Alien Missions (Long War)

Overview

During the long war against the alien threat, the skies are also part of the battlespace. Aliens will dispatch sorties of UFOs to further their goals during the war, and XCOM may respond in kind by sending out interceptors and the Skyranger to foil their missions in the air or on the ground. In other words, an alien mission always starts with an UFO sortie.

There are eight types of regular alien missions scheduled on a monthly basis. The type of each mission is determined by the resources the aliens have, and how threatening XCOM is perceived to be. There are also two special mission types that occur irregularly. All ten mission types are listed and discussed below, followed by a table detailing the scheduling of the regular missions.

The aliens' choice of UFOs is limited by their research and resources, with the actual ship sent on a mission being chosen randomly - with equal probability for each - from the available pool. For example, if the aliens have little resources, then they will randomly send either a Scout or Raider for research; if they have plentiful resources, however, then the large Abductor and Terror Ship will be added to the pool for the same mission. Any damage and casualties sustained by the UFOs will cut into the aliens’ resources, likely limiting their options in the following month.

The aliens like to focus on generating panic in countries and continents near their established bases. They prioritize any such countries with the highest panic, in order to push them over the edge and induce them to withdraw from the council.

Mission Scheduling

All missions are computed and scheduled at the beginning of each calendar month. They determine what missions to do, which countries to do them in, what day and time to do them in, and which UFOs to use. Dynamic War: changes mission scheduling from vanilla to occur more or less frequently than once per month in order to produce more or less missions, depending on the INI scaling value used.

• Type and Quantity: Which missions to do are largely determined according to a table, based on resource levels and perceived XCOM threat (see Mission Occurrences, below).
• Target: Which countries to do them in are determined semi-randomly, with each mission type having its own logic. In general, all missions except Bomb and Harvest will either target countries with satellite coverage and allow you to shoot them down, or generate a mission that gives you an opportunity to deploy a ground force against them. As a result, additional satellite coverage doesn't usually meaningfully change your monthly missions, so don't avoid expanding to additional continents if you have an air force that can handle it out of fear that your ground force will be overburdened. And as discussed before, missions that focus on increasing panic tend to target specific countries each month, hereafter referred to as Strategic Target.
• Date: What day to do them in each month is largely random and based on mission type, though most mission types tend not to occur in the last few days of each month. If a date range is given, each day in that range is equally likely, and then a random time in that day is selected from among discrete half hour increments. As a result of random chance, missions can be scheduled back-to-back or they can be spread out along the length of a month. Always keep a healthy barracks and interceptor bay ready for consecutive ground or air sorties.

UFOs Used

While some missions have a predetermined UFO or set of UFOs that can appear, many missions select one randomly. Which UFOs are deployed may depend on up to four factors: the mission type in question, the level of resources the aliens have, and the level of research the aliens have, and randomness. All of this is evaluated at the time the mission is scheduled (beginning of the month for standard campaigns).

Specifically, many mission types have its own pool of UFOs that it can field, with each UFO in the pool equally likely to be randomly selected. As the aliens gain more resources, additional UFOs can be added to the pool (again, depending on the mission type). And as the aliens gain more research, the resource thresholds required to add these additional UFOs to the pool are decreased. Specifically:

If Alien Research > 0, new types require 100% of their base required resources.

If Alien Research > 360, new types are possible at 72% of required resources.

If Alien Research > 720, new types are possible at 40% of required resources.

Missions themselves do not require the aliens to spend resources to run if left unchallenged, but shooting down or damaging the UFOs conducting them does cost the aliens resources to repair or replace the UFOs.

Mission Types

Individual UFO Sortie

Individual UFO sorties are missions conducted by a solitary UFO. Shooting down the UFO (or assaulting it if it lands) is always sufficient to prevent the mission from succeeding. Dealing damage to the UFO sometimes, but not always, can affect the outcome.

