UFOs

In other languages: 한국어.

The UFOs seen in the skies of UFO: Enemy Unknown are big, blocky, geometric shapes that lack any form of aerodynamics. They are able to fly at breakneck speeds through the power of Elerium-115 and the resiliency of Alien Alloys. UFOs come in a variety of forms ranging from the tiny Small Scouts right up to the massive Battleships.

UFOs are the aliens' sole method to get to Earth, so in theory, it would be possible to halt the alien advance if X-COM could maintain absolute air superiority. Earth's forces do not initially have the resources required for such a task, and even if it becomes possible, the aliens have a vast resource supply and will not be set back by a war of attrition. In addition, alien undercover agents will continue to erode Earth's defenses from the inside.

Despite this, commanders should still shoot down as many UFOs as possible. At the very least, it may slow the aliens down temporarily. In the long run, it will actually further antagonise them, causing the aliens to accelerate their agendas. In any case, captured alien technology is essential to our research and finances.

Alien Subs are the equivalent in Terror from the Deep. The third game in the series, Apocalypse, introduced another fleet.

UFO Interiors

The core components of a UFO are UFO Navigation, UFO Power Source, Alien Alloys, and Elerium-115. You will recover less from crashed UFOs, but sometimes it's critical to shoot them down. Larger UFOs may contain additional equipment such as Alien Surgery, Alien Food, Examination Rooms, and even Alien Entertainment.

UFO hulls and interiors are composed of Alien Alloys. This provides incredibly light, yet strong, armour - perfect for spacecraft construction. The only field weapons able to punch the outer shell of a UFO are Blaster Launchers. The interior of UFOs are also very strong, but made of much thinner alloys that can be destroyed by repeated fire from Heavy Plasmas, the Tank/Laser Cannon, Hovertank/Plasma not to mention the Blaster.

Great care should be taken when clearing out a UFO. The interiors of larger UFOs are often deadly mazes, with tight corridors, and sharp corners, and choke points that even a single alien can defend. An inexperienced squad leader will also often face dead ends, or encounter treacherous storage rooms - most of the time these are empty, yet occasionally an alien will hide in them to ambush your soldiers. Two UFOs even have trapdoors - the Terror Ship and the Harvester, which the aliens frequently use.

Squad leaders should also use explosives wisely. A stray explosion may accidentally damage precious Elerium-115 or set off secondary reactions. The low ceilings also limit the range of Grenades. The tight spaces do, however, make Proximity Grenades particularly useful, and grenade explosions can go around corners to hit aliens lying in wait.

UFO Types

The UFOs deployed by the aliens range in size and the mission profiles they are most commonly seen on, some are also much more common to certain of the alien races encountered.

Very Small UFOs

Small Scout - Very Small UFO that looks like an Apollo capsule. Primarily used for research.

Small UFOs

Medium Scout - The classic 'flying-saucer' craft. Able to fill a variety of roles.

Large Scout - Cross-shaped UFO, slightly larger than the Medium Scout. Very versatile.

Medium UFOs

Abductor - Medium-sized UFO used primarily for human experimentation. Always crewed by Sectoids or Floaters.

Harvester - Medium-sized UFO with food and surgery units. Used to abduct cattle for food. Never crewed by Snakemen or Ethereals.

Large UFOs

Terror Ship - Large UFO used to unleash assault teams and Terror Units on residential areas.

Supply Ship - Large-sized UFO for transportation of aliens, food, and other supplies.

Very Large UFOs

Battleship - Very Large UFO used to intimidate Earth's peoples and leaders, and to assault X-COM bases, along with a variety of other roles.

Quick Comparison Table

Craft	Size	Max Speed	Escape Time*	Weapon Power	Weapon Range (km)**	Firing Interval***	Damage Capacity	Points (Crashed)	Points (Destroyed)
Small Scout	Very Small	2,200	200	0	0	N/A	50	50	100
Medium Scout	Small	2,400	250	20	15	56	200	75	150
Large Scout	Small	2,700	300	20	34	48	250	125	250
Abductor	Medium	4,300	500	40	22	48	500	250	****
Harvester	Medium	4,000	500	40	20	32	500	250	****
Terror ship	Large	4,800	2,000	120	42	24	1,200	500	****
Battleship	Very Large	5,000	4,000	140	65	24	3,000	700	****
Supply ship	Large	3,200	3,000	60	36	24	2,200	400	****

* Actual interval before UFO flees is calculated by randomly increasing this value by 0-100%, then subtracting 30 per difficulty level. For example, the Small Scout on Superhuman (difficulty 4 in the game code) will attempt to flee after 80-280 frames. The Acceleration value in the in-game UFOpaedia is not used.

** The figures given in the in-game UFOpaedia are a factor of 8 too high, relative to Craft Armament ranges.

*** Actual interval between UFO attacks is calculated by subtracting 2 per difficulty level from this value, then randomly increasing the result by 0-100%. For example, the Battleship on Superhuman (difficulty 4 in the game code) will fire every 16 to 32 frames (average 24).

**** Only the Small Scout, Medium Scout and Large Scout can be destroyed.

• All UFO weapons have an accuracy of 60%.

