Infiltrating missions require you to dispatch a squad several days before the mission so they can study the target and make plans. This is represented by an in-game "infiltration" value which accumulates as the squad spends more time at the mission location. The speed at which a squad infiltrates depends on its size, equipment and abilities, as well as the stage of liberation the mission's region is in for some missions. The final infiltration value, at the time you launch the mission, affects several aspects of tactical gameplay. This includes the quantity of enemies, their detection radius, and the delay before the Skyranger arrives for evac. Mission rewards and objective timers are not affected by infiltration.
The infiltration mechanic is the method by which most, but not all, missions are launched. The system is designed to provide a balance between the assignment of your haven personnel on intel gathering, the number of troops and equipment you bring on the mission, and the danger you will encounter on the mission.
When a mission is discovered you can deploy a squad, selecting soldiers and their loadout just like in the base game. Soldiers and equipment are unavailable while deployed to a mission. Once in place they will begin infiltrating. You can see their progress on the geoscape and you can click the mission bar to view details. From that screen you have the option to launch the mission immediately or to abort infiltration and recall your squad. The only penalty for aborting early is losing the squad's accumulated infiltration progress; you do not forfeit the mission. You can try to re-infiltrate with a newly selected squad if there is enough time left.
Most infiltration missions have a limited duration. You must launch the mission before it expires, but you don't have to watch the clock: if you have a squad deployed to infiltrate then the game will prompt you to launch or abort just before the mission expires. The time remaining for a mission is shown in the geoscape and in the top left of mission load-out screen. The load-out screen also displays the time to infiltrate, updated as you add or remove soldiers and equipment. This is how long the squad needs to reach 100% infiltration and eliminate all tactical penalties. If the squad's infiltration time is greater than the mission's time remaining then you won't be able to fully infiltrate. You can still deploy, but the mission will be more difficult. Infiltration can also be greater than 100%, up to 200% if the squad is allowed to remain infiltrating, which will make the mission easier.
A mission's expiration timer starts when it is created; the mission is not visible at this time. The local haven must collect enough intel to reveal the mission. Assigning more resistance members to the "intel" job can make missions considerably easier by discovering missions earlier and allowing more time to infiltrate. Most infiltration missions have a base duration of 18 days, which is randomized by a few days each time a mission is created. For more information on generating missions, see the Missions page.
To calculate the time a squad will take to reach 100% infiltration, the game uses 4 factors: Base Infiltration Time, Squad Size Factor, Squad Covertness Factor, and Liberation Factor. Infiltration can also be boosted, and liberating a region while a squad is infiltrating a mission in it will heavily affect their infiltration.
Base Infiltration Time
The base time each mission needs to be infiltrated changes depending on difficulty. For most missions the base times are:
|96 hours (4 days)||120 hours (5 days)||144 hours (6 days)||144 hours (6 days)|
However some Golden Path missions (Blacksite, Forge and Psi Gate) have double the base time of most missions. Other missions may have a flat modifier (positive or negative) depending on the activity, which is applied directly to the base time needed.
Squad Size Factor
The number of soldiers in a squad can affect significatively the hours needed for full infiltration:
The GTS project "Tactical Infiltrations" will reduce the Size Factors for 6 and 7 soldiers by 0.125, and "Large Unit Infiltrations" will reduce the Size Factors for higher numbers:
The Squad Size Factor has a minimum of 0.05 and a maximum of 10. The hours to full infiltration will be modified by the Base Infiltration Time multiplied by the Squad Size Factor - 1. A Squad Size Factor under 1 will remove hours instead.
When a squad of soldiers has been chosen to infiltrate a mission, the game will calculate the average covertness of the squad in this way:
- For each soldier, calculate two values from their equipment (including weapon upgrades): Covertness Value and Covertness Weight.
- Covertness Value is calculated by adding each piece of equipment's Covertness Value multiplied by their Covertness Weight. Empty spots have no value.
- Covertness Weight is calculated by adding each piece of equipment's Covertness Weight. Empty spots have 0.2 weight.
- If the soldier has leadership bonuses from the squad's officer, items or abilities that reduce individual infiltration times, apply each multiplier to their Covertness Value multiplicatively.
- To obtain each soldiers final covertness contribution: Covertness Value / Covertness Weight.
- For the squad's covertness, add all soldiers' final covertness, and for each of them that has an ability that reduces squad infiltration time (i.e. Infiltrator), apply each multiplier to the squad's covertness multiplicatively.
- Infiltrator has a 0.85 multiplier.
- Divide the squad's total covertness by the number of soldiers to obtain the average covertness.
The Squad Covertness Factor starts as 1 at 100 average covertness, and for each 100 difference in average covertness, the Factor will be increased or reduced by 0.67 (for example, 0.33 at 0 average covertness and 1.67 at 200 average covertness.
The Squad Covertness Factor has a minimum of 0.05 and a maximum of 10. If the Squad Size Factor is higher than 1, the Squad Covertness Factor will be applied to the Base Infiltration Time plus the hours the Squad Size Factor adds; if not, it will be applied only to the Base Infiltration Time. The hours to full infiltration will be modified by this time multiplied by the Squad Covertness Factor - 1. A Squad Covertness Factor under 1 will remove hours instead.