Scout

Target: Random country with satellite coverage

Date: 1st to 27th of the month

UFO Signature: Low

Flight Pattern: Air patrol

Result: Spawns a bonus free Hunt mission

Failure Condition: Shoot down UFO; also, randomly due to damage, country defense, or bad luck

UFO Pool:

• Scout (Small): Always in pool
• Raider (Medium): Aliens must have > 50 / 36 / 20 resources
• Destroyer (Medium): Aliens must have > 225 / 162 / 90 resources
• Battleship (Very Large): Aliens must have > 300 / 216 / 120 resources

Not to be confused with the Scout, a type of UFO.

A UFO will fly low and around the target country, attempting to confirm the existence of XCOM satellites. Successful scouting missions will be automatically 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 depending on how tough the UFO is; if the UFO sent to scout is tough (e.g. an early game Raider), you could gamble that the UFO being sent to hunt will be weak (i.e. a Fighter). Conversely, you could be punished if a stronger UFO (i.e. a Destroyer) follows up instead. Fortunately, Hunt missions automatically fail if the UFO has less than 50% of its HP remaining, so it's slightly easier to stop then Scout missions even if you can't shoot it down.

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: UFO Damage Taken % - this means XCOM can commit less and gamble on merely damaging the UFO, though you can only guarantee failure by downing the UFO.
• Defended: (Country Defense / 2)% - the shield representing a country's defense is shown in the Situation Room and is improved by fulfilling their requests; the maximum is a 50% failure chance with 100% Country Defense.
• Damned: (60 - Alien Research / 15)% - this means when the aliens have 900 research points, an unfettered scouting mission will always succeed.

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. So long as the aliens don't have enough resources to regularly field a battleship, Scout missions will comprise a sizeable proportion of your monthly income.

Hunt

Target: Alien Bases with satellites over them, Strategic Targets with satellites, or just countries with satellites

Date: 1st through 27th of the month

UFO Signature: High w/ purple strobe effect

Flight Pattern: Air patrol

Result: Destroys the satellite

Failure Condition: Shoot down, or randomly due to damage

UFO Pool:

• Fighter (Small): Always in pool
• Raider (Medium): Aliens must have > 100 / 72 / 40 resources
• Destroyer (Medium): Aliens must have > 100 / 72 / 40 resources & > 75 alien research
• Battleship (Very Large): Aliens must have > 225 / 162 / 90 resources & > 75 alien research

A UFO will fly at high altitude over a satellite-covered country, seeking to destroy the satellite. A Scout mission, if successful, is always immediately followed up by a Hunt mission, with a potentially different UFO. Thus, if a Scout mission presents you with a tougher UFO than you can handle, you can gamble on the followup Hunt mission being easier. Likewise, fail to shoot down an easy Scout mission and you could get a much tougher Hunt mission.

Successful hunts will destroy the satellite in question, setting XCOM back about §200 in replacement costs and removing the associated country satellite bonus (and continent bonus, if applicable). 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 proportional to twice the damage dealt to the UFO, and thus dealing 50% or more of its HP in damage leading to an automatic failure. Pertinent to this, 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 if need be, preventing further risks while stopping the hunt mission. That said, a downed UFO provides a hefty quantity of resources, so try to down it if at all possible, as you get nothing but lengthy repair times when you only damage it.

In addition to the replacement costs, the loss of a satellite imposes a hidden but potentially far more important cost as well: while the satellite coverage is down, all Research, Harvest, and Bomb missions that were otherwise scheduled for that target country automatically succeed, and any Scout or Hunt missions that were scheduled to target that country will be skipped, and XCOM is robbed of the opportunity to recover materials from them. Research, Scout, and Hunt missions account for a very large portion of your monthly income in a campaign, as they normally always target satellite-controlled countries (regardless of how many satellites you have or where they are located). Particularly in the early months, when you don't have much satellite coverage and the vast majority of such missions are concentrated on 1-3 countries, the loss of a single such countries satellite can set you back a ton of resources and XP for your soldiers.

