens will re-roll its target once and will pay a price in the process. This represents the power projected by a strong XCOM forcing the aliens to settle for sub-optimal harvests. As the aliens' first choice for harvest is randomized, more satellite coverage means a higher chance that the aliens need to waste resource to even start a harvest mission.
The aliens' tendency to perform harvest missions is the exact reverse to their tendencies to send out research missions. If the aliens have minimal resources (0/4), then a maximum amount of harvest mission is attempted (three per month); if they have too many resources (4/4), then no harvest will occur. Otherwise, the aliens will harvest more when they are shorter on resource. Additionally, the aliens also prefer doing harvests when they are not threatened; in the presence of a strong XCOM they prefer more aggressive missions instead.
Hunt
A Fighter or Raider will fly at high altitude over a previously scouted satellite-covered country, seeking to destroy the satellite. Later on with sufficient research (specifically >=75), the aliens will send a Destroyer or Battleship to hunt instead of a Raider.
The aliens will prioritize getting rid of satellites over withdrawn ex-council-members, as they have bases in such countries and without a satellite over them XCOM cannot assault it. Next, the aliens prefer satellites that protect panicking nations, and in doing so potentially forcing said nations to withdraw XCOM support, and to be controlled by them
Successful hunts will destroy the satellite in question. The base chance of success is 60%, or 90% on the second pass (30%/50% respectively if stealth satellites is researched). Damage sustained by the UFO will reduce this chance further, with 50% or less HP leading to an automatic failure.
Pertinant to this specific mission type, a 50% HP UFO will start flaring up in the aerial combat screen, as if it was being hit by multiple missiles continuously. When this happens, XCOM can order their interceptor to disengage, preventing further risks while stopping the hunt mission.
Note that the aliens can dispatch hunt missions directly, without needing to scout first; although this will only occur if XCOM is seen as a threat. The more threatening XCOM is and the more resources the aliens have, the more direct hunt mission is sent, up to a maximum of four per month.
Bomb
A Fighter, Destroyer or Battleship will fly NOE and around the target area bombing civilians. This mission will cause a lot of panic if successful. Uniquely, this is one of the few NOE mission types that doesn't land, and the only way to completely stop it is to shoot the bombing UFO down; although, damaging the UFO will reduce the amount of panic created at the end of its mission. An unfettered air raid generates 8 panic in the country raided. An additional 2 panic is added,if the UFO is ignored.
The aliens will send out more bombing missions if they have spare resource and perceive XCOM as a threat. With maximum resource and threat level they will conduct three bombing missions per month. The only exception to this trend is when the aliens have maximum resources and completely unthreatened, in which case they will divert more of all those resources into bombing missions, spawning four per month instead.
Abduction
An Abductor will fly NOE to the target area and generate an Abduction site. A successful abduction will increase panic in the country by 25, and panic across the continent by 20 (in all difficulties but normal). Thwarting the abduction will decrease panic in the country by 2.
The true motivations behind these abductions was never clear, it doesn't increase alien research, nor does it gain them any resources; and it certainly isn't the most efficient way to spread panic if it's about strategic warfare.
In many ways abduction is the least agressive mission type, perhaps due to this, the aliens will scale back on abduction attempts if they feel threatened by XCOM. But the aliens still dispatch more abduction missions if they have more resources, up to a maximum of 5 per month with max resource and unthreatened. Conversely, if the aliens are short on resource, and deem XCOM to be a priority, a minimum 2 abductions per month is attempted.
Terrorize
A Terror Ship or Assault Carrier will fly NOE to the target area and generate a Terror site. The aliens will terrorize the most panicked nation roughly 75% of the time. There is a limit of 2 terror missions per month, but they can be stacked at the end and beginning - unlucky commanders who have ceded many resources to the aliens may see as many as four in a short period of time. Terror missions are resource-intensive, and keeping the aliens on their toes should limit their ability to generate them.
Terror missions increase panic by +2 in the targeted country/+1 continent-wide per civilian killed, so these missions are always likely to see some benefit for the aliens. Losing or ignoring the mission will cause the immediate construction of an Alien Base in the country, and increase panic continent-wide by 20.
If the Terror Ship or Assault Carrier is badly damaged by XCOM interception attempts, it may abort its mission and return to base - though it's not easy without good craft and weapons. If forced to withdraw, the UFO will sharply change direction (generally doubling back towards its point of origin) and accelerate to maximum speed. Whilst further interception attempts are unlikely to catch up with it (making UFOs on terror missions some of the hardest to actually shoot down), simply avoiding a potentially costly terror mission can be worth the initial risk.
