Battlescape tactical missions commonly follow certain Alien actions within Mega-Primus. Certain mission types may be started by X-Com, as well.

Already Infested

At the start of X-Com Apocalypse, there already is an alien infested building! It is unknown where, and there is no way of knowing until a security force finds evidence within their buildings. An "Alert Detected" is displayed for X-Com's immediate attention with the building in question circled in red on the overhead cityscape view. The alien menace must be dealt with immediately!
Note: since there is no way of knowing where (unless you save/load), searching random buildings is not worth the effort nor the decreased reputation of such action, however, searching your own building has no negative effect... and you might detect aliens!

Searching A Building

A search for alien infestation inside buildings will be necessary to eradicate aliens and to cease their infiltration and subversive actions. If aliens are detected, a battlescape mission immediately starts with the objective to kill the alien menace (without damaging the structure). If no alien lifeforms are found, the organisation inconvenienced by such a distrubance will file a protest by becoming very slightly more hostile.

First Assault

The first mission can be troublesome (Brainsuckers!) or it can be extremely easy.

Troublesome

Equip all your agents with any available projectile weapons and spare clips (armour is optional). Place them onto the Valkyrie and go to Alien Alert when it appears. Once it starts, direct your fire onto the Brainsuckers as they approach. If a pod lands at/near your agent's feet, quickly access their inventory and pick up the pod. Doing so will stop the pod from bursting open. Hang onto the pods or hatch them in a controlled manner. You do not have any means of capturing live aliens at this stage, so kill all of the aliens.

Extremely Easy

Hire one Android, if available. Equip this robot with a weapon. Grenades and armour are optional. Send this one agent to the alien alert. After the mission starts, run around the map and find the brainsuckers. Since your android does not have a brain, brainsuckers pose no threat whatsoever, and since the Anthropods are carrying brainsucker launchers, they cannot harm your agent. Shoot all aliens at point blank range to conserve ammo.

Warnings About First Mission

If your score total is higher than 1000 before you start this mission (from raiding), some aliens might carry disruptor guns.
a score above 2500 before you start: aliens can use boomeroids.
score above 8000: devastators, vortex, shields.
above 25000: devastators, entropy, dimension, teleporters, cloak, shields, vortex.

Investigation

This mission type is triggered when you have Agents in a Mega-Primus building and select the "Investigate building" option on the building screen. A mission will only occur if there are in fact aliens in the building; otherwise, you will receive a message informing you of the lack of aliens and a relations penalty with the organisation owning the building due to the unnecessary inconvenience. You will also receive this message if the only aliens in the building are Multiworm Eggs and/or Chrysalides; fortunately, this is rare.

This mission type will take place in a map randomly generated from modules according to the building type. The number of modules used varies with the number of units in play.

Opposition consists of all aliens currently in the building (unit limits permitting). If the owner of the building is hostile to X-COM, you will also face their guards. If the owner is also hostile to the Aliens, a three-way battle will ensue - this may result in the aliens being slaughtered by the guards before X-COM ever locates them.

To win the mission, kill or subdue all opponents. Note that damage to the building will cause a relations penalty. Aliens that escape the combat area during the battle will move to a neighbouring building, as will all remaining aliens if X-COM retreats from the battle.

Raid

This mission type is triggered when you have Agents in a Mega-Primus building and select the "Raid building" option on the building screen. You cannot raid buildings owned by X-COM.
Like an investigation, this mission type will take place in a randomly-generated building map. Unlike an investigation, random items will be placed at certain locations on the map.
Funds may be stolen due to the presence of invaders. Base facilities damaged are automatically repaired at the end which may further impact funds into a negative amount. X-Com may initiate a raid of any building, hostile or not, at any time. The funds of the X-Com targeted organisation (either you are attacking or being attacked) does not matter. The equipment of the enemy is based on the week. The quantity of enemy present will be always the same. It will be reduced if X-Com uses many agents to attack, or they are many scientists and engineers along with agents and turrets present at a base defense mission.

Opposition consists of the building owner's guards only. Any aliens in the building will not be present.

To win the mission, kill or subdue all the guards.

Note that the only real purpose of raiding is to acquire money and/or items (via stealing random "loot" items and/or the guards' own equipment). While it will cause the building owner's balance to drop, this doesn't have any significant effects.

Raiding A Building

Raiding is used to cause damage to the internal structure of the building, to injure/kill the security forces present and to steal anything you can find. Raiding immediately starts a tactical mission and is a good way train troops - as long as they don't die.

Raiding a corporation and causing damage to the building or its guards will cause it to become more hostile towards X-COM. The corporation's allies will also be angered by X-COM's actions.

Openly attacking enemy guards will cause them to instantly become hostile if any of their hit points are lost. Hit points lost through their own fault or through indirect damage such as fall damage will not be counted. Indirect damage to any guard while under X-COM mind control will initiate the hostilities.

If the aliens are present inside the building when it is raided, there is a very likely chance that they will appear during the raid, forcing you to contend with a mixture of aliens and guards. Guards are also likely to appear when searching premises owned by hostile organizations.