However, note that the aliens intelligence on your satellites is abstracted somewhat, and Hunt missions can randomly spawn without immediately being preceded by a successful Scout mission. These "Direct" Hunt missions have a specific targeting priority:

1. Any satellite over an alien base
2. Strategic Target (if it has a satellite over it)
3. Random country with a satellite

Direct Hunt missions can only be scheduled if XCOM is seen as a threat (2+ threat) and depending on the amount of resources the aliens have this may be only a 50% chance to see one at all. The more threatening XCOM is and the more resources the aliens have, the more direct hunt missions are sent, up to a maximum of four per month.

Research

Target: Random country with satellite coverage

Date: 2nd through 27th of the month

UFO Signature: NOE

Flight Pattern: Landing

Outcome: (If UFO takes off after landing) awards research to aliens

Failure Condition: Shoot down or assault landed UFO (unaffected by damage)

UFO Pool:

• Scout (Small): Always in pool; generates +3 research for the aliens
• Raider (Medium): Aliens must have > 75 / 54 / 30 resources; generates +5 research for the aliens
• Abductor (Large): Aliens must have > 125 / 90 / 50 resources; generates +8 research for the aliens
• Terror Ship (Large): Aliens must have > 250 / 180 / 100 resources; generates +10 research for the aliens
• Assault Carrier (Very Large): Aliens must have > 300 / 216 / 120 resources; generates +?? research for the aliens

A UFO will fly NOE, land for a while, and then fly off. This is a recon-in-force mission conducted against XCOM operations. They are always conducted within regions that XCOM maintains a Satellite presence, and mission will grant the aliens research if successful, which will slowly but permanently increase the capabilities of their ground troops and UFOs; the quantity of research earned is directly proportional to the quality and size of the UFO used to conduct them.

To stop the aliens, simply allow the UFO in question to land, and assault it; you'll prevent them from gaining any research if you manage to succeed, and you'll make out with a large amount of resources from the intact UFO. Shooting down the UFO is not necessary and even counterproductive, as it reduces the number of corpses, materials, and XP you can harvest. That said, when assaulting UFOs that have successfully landed, always be wary of trapped UFOs: such UFOs can have massive increases in the number of aliens that crew them, and the chance is roughly proportional to the amount of UFOs XCOM has shot down so far this month. Shooting down the UFO does stop it from being a trap, so it's an option, but you're robbing yourself of lots of resources, corpses, and kill XP by doing so.

If the aliens have no resources (<50 resources) to spare, the aliens will never schedule research missions; conversely, if they already have too many resources (200+ resources), then the maximum amount of research missions will be scheduled (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 carry out fewer 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.

Harvest

Target: Semi-random country (priority: unprotected by satellites)

Date: 1st to 26th of the month

UFO Signature: NOE

Flight Pattern: Landing

Outcome: (If UFO takes off after landing) awards resources to aliens

Failure Condition: Shoot down or assault UFO (unaffected by damage)

UFO Pool:

• Transport (Large): always in pool; generates +37-40 resources for the aliens
• Harvester (Large): Aliens must have > 75 resources; generates +27-30 resources for the aliens
• Raider (Medium): Aliens must have > 125 resources; generates +17-20 resources for the aliens
• Scout (Small): Aliens must have > 225 resources; generates +10-14 resources for the aliens

A UFO will fly NOE, land for a while collecting resources, and then fly off. An unimpeded harvest grants the aliens resources, which will allow the aliens to field more UFO sorties per month as well as use greater quality UFOs.

If you manage to detect the UFO, you can assault it after it lands, preventing the aliens from obtaining the resources and bringing home a large haul of materials, more than you would for a crashed UFO. That said, always be wary of trapped UFOs: such UFOs can have massive increases in the number of aliens that crew them, proportional to the amount of UFOs XCOM has shot down so far this month. Shooting down the UFO does stop it from being a trap, so it's an option, but you're robbing yourself of lots of resources, corpses, and kill XP by doing so.