For some missions (Alien Facility Sabotage, Blacksite, Forge and Psi Gate), the stage of liberation that the region where the mission takes place is in will also affect infiltration times. This factor will always reduce infiltration times:
|Liberation Stage||No progress||Found a lead
(First Liberation mission unlocked)
|Rescue a Defector
|Hinder ADVENT Operations
|Destroy Network Tower
The hours to full infiltration will be modified by the Base Infiltration Time multiplied by the Liberation Factor - 1.
Boosting spends 25 Intel (30 on Legend) to further apply a factor to the time to full infiltration depending on difficulty:
The time to full infiltration will be divided by this factor after infiltration is boosted. This change applies retroactively to the calculation of infiltration %.
Final Infiltration Time
Adding together every factor will result in the time to reach 100% infiltration with that particular squad:
Base Infiltration Time = Base Hours (depending on difficulty) * 2 (if the mission is Blacksite, Forge or Psi Gate) + Flat Hours Modifier (depends on mission)
Squad Size Time = Base Infiltration Time * (Squad Size Factor - 1)
Squad Covertness Time = (Base Infiltration Time + Squad Size Time (if positive)) * (Squad Covertness Factor - 1)
Liberation Time (if mission is Sabotage Alien Facility, Blacksite, Forge or Psi Gate) = Base Infiltration Time * (Liberation Factor - 1)
Hours to 100% Infiltration = (Base Infiltration Time + Squad Size Time + Squad Covertness Time + Liberation Time) / Boost Factor (if intel is spent)
The hours to 100% infiltration cannot be lower than 12 or higher than 1296 (54 days). To calculate the infiltration value the squad has, divide the hours the squad has been infiltrating by the hours to 100% infiltration. The resulting percentage is the infiltration value shown on the mission screen, from 0% to 200%, which will have several effects on the tactical part of the mission.
If a region is liberated while squads are infiltrating missions in it, all infiltration values will be boosted by a flat 50% and the missions will be forced to begin immediately or be aborted.
Effects of Infiltration
An infiltration value of 100% gives no bonuses or penalties. Lower infiltration aids the aliens and higher infiltration aids XCOM, but these effects are not equal: the penalties for a low infiltration level are much worse than the bonuses for an excessive infiltration.
Each breakpoint corresponds to an increase or decrease in the effective Strength Level for the mission, respectively. This will directly change the number of enemies that spawn, which may affect the Enemy Activity Level reported. Being between two breakpoints gives you a percent chance to upgrade to the next breakpoint and reduce enemy activity level accordingly, with the chance increasing proportionally as you approach the next breakpoint. The change in activity level is also vaguely indicated in the "Enemy Readiness" tag when looking at the mission.
|Strength Level Change||+12||+11||+10||+9||+8||+7||+6||+5||+4||+3||+2||+1||0||-1||-2||-3|
For example, consider a mission with Very Light baseline enemy activity. Above 92% infiltration you are guaranteed to receive at worst Light enemy activity, with an increasing chance to get Very Light enemy activity as you approach 100% infiltration.
There are many more breakpoints below 100% than there are above it; missions will quickly become significantly more difficult at under 100% and you should try your best to reach this percentage. Similarly the difference between 150% and 200% is very small and may not be worth the squad strength cuts needed to attain 200%.
Golden Path missions (Blacksite, Forge, Psi Gate, ) are not affected by this modifier. ADVENT Network Tower and Alien Fortress are affected by this modifier but only for overinfiltration (as they require at least 100% infiltration to launch).
Skyranger Evac Delay
The Evac Delay timer can be modified by the infiltration value, among other things. As soon as the infiltration value indicated in the breakpoint is reached, the corresponding Evac Delay modifier will be active. For more information on Skyranger Evac time, see Skyranger Evac Mechanics.
|Evac Delay Turns||+3||+2||+1||0||-1||-2|
Enemy Reflex Actions
The chance of enemies taking a reflex action when they're activated on their turn can be modified by the infiltration value, depending on difficulty.
- This is the base chance for enemies to take a reflex action:
- Each point of infiltration over 100% will decrease the reflex chance by this amount:
- Each point of infiltration under 100% will increase the reflex chance by this amount:
On Troop Column Ambushes, Supply Raids, or landed UFO missions, a minimum of 100% infiltration value is needed for the squad to start the mission in concealment.
Enemy Detection Range
The radius at which enemies can detect soldiers in concealment is affected by the infiltration value in different ways depending on difficulty.
- Above 100%, the detection radius of enemies will be reduced linearly from 100% of its default value to the minimum percentage at 200%:
- Below 100%, the detection radius of enemies will be increased linearly from 100% of its default value to the maximum percentage at 0%:
Disguised Faceless will not be affected by this. For more information on enemy detection, see Detection Radius Mechanics.
Low infiltration values will advance the reinforcement queue from the start, meaning the first reinforcements spawned will be stronger. As soon as the infiltration value indicated in the breakpoint is reached, the corresponding reinforcement queue modifier will be active:
|Queue Spots Advanced||5||4||3||2||1||0|
For more information on enemy reinforcements, see Reinforcements.
|Other Weapon Upgrades||0||0|
|Advanced Psi Amp||40||0.5|
|Alien Psi Amp||30||0.5|