Advanced Search And Raid

If an organisation is under alien control, searching for aliens does not always start a tactical mission. And, raiding a building will sometimes involve fighting aliens and security forces.
If you are raiding a building and you do not destroy or kill anyone, then the corporation does not become hostile. To end this tactical mission, you must either stun everyone or retreat from the map via the blue exit squares or press ESC. Keep in mind that any form of damage to the building will be noticed, even if you are not responsible.
Multiple raids do not affect a corporation's ability to equip its security forces with weapons. It only angers them more and if you are successful, it gives you something to sell and gives you an increased score at the end of the month.
Only works with air vehicles: Immediately after the completion of a tactical mission, you can click the building again and find that your agents and vehicles are still present at the building. You can do multiple raids before the vehicle actually clears the launch tube.

Vehicular Attacks

Using vehicles to attack a building before going in for a raid or search does not affect the floor plan of the tactical mission, nor does it affect the potency of its security forces. All it does it anger the corporation and cause it to launch defenders. It also decrease you score at the end of the month due to city damage.

Note: it is possible to flatten a building that you can no longer perform searches or raids. Launch tubes can also be destroyed to prevent ships from landing or taking off. Do not rely on this all the time as some extreme cases allow enemy ships to launch directly off the ground.

Base Attack

If you need to defend a newly purchased X-Com base and are waiting for the Living Quarters to finish, move an agent to that building. If the building is targeted for a Raid (or Alien drop), the agent(s) present will defend the struture as if it were an X-com Base Defense mission.

The only type of mission X-COM does not initiate, a Base Attack will occur if either a UFO drops aliens directly into an X-COM Base (aliens spreading to a base through the People Tubes must be found through investigation) or if a hostile organization randomly decides to "raid" or "storm" one. Megapol, the three gangs, and any infiltrated organisation are three times as likely to perform a Base Attack compared with other organisations. If there are no X-COM units present at the base whatsoever (even technical personnel), the raid will automatically succeed and destroy the base; otherwise, this will result in a Tactical Combat Mission.

In these missions, you control not only Agents, but also any technical personnel at the base. If there are more than 36 X-COM units at the base, who you get is random - it is unfortunately possible to receive no Agents at all even if there are a couple present. X-COM's units will, however, be assisted by any Security Stations at the base, although the turrets are unfortunately not manually controllable.

Base Attacks will occur inside an X-COM Base itself, with terrain varying depending on what modules you have in the base. Intruders will spawn inside the Access Lift and/or any Vehicle Repair Bays; X-COM units can spawn in any completed module except Vehicle Repair Bays (the Access Lift is not excluded).

To win the mission, kill or subdue all intruders. You will lose the mission, and the base with it, if all your personnel flee the battle or are killed - Security Stations don't count. If you lose your last base this way, you will get a Game Over.

UFO Crash Site

If alien craft are shot down in Mega-Primus (by X-COM or, rarely, others), they will usually crash-land. Sending a manned air vehicle to the crash site (with "Go to map point") will initiate an attempt to recover the wreckage. If the craft is a Probe or Scout Ship, this will occur instantly and automatically (as there are no crew). Attempting to recover any larger craft, however, will result in a Tactical Combat Mission.

Note that only air vehicles can perform crash site recoveries, as road vehicles cannot leave the road to reach the crash site. Additionally, only one vehicle can perform the recovery - this is a powerful incentive to keep a Valkyrie Interceptor or Hawk Air Warrior available until hybrid aircraft are developed.

These missions will occur on a special map, with the crashed UFO in the middle and all aliens initially on board. The map is always the same for a given type of UFO, and is not randomised. Opposition consists of the UFO's crew.

To win the mission and recover the UFO, kill or subdue all the aliens. Note that you have only one chance to succeed per UFO; if you retreat from battle, the aliens will blow up their craft (and themselves with it) to avoid capture. This will also happen if you ignore a crash site for more than a few in-game minutes.

Alien Dimension

The Alien Dimension is a dangerous place. Don't Get ~~Hurt~~ Shot Down.

Do not move agents from a landed craft to the building.

A large force is preferable (+24 agents) armed with the best. Aliens killed will drop useful items also.

To start the building assault once landed at a building, select "Investigate Building" or "Raid Building". Both buttons do the same thing.

A typical alien building battlescape occurs on a large map (3x3 battlescape segments), with a single 2x2 segment being the spawn spots for alien forces, and two 1x1 segments for X-Com. The other three 1x1 segments fill out the battlescape.

The "orange pad" terrain feature found in most buildings is an alien device for re-inforcements to spawn in at regular intervals, with the alien type relevant to that particular building's purpose. The orange alien spawn device is robust and can only be destroyed by Vortex Mines (or accidently by the Queenspawn). To halt such re-inforcements, all orange pads present at one device must be destroyed to disable it.

To complete your objective, all of the targets outlined in the Briefing must be destroyed. The message bar will display "Building has been disabled". To finish, evacuate the condemned building via the exit tiles or kill off all remaining aliens.

To unlock the Alien World Incursion missions, one must first visit the Alien Dimension with any hybrid craft. After that, the Quantum Physics topic The Alien Dimension will appear, which in turn unlocks the first of a series of Biochemistry topics named "Alien building". Completing this topic allows the first Alien World Incursion mission to be performed, which will unlock the next "Alien building" topic, and so on. As such, these ten missions must be done in order.

Note that, when one of these missions is completed, the associated structure will collapse on the Alien Dimension Cityscape. Do not launch your craft until the animation is complete, or it will be "destroyed by collapsing building".

As the final alien structure and thus the final mission of the game, there are a few differences between the Dimension Gate Generator and the other nine Alien World Incursion missions. See its page for details.

Tactical Combat Missions (Apocalypse)

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