Harvest missions are one of the few UFO missions in the game (alongside Bombing missions) that can be fully completed without XCOMs knowledge or awareness, and thus XCOM may not have an opportunity to prevent them from succeeding. In addition to picking the country entirely at random, they also tend to avoid locations in which XCOM has satellite coverage. Specifically, if the targeted country has a satellite, there is a 10% chance for every 2 full points of of threat, max 40% (i.e. 0% at 0-1, 10% at 2-3, 20% at 4-5, 30% at 6-7, and 40% at 8+), that the aliens will re-roll the target country to one without satellite coverage, paying a flat 5 resources 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, and more opportunities for you to target these craft and turn the aliens' attempts at resource-gathering into one of your own.

Note also that the UFO pool for harvest missions becomes less threatening the more resources the aliens, and isn't affected by higher Alien Research; this is the opposite of all other missions with random UFO pools. As a result, it's entirely possible (albeit unlikely) to see a Transport carrying 30+ aliens in the first few months; it's also entirely possible to defeat this mission, even in March, but attempting this isn't recommended for newer players - it will be very long, extremely difficult and potentially require some degree of luck and/or cheese tactics. You could also encounter some Harvest missions in the midgame, but again it is less likely as you will likely be threatening enough for the aliens to try and reroll, though completing landed Transports and Harvesters is entirely possible and recommended if you want to snowball. Only when you've got the majority of the globe covered should you expect to be able to routinely disrupt alien Harvest missions, but at that point the aliens will have alien bases and a monthly free minimum amount of resources to sustain them.

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 (<50 resources), then a maximum amount of harvest mission is attempted (three per month); if they have too many resources (200+), then no harvest will occur. 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.

Bomb

Target: Strategic Target

Date: 2nd to 27th of the month

UFO Signature: NOE w/ purple strobe effect

Flight Pattern: Air patrol

Outcome: Generates up to 10 panic in target country (reduced by % damage dealt)

Failure Condition: Shoot down UFO

UFO Pool:

• Fighter: Always in pool
• Destroyer: Aliens must have > 75 / 54 / 30 resources
• Battleship: Aliens must have > 175 / 126 / 70 resources

A UFO will fly NOE around the target area bombing civilian targets, generating up to 10 panic in the target country 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 air raid generates 8 panic in the country raided, with damage to the UFO reducing the panic proportionally; half-damaged means half panic, and a shoot down means no panic. An additional 2 panic is added if the UFO is undamaged.

Bombing missions, like Harvest missions, are one of the few UFO missions in the game that can be completed without XCOMs knowledge and awareness, and thus XCOM may not have an opportunity to prevent them from succeeding. Bombing missions pick countries at random, and without satellite coverage over a country, XCOM will not be able to see and engage the UFO. Successful bombing missions will be reported in the scrolling news ticker of the Situation Room, however, alerting you to the outcome even if you lack the satellite coverage to intercede. In the early and mid game, there will likely be a few bombing missions taking place in countries you have no satellite presence in each month, and so expanding your satellite coverage can help you earn some additional resources and soldier XP from the shoot downs and prevent panic from spreading.

The aliens will send out more bombing missions if they have spare resource and perceive XCOM as a threat; both more resources and more threat will cause the aliens to engage in more bombing campaigns. 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

Target: Random Country that isn't the target of a terror mission this month

Date: See chart, below

UFO Signature: NOE

Flight Pattern: Landing

Outcome: (UFO arrives at destination) spawns an Abduction mission

Failure Condition: Shoot down UFO before landing (unaffected by damage)

UFO: Abductor

An Abductor will fly NOE to the target area and generate an Abduction site, giving you an opportunity to defeat the alien ground forces in exchange for a cash bonus from the Council. 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.

