UFO Typesaliens range in size and on their individual missions. The exact aliens each craft carry can also vary considerably due to timeline, story progression and difficulty level.
|Type||Size||Missions (First Appearance/Marathon)||Tactical Maps|
| Small Scout
||Small|| Scout Target (March)
Harvest Live Specimens (April)
| Small Scout Badlands|
Small Scout Dirt Road
Small Scout Marshlands
Small Scout Quagmire
Small Scout Farm
Small Scout Nuked City
Small Scout Roadhouse
Small Scout River
Small Scout River Valley
| Large Scout
||Medium|| Scout Target (April)
Harvest Live Specimens (May/June)
Destroy Satellite (March1)
|Large Scout Deep Woods|
Large Scout Forest Trench
Large Scout Stonewall
Large Scout The Barrens
Large Scout City
Large Scout Creepy Forest
Large Scout Hillside
| Overseer UFO
||Medium||Final Preparations (after Hyperwave Relay is built)||Overseer Deep Woods|
Overseer Forest Trench
Overseer Stone Wall
Overseer The Barrens
||Large|| Scout Target (May/June)
Harvest Live Specimens (July/October)
Abduct Specimens (March2)
Abductor Scorched Earth
Abductor Farm Outskirts
Abductor Winding Stream
| Supply Barge
||Large|| Scout Target (August/December)
Harvest Live Specimens (September/February)
|Supply Ship Overlook A|
Supply Ship Wildfire
Supply Ship Forest Grove
Supply Ship Rocky Gorge
||Very Large|| Scout Target (October/April)
Terrorize Populace (April2)
Destroy Satellite (See1)
| Battleship 01|
|1The Large Scout is replaced by the Battleship in June (Easy/Normal difficulty levels), May (Classic) or April (Impossible)|
2 These UFOs cannot be detected
For Temple Ship details see the Storyline page (massive spoilers!).
The amount of aliens on a crashed UFO mission will always be lesser than on a UFO that Landed UFO on its own.
UFOs came on a variety of types and some will only perform specific missions, with their generation determined by the A.I. game objectives. Each mission will be generated by the A.I. and then a UFO will be assigned, either predetermined or random. It is possible to see the UFO's specific objectives after building the Hyperwave Relay in HQ.
Each month the A.I. will create several missions in order to achieve the following objectives:
|Objective/Mission||UFO type||UFO detection||UFO Appearance 4|
|Harvest Live Specimens||Any UFO, except the Overseer||Yes||UFO can appear on days 2-16 or 9-23|
|Scout Target||Any UFO, except the Overseer||Yes||UFO can appear on days 9-10 or 16-17|
|Destroy Satellite||Large Scout or Battleship||Yes||2nd UFO appears up to 5 days after 1st UFO is ignored.|
|Abduct Specimens||Abductor||No1||1st Abductions: can happen on days 1 to 8; 2nd Abductions: can happen on days 11 to 25|
|Terrorize Populace||Battleship||No1||Can appear on days 13-27|
|Final Preparations||Overseer||Yes2||Can appear on days 2-8, 12-18 or 22-28|
|Reconaissance||Small Scout||Yes||1st UFO detected. Will appear on days 5 to 15|
|Target Reconnaissance||None3||?||Never generated|
| 1 By changing the value of ShowUFOSonMission from 0 to 1 on the DefaultGameCore.ini file it is possible to detect these UFOs.|
2 Only after Hyperwave Relay is built on HQ.
To achieve the previous objectives, the Aliens (a.k.a. A.I.) make a monthly plan of missions that is checked and updated every half hour of game time. This includes generating a country list to determine possible Abductions targets, along with any countries marked for a Terror Site. The aliens schedule also includes all the missions where UFOs can be detected, or ones taking part in Harvest Live Specimens, Scout Target or Final Preparations missions, and finally, any future Council missions.
Detected UFOs can be conducting 4 types of UFOs: Scout Target, Destroy Satellite, Harvest Live Specimens, and Final Preparations.
- Each month there's a limit of 2 UFOs being detected either landed (Harvest Live Specimens mission) or flying (Scout Target or Final Preparations missions), more UFOs can appear in case a Destroy Satellite UFO mission is generated but there's a maximum of 2 UFO ground missions. The UFO type will never be the one of the last mission.
