XCOM (eXtraterrestrial COMbat) is a clandestine military organization formed by the world's nations to combat the alien threat. The player is the supreme commander of XCOM who controls all of its operations. The player can engage in many tasks as the commander, from research and base management, to controlling soldiers on the ground.
XCOM is formed when The Council initiates the XCOM Project in response to the alien invasion. It's composed of the best of the best military and scientific personnel the nations have to offer. XCOM serves as first and last line of defense of Earth.
The XCOM Project is a top-secret project initiated by The Council to counter the massive global alien invasion after the world's conventional militaries couldn't stop them. This project composes some of the best and brightest military and scientific personnel dedicated to defend Earth and their new technologies are developed from recently captured and reverse-engineered alien tech.
Leaders
The Council consists of a group of 16 countries that support the XCOM Project. The monthly rewards gained from The Council depends on the satellite coverage over individual members. Additionally, if more members from the same continent gains satellite coverage, the player will receive additional scientists and engineers in its monthly rewards. If all members of a continent are covered by satellites you gain the same bonus reward as the ones granted by your base starting location. Each council member have a panic level which increases if an alien activity occurs in the country that the player did not choose to investigate. Once the panic level reaches a critical level, council members will pull out from the XCOM Project permanently, which will affect the monthly funding. If eight members pull out of the Project, the game effectively ends in a defeat. Launching a satellite will lower the panic level of a member country by two. Once a continent has full satellite coverage, no abduction missions will spawn for that continent anymore. The amount of funds received is also adjusted according to difficulty level as shown in the table on the right.
Soldiers
A Soldier is a unit you use for combat in XCOM: Enemy Unknown. Each time you get a soldier they are randomly given an appearance and a nationality. They are housed in the Barracks. Soldiers are the most important unit in game, since they are the ones who perform Combat. Without any, you can't defend Earth from the Aliens. Initially, your squad will only allow four soldiers, but you can purchase upgrades from the Officer Training School to increase the size, to a max of six.
The Heavy Class is one of the Soldier Classes in the game XCOM: Enemy Unknown. The primary role of the Heavy Class is delivering large-scale damage to as many targets as possible, through the use of explosive ordnance or heavy gunfire. It is the only class capable of using Rocket Launchers, which provide high area damage and demolish obstacles. Rookie promotion is slightly weighted toward classes you have less of, but promotion is otherwise completely random. The heavy is a frontline fighter that excels in winning straight fights with sustained fire from high cover. It also has explosives to break up enemy positions and to level the playing field if overwhelmed. It also excels at destroying enemy cover as not only the explosives damage cover, but heavy weapons innately damage cover more than other weapons. Like the other classes, there are two promotion paths for the Heavy. The left side turns the Heavy into a demolitions expert, whereas the right side focuses on holding the line and utility. The Heavy Class leans towards stationary positioning, as many of the class' abilities only work when no movement is made. The Bullet Swarm ability allows the Heavy to shoot (or shoot then move, reload, or keep overwatch) twice per turn, making it extremely devastating in stationary shootouts. To make the most out of the class, it is advisable to position the Heavy behind the best available and the most durable cover, to minimize the need for movement. Conversely, the Heavy is also very effective at dealing with enemies in cover, either through rocket weaponry or the Suppression ability. Rockets can hit many enemies at once and destroy their cover, exposing them for gunfire from your other troops. Suppression can be used for dealing with enemies hiding behind indestructible cover, minimizing the risk for your soldiers by reducing the enemy aim.
The Assault Class is one of the Soldier Classes in the game XCOM: Enemy Unknown. The primary role of the Assault Class is aggressive reconnaissance, flanking, and drawing enemy fire. As the first and last unit on the ground, these troops are initially equipped with XCOM's proprietary combat shotgun Rookie promotion is slightly weighted toward classes you have less of, but promotion is otherwise completely random. Assault Class soldiers can be equipped with rifles, sidearms, and it is the only class that can equip shotguns. Defensive abilities (left side) allow the Assault to effectively "dodge" enemy fire by increasing Defense, safely move under reaction fire and can protect from critical hits. Offensive abilities (right side) improve critical chance, critical damage, and offer free reaction shots in close quarters combat. Developing on defensive leans towards scout and tank duty, while developing on offensive leans towards assassin duty or frontal assaults. Regardless of the chosen development path, it can be advisable to always pick Rapid Fire and Lightning Reflexes abilities due to the unique advantages they provide. Rapid Fire effectively doubles the soldier's gunfire output at close and middle range, and when flanking the enemy, while Lightning Reflexes allows to safely "soak" the gunfire from aliens on Overwatch, making the Assaults ideal point men for advancing the squad however; flush works quite well when paired with an assault rifle type weapon as it can be used over a much greater distance than with a shotgun and can be used on suppressed enemies to grant an immediate reaction shot to whomever is suppressing the enemy, conversely this also can be used on an enemy who is suppressing one of your units to force them to stop shooting and move to another location, also; it can be used as an inefficient but effective way to eliminate low health or otherwise weakened enemies that might otherwise not be hit by the soldier and can also be useful for weakening enemies that you are trying to capture that might otherwise be killed by a normal attack. Close and personal is superb for shotgun wielding soldiers fighting in tight quarters and is particularly effective versus melee opponents; this only increases in effectiveness with a soldier with all the offensive type abilities.