In late game up to 4 ships with Terrorize Populace mission via Hyperwave decoder may be seen. For each planned Terror site, first the Terror Ship will fly over targeted country. After several days, Assault Carrier will arrive. The Terror Ship appearance may be useful information where to relocate Firestorms. Shooting down Terror Ship does not prevent Assault Carrier arrival.
Infiltrate
A Battleship and Transport will fly around the target area, followed by an Overseer inserting in to the target city. This mission will cause the target country to leave XCOM immediately if successful. This mission requires a huge amount of resources from the aliens. Note that the final Overseer can only be detected if XCOM has the Hyperwave Decoder, so without one the country will appear to leave for no reason.
Retaliate
An Assault Carrier will fly to your main base or to one of your interceptor bases and immediately start an XCOM Base Defense mission or an Air Base Defense mission . The aliens can only field this mission if they have a lot of resources, and they will only do it if they consider XCOM a high threat (assaulting one of their bases will usually convince them of this, though sufficiently inconveniencing them before then will also do it).
Aliens usually send an Assault Carrier to main base assaults. If the aliens win a base defense it will damage resources and kill personnel - but it is not the end of the game, and can be recovered from. XCOM will lose the following resources on a failure:
- 450-550 cash
- 50-60 alloys
- 50-60 elerium
- 100-110 meld
- 20-30 scientists (capped to 1/3 of current staff)
- 20-30 engineers (capped to 1/3 of current staff)
- All alien captives
- Interceptor damage
For Air Base assaults, aliens will send an Overseer. The cost of failure of these missions is the destruction and/or severe damage of all stationed interceptors.
Oversee
An Overseer will fly around the target area, giving XCOM an opportunity to shoot down an Overseer.
Mission Table
At the beginning of each month, aliens plan all missions to be carried out that month based on their current resource level and perceived XCOM threat level.
| Threat 0 | Threat 1 | Threat 2 | Threat 3 | Threat 4 | |
| Resources 0 | 3.5 Abduction 3 Scout 3 Harvest |
3.5 Abduction 3 Scout 3 Harvest 0.5 Hunt |
3 Abduction 3 Scout 3 Harvest 1 Hunt |
2.5 Abduction 3 Scout 3 Harvest 1.5 Hunt 1 Bomb |
2 Abduction 3 Scout 3 Harvest 2 Hunt 2 Bomb |
| Resources 1 | 4.5 Abduction 1 Terror 3 Scout 3 Harvest |
4 Abduction 1 Terror 1 Research 3 Scout 2 Harvest 0.5 Hunt 0.5 Bomb |
3.5 Abduction 1 Terror 1 Research 3 Scout 2 Harvest 1 Hunt 1 Bomb |
3 Abduction 1 Terror 1 Research 3.5 Scout 2 Harvest 1.5 Hunt 1.5 Bomb |
2.5 Abduction 1 Terror 1 Research 3.5 Scout 2 Harvest 2 Hunt 2 Bomb |
| Resources 2 | 5 Abduction 1 Terror 4 Scout 2 Harvest |
5 Abduction 1 Terror 1 Research 4 Scout 2 Harvest 1 Hunt 1 Bomb |
4.5 Abduction 1 Terror 1 Research 4 Scout 2 Harvest 1 Hunt 1 Bomb |
4 Abduction 1 Terror 1 Research 5 Scout 2 Harvest 2 Hunt 2 Bomb |
3.5 Abduction 2 Terror 2 Research 5 Scout 1 Harvest 2 Hunt 2 Bomb |
| Resources 3 | 5 Abduction 1 Terror 4 Scout 2 Harvest 1 Bomb |
5 Abduction 1 Terror 1 Research 5 Scout 1 Harvest 1 Hunt 2 Bomb |
5 Abduction 1 Terror 2 Research 5 Scout 1 Harvest 2 Hunt 2 Bomb |
4.5 Abduction 2 Terror 2 Research 5 Scout 1 Harvest 3 Hunt 3 Bomb |
4 Abduction 2 Terror 2 Research 5 Scout 1 Harvest 3 Hunt 3 Bomb |
| Resources 4 | 5 Abduction 1 Terror 3 Research 5 Scout 4 Bomb 1 Infiltrate |
5 Abduction 1 Terror 3 Research 5 Scout 1 Hunt 3 Bomb 1 Infiltrate |
5 Abduction 1 Terror 3 Research 5 Scout 2 Hunt 3 Bomb 1 Infiltrate |
5 Abduction 2 Terror 3 Research 5 Scout 3 Hunt 3 Bomb 1 Infiltrate |
4.5 Abduction 2 Terror 3 Research 6 Scout 4 Hunt 3 Bomb |
See also
 Long War: Aliens
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Alien Life Forms • Alien Missions • Alien Deployment • Alien Artifacts • Alien Research • Alien Resources • UFOs • XCOM Threat |