Abductions are generally scheduled so that they are roughly evenly spaced throughout the month and with at least 1 day in between consecutive Abductions, but this depends on the number of Abductions scheduled:

Abduction Scheduling
Per Month	Date for each Abduction
	1st	2nd	3rd	4th	5th
2	1st - 14th	16th - 29th
3	1st - 9th	11th - 19th	21st - 29th
4	1st - 6th	8th - 13th	15th - 20th	22nd - 27th
5	1st - 5th	7th - 11th	13th - 17th	19th - 23rd	25th - 29th

The target of an abduction is always a random country remaining within the XCOM project, and the aliens avoid selecting countries which also have a terror attack scheduled that month.

The true motivations behind these abductions are not made clear, and may tie in to the aliens overall reasons for the invasion; 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 compared to Terror Missions if it's about strategic warfare. As these sorties always spawn an Abduction mission, you don't need to worry about satellite coverage or shooting the UFO down, since you'll be given an option to send a ground team over whenever one occurs. Treat the mission as a good way to get some cash, corpses, and XP.

In many ways abduction is the least aggressive mission type; perhaps due to this, the aliens will scale back on abduction attempts somewhat if they feel threatened by XCOM, and especially if they have low resources (<50), down to a minimum of 2 per month. Conversely, moderate resource values (100+) can allow them to hit a cap of up to 5 Abductions per month at low threat (0-1), and high resources (200+) can allow them to maintain 4-5 Abductions even in the face of a highly threatening XCOM (8+).

Command Overwatch

Target: Random Country

Date: 5th, 15th, and 25th of the month

UFO Signature: Low w/ Blue Colored UFO

Flight Pattern: Air Patrol

UFO: Overseer

This is a special mission. An Overseer will fly low around the target area. This mission does not do anything for the aliens, and its only purpose is to allow XCOM the opportunity to shoot down an Overseer to continue the story. It only technically begins spawning after the Hyperwave Relay (Long War) is first constructed, as Overseers are invisible to XCOM without it.

Retaliation (Air Base)

Target: Random Continental Interceptor Base with a Firestorm

Date: 1st to 26th of the month

UFO Signature: NOE

Flight Pattern: Landing

Outcome: (UFO arrives at destination) spawns an Air Base defense mission.

Failure Condition: Shoot down Overseer (unaffected by damage)

UFO: Overseer

A long-war original addition. The aliens will send an Overseer to a random continental interceptor base that has a Firestorm, spawning an Air Base defense mission on arrival. Being an Overseer, it is invisible until the Hyperwave Relay is constructed.

Air Base defenses cannot occur unless XCOM has at least one Firestorm interceptor, following which one Air Base Defense has a 50% chance to trigger every month that Aliens have 100+ resources and 4+ threat, so long as the Aliens do not also meet the threshold for progression towards an HQ base defense (i.e. has fewer than either 8 threat or 150 resources). The cost of failure of these missions is the destruction and/or severe damage of all stationed interceptors.

Multiple UFO Sortie

Multiple UFO sorties are individual missions that involve multiple UFOs working in concert. To prevent the mission from succeeding, a specific UFO must be shot down, though the other UFOs may cause problems in the mean time.

Terrorize

Target: Strategic Target or Random

Date: 1st through 23rd of the month

Sortie Signature: Terror Ship (Air Patrol) + Assault Carrier (Landing)

Outcome: (Assault Carrier arrives at destination) spawns an Terror mission.

Failure Condition: Shoot down Assault Carrier (unaffected by damage)

This is a double sortie mission: At first, a Terror Ship will fly NOE and hover over the target nation scouting and planning for the actual mission (and giving XCOM some advanced warning). Later, an Assault Carrier will fly NOE to the target area and finally generate a Terror site. Fortunately, you don't need satellite coverage to deploy to the terror site and disrupt the mission. On the other hand, anyone with satellite coverage and interested in stopping the mission will have plenty of advanced notice, though actually executing that is a different matter entirely.