The Support Class is one of the Soldier Classes in the game XCOM: Enemy Unknown. Soldiers trained in the support class serve as both field medics and logistical support to the squad they are attached to. Equipped with medical supplies, smoke grenades and other items, these troops ensure the safe return of all units deployed in the field. The primary role of the support class is to keep the team alive and / or provide covering fire. They can learn to use medikits more efficiently, to cover the battlefield with smoke grenades and the ability to run further than other classes. Their covering fire and suppression abilities can help control enemy movement on the battlefield. Rookie promotion is slightly weighted toward classes you have less of, but promotion is otherwise completely random.
The Sniper Class is one of the Soldier Classes in the game XCOM: Enemy Unknown. Specialized in dealing large amounts of damage from extreme range, the sniper is invaluable resource for both scouting and surgical elimination of enemy units at long distances. Please note: Sniper are not suited for close-quarter combat without supplemental training. Rookie promotion is slightly weighted toward classes you have less of, but promotion is otherwise completely random. The primary role of the Sniper Class is to quickly kill priority targets or dispose of a few weak targets. The unique characteristic of the class is the focus on long range combat: unlike other weapons, sniper rifles have greater accuracy at long distance, and suffer reduced accuracy at close and mid range. Available abilities allow snipers to develop into two general types — Mobile and Stationary. Mobile is generally better for missions where lots of movement and CQC is expected (like alien ships and hostage rescue.) Stationary is better for open missions (like abductions and alien bases.) Most disadvantages can be mitigated by creative planning and proper implementation of strategy.
The Psionic Class is a special sub-class in the game XCOM: Enemy Unknown. Any of the other four classes can access this class as an add-on to their own abilities, however the psi-abilities only unlock for soldiers who possess "the gift", which can be determined by testing in the Psionic Lab. The primary role of the Psionic Class is mental domination of the battlefield, turning enemy troops against themselves and their allies which is very useful. "Defensive" abilities allow Psionics to defend against mental attacks from Sectoids and Ethereals and providing defensive boosts against incoming fire. Psionic Class soldiers don't have any special restrictions on weapons which can be carried, other than those their main class allows. Psionics have access to special Psi Armor which provides a +30 boost to their psi attacks and defence. (Although the stats on the character screen indicate that this boost is only +20.)
Support
Engineers are employees of XCOM in XCOM headquarters's Workshops in XCOM: Enemy Unknown. Headed by Dr. Shen, engineers both manufacture and upgrade the various weapons, armors, equipment, and aircraft used by your soldiers. However, they cannot upgrade equipment until you have built a Foundry. You can tell how many engineers you have by visiting Engineering and looking at the bottom-middle of you screen.
Scientists are employees of XCOM in XCOM headquarters's Laboratories in XCOM: Enemy Unknown. Headed by Dr. Vahlen, scientists perform valuable research that allows your Engineers to build different weapons, armors, equipment, aircraft and facilities. You can tell how many scientists you have by visiting Research and looking at the bottom-middle of you screen.
SHIVs
The S.H.I.V. is a weapons platform in XCOM: Enemy Unknown you can manufacture in the Engineering Lab. The Super Heavy Infantry Vehicle, or S.H.I.V., is an advanced weapons platform that can be deployed in place of a human soldier. While extremely capable in most combat scenarios, any damage to the S.H.I.V. will require lengthy repairs.
The Alloy S.H.I.V. is an upgrade to the S.H.I.V. in XCOM: Enemy Unknown. Integration of the alien alloy into the basic S.H.I.V. design results in a weapons platform that is both lighter and stronger than the original. The reinforced chassis allows for this S.H.I.V. to be used as a mobile cover position in the field.
The Hover S.H.I.V. is the final upgrade of the S.H.I.V. in XCOM: Enemy Unknown. It's an upgrade from the Alloy S.H.I.V.. Our latest modification to the S.H.I.V. vehicle involves the integration of a small pulse engine, allowing the entire platform to fly over rough terrain.
Vehicles
Interceptors are hunter/killers deployed by XCOM to intercept and shoot down UFOs when detected by Satellites. Raven is an old type of Interceptor which can pack a punch on the UFOs. Firestorm is a new type of Interceptor which can better intercept and take down UFOs better than the Raven.
The Raven is an early type of Interceptor and predecessor of the Firestorm. Heavily modified and augmented fast attack fighter. Avionics, tracking and engines have all received substantial boosts. Armor and frame durability will be a major issue when engaging any but the smallest UFOs. Despite all this, the Earth's atmosphere is the Interceptor's best defense.
The Firestorm is an advanced type of Interceptor. Unlike normal interceptors which are ordered from the Hangar, it is produced at Engineering. The Firestorm is produced out of a reversed-engineered UFO's Flight, targeting computers, power source and Alloys. It is Dr. Shen 's "Proudest Creation". The Firestorm is our highly advanced combat aircraft incorporating numerous advances gained from studying the technology found in the alien ships. Power and navigational systems in particular were adapted directly from the alien designs.
The Skyranger is a Vertical Take-Off and Landing troop transport (VTOL) in service with XCOM in the game XCOM: Enemy Unknown. This vehicle transports the player's squad anywhere around the globe from base to any location and vice versa. It is piloted by the pilot codenamed Big Sky.