- Before the Alien Base assault, a 2nd UFO can be detected only in April and May (April to June with Marathon). After the Alien Base is assaulted, a 2nd UFO can be detected every month.
- If any Harvest Live Specimens or Scout Target missions are completely ignored the aliens will send quickly a Large Scout/Battleship on a Destroy Satellite mission. If the first mission is ground assaulted or intercepted, regardless of the final result, the 2nd mission will not be generated.
- If the last mission has been a Crashed UFO, there's a 66% chance that a UFO will appear on a Scout Target mission. Otherwise it will be a Landed UFO mission. This value is defined on the UFO_INTERCEPTION_PCT setting at DefaultGameCore.ini.
- The function used is ChooseUFOMission on XGStrategyAI at XComStrategyGame.upk
- The game will make a pool of available UFOs for either the Harvest or Scout Target missions, adding new types each month and randomly selecting a type for the mission. The exceptions are in the two first months, where the aliens will send predetermined UFO types on Scout Target missions (Small Scout in March & Large Scout in April).
UFO Flight Modes
Detected UFOs can have several flight modes, depending on their mission:
- Arrival - there are 2 difference possible approaches, although the UFO can't be detected. UFO's speed will be 50% of max.
- SpendTime - UFO loiters in a determined area, flying time usually determined to be 4 hours, with a speed of 75%
- FlyOver - heads towards a specific location at 75% speed
- Landing - heads towards its target landing area, speed is 20%
- Departure - towards a random location, UFO's speed will be 50% of max (needs checking since it appears otherwise, that the UFO accelerates when compared to FlyOver speed)
- Liftoff - UFO can't be detected, speed incremented over max
A UFO's flight plan will consist of several of these modes, depending on its mission. A Flying UFO has 5 modes: Arrival, SpendTime (usually about 4 hours), FlyOver, Departure and Liftoff. However, once the UFO is intercepted but not shot down it will immediately switch from SpendTime to Flyover to prepare itself to leave the Earth's atmosphere.
- Before the Alien Base mission, there will be 2 Abductions each month, regardless if there's 3 or more countries left in the Council without a satellite.
- After the Alien Base is assaulted it can be none or up to 2 monthly missions, depending if there's still 3 or more countries remaining on the Council without satellites.
- The aliens will target any countries still in the Council that don't have a satellite deployed and avoid any country already marked for a Terror Site during the month.
- The number of countries with abductions is 3, but it can be less, depending on the number of countries without a satellite, if the Alien Base hasn't been assaulted yet.
- Each country marked for Abductions has a Large Scout sent first for reconnaissance and afterwards an Abductor that carries the mission. These UFOs can only be detected and shot down if the ShowUFOSonMission value on the DefaultGameCore.ini file is changed. If that happens, the Abduction mission over that country will not take place.
- It is also possible to mod the AI so that it will choose countries with satellites as Abduction targets.
- Before the Alien Base mission, there's 1 Terror Site every even month (April, June, etc.). After the base is destroyed, it takes place every month.
- There's a 75% chance that the aliens will choose to terrorize the most panicked country. If not, the aliens will prioritize countries in continents with the most panic levels.
- The targeted country will also be removed from any Abduction missions that take place.
- This mission is consists of undetected 2 Battleships on a Terrorize Populace mission, the first one for scouting, the second to carry the actual mission. If they are detected (possible through changing the ShowUFOSonMission value) and the 2nd Battleship is shot down the Terror mission will not take place.
- The UFO will roam around in the region it is patrolling. If left unattended (no interception attempt is made), it will trigger the arrival of a UFO on Destroy a Satellite mission in the following several days.
- This mission is initially performed by the Small Scout, and at certain month the aliens will add another type to be randomly chosen when the mission is generated: Large Scout (April), Abductor (May), Supply Barge (August) and October (Battleship).
- Notice that the following UFO will be a larger-class UFO. This can be used to your advantage: by letting scouting UFO get away on purpose, you are increasing amount of loot you can get from a successful crash recovery mission. However, be prepared to take down the larger UFO and win a harder tactical mission.