The target for the first terror attack scheduled is usually a Strategic Target, unless the aliens have 200+ resources in which case it is a random country. If there is a second terror attack scheduled for the month, the target is also a random country.

Terror missions increase panic by +3 in the targeted country/+1 continent-wide per civilian killed, so these missions are always highly likely to see at least some benefit for the aliens. Losing or ignoring the mission, however, causes the enemy to follow up with an automatic Infiltration mission 5 to 12 days later which will cause the country to leave the XCOM project. It also increases panic continent-wide by 20.

There are only two ways to completely foil this kind of terrorism: by saving every single civilian during the engagement, or by shooting down the Assault Carrier before it lands. Neither of these scenarios are likely to happen most of the time, and will probably be cost prohibitive to even try. Only an exceptionally advanced and exceedingly experienced XCOM can pull either option off. Otherwise the best a commander can do is to minimize the damage and make up for it elsewhere: countries that leave the XCOM project due to panic or failed terror missions can eventually be returned to the fold if XCOM manages to locate and assault the alien base installed within the country.

Terror missions are quite costly for the aliens as well. In fact, they cannot even afford it when they have the minimal level of resources (<50 resources). Otherwise they will always conduct one such mission per month, at the very least. In the presence of a threatening XCOM (6+ threat), the aliens will try to scrounge up enough resource to deploy a second terror mission per month, at the expense of other missions. This means unfortunate commanders may see four terror missions near the turn of the month, as the scheduled missions could be stacked at the end of the current month and beginning of the next by random chance.

Shooting down the forward scouting Terror Ship doesn't actually hinder the scheduled mission in any way. It's not that much easier to do than shooting down an Assault Carrier, so don't attempt it without heavy investment in the air game. But succeeding forces the aliens to pay dearly by accruing resource costs for each such Terror attack they perform. In addition, it will grant XCOM a lot of looted resource and battlefield experience if the downed Terror Ship is successfully raided. It may not stop the looming terror attack, but it can be used as an extra source of resources and income.

Infiltrate

Target: Strategic Target

Date: 5th to 12th of the month

Sortie Signature: Transport (Air Patrol) + Battleship (Air Patrol) + Overseer (Landing)

Outcome: (Overseer arrives at destination) country leaves the XCOM project and an Alien Base is Constructed.

Failure Condition: Shoot down Overseer (unaffected by damage)

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, and the aliens will construct a base in the target country. This base can be assaulted by XCOM, which in addition to providing large amounts of resources for the war effort will allow the country in question to return to XCOM and resume its financial and materiel support of the XCOM project. Note that the Overseer can only be detected if XCOM has the Hyperwave Relay, so without one the country will appear to leave for no reason.

The aliens will always perform this at least once in a campaign, in the very first month (constructing the plot-necessary guaranteed minimum of at least one Alien Base for you to assault in order to progress the main story missions); they will always select a random country in a continent that is not your starting country. Following the first month, this is a very expensive operation for the aliens, and as such they can only afford it if they have maximal resources (200+ resources), and only when they're not too distracted dealing with XCOM (<8 threat). Furthermore, it targets high panic countries, so it's usually not much worse for you than a terror mission if it triggers.

Retaliation (XCOM HQ)

Target: XCOM HQ

Sortie Signature: Battleship (Hunt) + Assault Carrier (Landing)

Date:

Battleship: 2nd to 7th of the month

Assault Carrier: 8th to 25th of the month

Outcome: (Assault Carrier arrives at destination) spawns an XCOM HQ defense mission

Failure Condition: Shoot down landing craft (unaffected by damage)

This is a special mission. The aliens will send a Battleship to shoot down the satellite over your headquarters near the beginning of the month, and then at some point an Assault Carrier will fly to your main base and immediately start an XCOM Base Defense mission.