Weapons vs. UFOs

• As the Small Scout cannot return fire, it can be attacked safely with any weapon whatsoever. If X-Com wishes to perform a UFO Crash Recovery on a Small Scout, weaker weapons such as the Stingray, Cannon and Laser Cannon must be employed, as stronger weapons are guaranteed to destroy the UFO outright. However, this is generally more trouble than it's worth, as Small Scout recoveries only have one alien and one unit of Alien Alloys; moreover, the aforementioned weapons all have short ranges, and an Interceptor will rarely be able to close to such a range before the agile Small Scout flees.
• The Medium Scout's short range allows any weapon except the Cannon to be used with impunity. Use of Plasma Beams or Fusion Balls has a small chance to destroy the Medium Scout, which is generally undesired.
• Avalanches or Plasma Beams are generally preferred against the Large Scout due to its long weapon range of 34 km. However, as this UFO's weapon is quite weak, Stingrays and Laser Cannons are viable alternatives.
• The Abductor and Harvester have short-range weapons, enabling the use of Stingrays (and, in the Harvester's case, Laser Cannons). When using Avalanche missiles against these UFOs, care should be taken to avoid the "last shot out of range" bug, as all three salvos are often necessary.
• The best weapon for shooting down Terror Ships is the Plasma Beam, due to its long range and enormous ammunition reserves. Before X-Com obtains Plasma Beams, Avalanche missiles can be used safely; however, due to the Avalanche's low ammunition capacity, two Avalanche-armed craft must be used (again, as almost all the missiles need to hit, the "last shot always misses" bug should be carefully avoided). Attempting to use Stingrays, Cannons or Laser Cannons against a Terror Ship will usually see the offending Interceptor blown out of the sky.
• There are no weapons which outrange Battleships, so interception craft will always have to endure their powerful return fire. The safest strategy for shooting down a Battleship is to intercept it simultaneously with two Firestorms or Avengers each armed with dual Plasma Beams (a single Avenger will suffice, but may need weeks of repair). If advanced craft are not available, the Interceptor's best hope is to use dual Fusion Balls (they inflict damage more rapidly than Plasma Beams, and reduce the time exposed to return fire due to equalling a Battleship's range), but this requires at least three Interceptors due to the Fusion Ball's low ammunition capacity.
• X-Com should use the Plasma Beam to shoot down Supply Ships. None of the earlier weapons are effective; the Supply Ship's health greatly exceeds the ammunition capacity of the Avalanche, whilst other weapons put the Interceptor in danger from return fire.

Interceptors Vs. UFOs

• The Interceptor is slow compared to UFOs, so any alien craft it is chasing must slow down. The "sluggish" Small Scout can outrun it!
• The Firestorm can handily intercept all UFOs except the Abductor, Terror Ship, and Battleship, which must be going lower than top speed for the Firestorm to catch up.
• The Lightning can be outrun by the Harvester, Abductor, Terror Ship, Battleship, and Supply Ship.
• The Avenger can hunt down and attack any UFO in the game easily, due to its massive speed.

UFO Behavior

Aliens in their UFOs will behave in a different manner depending on what sort of mission they are tasked. All currently available data is summarized in the following points. UFOs will ALWAYS head to their mission locale (as listed in the Hyper-Wave Decoder information) at top speed and then initiate one of the following behaviors depending on the mission:

• Most UFOs will slow down continuously as they prepare to land. Check the altitude to try and guess when and where they're going to land so you can do a UFO Ground Assault.
• Certain missions are done by several ships instead of just one. These are Alien Base and Alien Infiltration missions.
• Alien Research mission UFOs will slow down significantly and do several slow sweeps as they probe for data, also landing for brief periods.
• Alien Harvest and Alien Abduction missions will sweep an area at moderate speed and land multiple times as they locate and abduct cattle and humans.
• Alien Infiltration ships will land in the cities, in the country they are attempting to infiltrate. Scouts of various sizes will appear and maybe land. Later, they will send Supply Ships, Battleships, and Terror Ships in an attempt to bribe and scare the country's leaders into submission. X-COM will lose funding from this country and an Alien Base will appear if the mission is successful.
• Alien Retaliation ships will scout a specific area where they have been having trouble, in a manner similar to an Alien Research mission. If your base is nearby, shoot the UFO down. Once an X-COM base is located, the aliens will send a Battleship directly at it at top speed, low in the atmosphere.
• Alien Base missions will behave in much the same manner as Alien Research. When constructing the Alien base, a fleet of Supply Ships and Battleships will land often as they search for a suitable location. One Battleship, two supply ships, and three Large Scouts is common.
• Supply Ships on an Alien Supply mission will be dispatched at exactly 00:30 and will land only once, directly on top of the base. Supply ships on this type of mission will run at full speed their entire time, not even slowing down as they land. They only stay on the ground a short time, so advanced craft are needed to deal with them if they are airbourne.
• Alien Terror UFOs will slowly meander about looking for a city for the Terror Ships to land at. If the scouts are shot down, the first Terror Ship will behave much like the scouting UFOs. It may iniitiate a terror mission, although rare. If the scouts are not shot down, the Terror Ship will arrive in the region, slow down to pick a city, and then land. The possible second Terror Ship (if you forced the Aliens to scout with a Terror Ship) will pick a city and then land, regardless.
• If you are successful at preventing lesser UFOs from doing their jobs, the aliens will eventually send Battleships to do the dirty work, hoping you won't be able to attack them. (They will not participate in Alien Research and Alien Terror missions, though.)