Harvest Live Specimens
- All landed UFO missions will be of this type and it can be taken by any UFO, from Small Scouts to Supply Barges, with the exception of the Battleship. Sending a squad to assault the craft will result in a Landed UFO ground mission.
- If this mission is ignored (if no tactical mission is launched, regardless of a victory or a defeat) it will later generate a UFO on a Destroy Target mission.
This mission can only happen if you ignore an airborne UFO or landed UFO, and is a good way of getting more Battleships in order to harvest more Fusion Cores for Blaster Launcher production. If the UFO is shot down, it is possible to launch a Crashed UFO ground mission to recover the craft.
- The UFO must be completely ignored, i.e. launching an interceptor and failing to shoot down the craft, either by it escaping or aborting the engagement will not generate UFO with Destroy Satellite mission.
- Ignored UFOs on Abduction or Terrorize missions will not generate retaliation UFOs, as well as ignored Overseers.
- If the difficulty level is Easy or Normal the retaliation UFO will only be generated if there are 3 or more satellites deployed.
A few days after the 1st UFO, a 2nd will be generated that will hunt the satellite over the country where the previous flyby took place. You will be told by Bradford that there's a new contact that gives off a distinct signature, "as if it is looking for something". The are only two types of UFOs used on this mission:
- Large Scout
- The Large Scout is replaced by the Battleship in June (Easy/Normal difficulties), May (Classic) or April (Impossible).
- The UFO will hunt for and destroy a satellite in the country it is patrolling.
- Completing the Stealth Satellites Foundry project reduces chance of the UFO to succeed from 100% to 25% on the first pass, and from 100% to 50% on its second pass (source: DefaultGameCore.cfg).
If the satellite is destroyed, panic in the country will rise to level 5 and it most likely will leave the Council at the end of month, unless the panic level is lowered. It is always a good idea to have a spare satellite to launch immediately if a satellite is destroyed unexpectedly.
- Final Preparation is the mission undertaken by the Overseer UFO.
- This UFO only appears after the Hyperwave Relay is built.
- If the UFO is shot down, it is possible to launch the Assault Overseer Storyline mission, the Crashed UFO ground mission to recover the craft alien.
The alien artifacts that can be gained from ground assaulting the UFOs are also highly variable, depending on UFO size with heavily damaged and crashed UFOs giving lower salvage versus a pristine Landed UFO (higher numbers). Destroying UFO walls by use of explosives or stray shots will further deduce from the amount of salvage, as well as fires started by weapon fire or Cyberdisc explosions will eat up walls and even destroy UFO Flight Computers or UFO Power Sources they come in contact with, also reducing the amount of salvage.
|UFO||Elerium1||Crashed Min||Crashed Max||Alien Alloys2||Crashed Min||Crashed Max||Alien Food||Alien Stasis Tank||UFO Nav Computer||Alien Surgery||UFO Power Source|
| 1 25 Elerium per Power Source. On Easy Difficulty mode, recovered Elerium increased by 20%. Elerium on Crashed UFOs can vary between 50% and 75% of total value|
2 On Easy Difficulty mode, recovered Alloys are increased by 25% and in a Crashed UFO they vary between 50% and 90%.
3 Plus 2 Fusion Cores.
4 Plus 1 Ethereal Device.
Values for the Enemy Within DLC.
The larger components of UFOs also have defined percentages for surviving a crash:
- UFO Power Source - 33%
- UFO Flight Computer - 50%
- Alien Surgery, Stasis Tank and Food - 25%
- Ethereal Device - 100%
- If a EMP Cannon is used to bring down the UFO, the salvage percentages above, including those of Elerium and Alloys, are all increased to 100%.
Each UFO will be manned by aliens, consisting of a commander type unit (Outsider, Sectoid Commander or Ethereal) and additional aliens. Their total numbers depend on the status of the UFO, landed craft will have more aliens present than a crashed one, and the size of the UFO. Larger UFOs (from Abductor above) will also have some of the larger alien species such as Berserkers or Sectopods. It is unknown the effect that EMP Cannon has on crew numbers.
For complete numbers and types of aliens during UFO missions, see Alien Deployment.