This is an incredibly difficult mission that pits a limited quantity of semi-random soldiers against a rather large enemy force. Fortunately, if you can get your satellite back up you can spot the main assault group coming and prepare, such as cancelling any Gene Mods and Psionic training that soldiers are undergoing. You could also put down a rush job for extra weapons and armor, or the Foundry projects that boost blue shirts if your satellite goes down suddenly to a Battleship and cancel anything that doesn't make it in time.

The aliens can only field such missions if they have a lot of resources and they consider XCOM a high threat; specifically, for every 3 months (not necessarily in a row) that the aliens are at the maximum threat (8+) and at least the second highest resource (150+) tiers, an XCOM Base Defense will spawn. Additionally, if XCOM has yet to encounter a base defense yet in the campaign, one will always occur exactly one year into the campaign, some time in March of the second year (if this occurs, the counter is reset, so you won't see another until the requisite three months have passed).

Mission Occurrences

At the beginning of each calendar month, aliens plan all missions to be carried out that month based on their current resource level and perceived XCOM threat level. Most monthly missions are directly dependent upon these two variables, with two exceptions: Command Overwatch and Retaliation (see below). Note that if an Alien Base was raided in the previous month, threat is automatically treated as being in the highest tier (8+) for the purposes of mission scheduling.

Common Missions

The following table indicates which missions the aliens will plan to run at the beginning of each month, given the aliens current Resource counter at the beginning of the month and the Threat counter XCOM's anti-UFO operations accrued last month. Resources and Threat are divided into 5 "tiers" each, and the intersection between those two levels determines the monthly missions.

If a range is provided for the number of missions run, i.e. 3-4 Abductions, each possibility (either 3 or 4) is equally likely.

Resources	Threat
	0-1	2-3	4-5	6-7	8+
50 or less	3-4 Abduction 3 Scout 3 Harvest	3-4 Abduction 3 Scout 3 Harvest 0-1 Hunt	3 Abduction 3 Scout 3 Harvest 1 Hunt	2-3 Abduction 3 Scout 3 Harvest 1-2 Hunt 1 Bomb	2 Abduction 3 Scout 3 Harvest 2 Hunt 2 Bomb
50-99	4-5 Abduction 1 Terror 3 Scout 3 Harvest	4 Abduction 1 Terror 1 Research 3 Scout 2 Harvest 0-1 Hunt 0-1 Bomb	3-4 Abduction 1 Terror 1 Research 3 Scout 2 Harvest 1 Hunt 1 Bomb	3 Abduction 1 Terror 1 Research 3-4 Scout 2 Harvest 1-2 Hunt 1-2 Bomb	2-3 Abduction 1 Terror 1 Research 3-4 Scout 2 Harvest 2 Hunt 2 Bomb
100-149	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	3-4 Abduction 2 Terror 2 Research 5 Scout 1 Harvest 2 Hunt 2 Bomb
150-199	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
200+	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

Retaliation Mission

Once three (3) months have passed (not necessarily in a row) in which the aliens have both 150+ resources and 8+ threat, a Retaliation mission targeting XCOM headquarters will be generated in the month. Furthermore, if no XCOM Base Defense mission has occurred yet in the campaign so far, one will automatically happen in March of the 2nd year.

Strikes against XCOM's continental interceptor bases occur more frequently. If the above condition for progress towards a strike against XCOM HQ is not met, there is a 50% chance for the aliens to strike a random continents air base with a Firestorm in it each month starting at 100+ resources and 4+ threat. XCOM HQ is safe from such attacks, however, so the aliens will not target any Firestorms located in your home continent, nor can these missions spawn when XCOM has no Firestorms to target.

Command Overwatch Mission

Command Overwatch occurs in one random country anywhere on the globe, 3 times per month, starting when the Hyperwave Relay is first built. The missions take place on the 5th, 15th, and 25th of the month.