Base Defense (Apocalypse)

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How to defensively build and protect your base when under attack by hostile ground forces.
Important: Immediately defend a newly purchased X-Com base by flying heavily armed X-Com agent(s) to the building. They will be visiting the building until the Living Quarters is built and must carry all their equipment and bulk ammo until more can be transfered once the General Stores is also built.

Hostile Intent

An X-com base targeted for destruction by any ground force will immediately start a battlescape Base Defense mission. Agents and any technical personel will come under attack. If all your units are neutralised (panicked, stunned, mind-controlled, killed, or escaped), the mission is a failure and the base is destroyed, including the available 'base slot'.


Disregarding the Cityscape aspect of location and building type, the layout of the corridors surrounding the Access Lift determines the ease of defending the base, and its most suitable operational objective. Large open areas surrounding a centrally positioned access lift will be more difficult to defend (limited effectiveness and cover of security stations) than a layout with an access lift located in an isolated area or single corridor.

Security Stations

Using Security Stations is vital to limit the invaders chance to 'explore' your base for vunerable personel and damage to facilities. A single base is limited to using three security stations at any one time. More than three, the active stations are randomly chosen at mission start. As a battlescape mission progresses, a station may be so significantly damaged that the lower section becomes a crater from multiple large explosions, blocking all movement for all ground-based entities.

Access Isolation

Hostile forces will gain entry to the base via facilities which open out to the cityscape: the Access Lift and Vehicle Repair Bays. Security stations placed adjacent, in a choke-point fashion or cross-fire orientation, will inflict heavy damage on any invadng force.

Personel Limits

A base defense battlescape has a total X-Com unit limit of thirty, of the maximum of thirty-six slots.
If a base has a large population, the pool of agents and technical personel are chosen randomly: agents are assigned a third to half of the unit slots with the rest being filled until the total limit. An agent will always be available from the population.

Stand-Off Tactics

Wait for hostiles to make it past security stations. Don't attract their attention until the turrets are no longer firing or have been destroyed.
Hostiles moving throughout the base take the most direct path to wherever they are going. Placing armed proximity mines in these areas pre-emptively should clean up any stragglers who made it past the security stations. Mines placed in doorways will detonate when flying units come down to get through. To avoid proximity mines with your own agents: micro-manage their movement to 'take the other door' or 'move up the far side of the corridor', etc. If Boomeroids are used, that thoroughfare is now off limits to X-Com - plan your movement carefully around such devices since they will move about (overhead view, purple dot).
Destroying ramps and stairs inside the repair bays completely stops ground units one-way, but your ground troops must now jump off the ledge to preceed the other way.
If the layout allows or your base is sparse, three unused corridors in a line is a death zone for hostiles since manual fire (select agent, hold shift) past the unseen units towards a far wall (depending on the weapon over-shoot) will hit anything in the way.
When hostiles are approaching from a side corridor, throw boomeroids forward (set bomb, don't RMB-throw) into the corner to get the bomb to jump immediately towards approaching entities ...otherwise don't since your retreat and regroup will be painful. Don't Get Hurt!
Enhance the power of a proximity mine by thowing an unarmed high explosive next to it. A Power Sword can make narrow shortcuts through the concrete wall. Cut away high up to stop ground forces using the new corridor. The only threat will be Skeletoids since they can fly. A Psimorph won't fit.
Defensive craters in a corridor to remove flanking opportunities for enemy units is a very desperate tactic.
Hostiles grouped around their dead friends is an easy target for a thrown grenade to set off the dropped ordinance. An impromtu cook-out cook-off!
Scientists and Engineers are helpless when faced with a hostile unit. Avoid exposing them to any deadly threat whatsoever (eg: weapon overshoot) by moving them into the farthest sections of the base away from the lift or repair bays. If the battle is not going well but there may be chance to succeed, destroying the route towards their hiding place (explosives or cutting) to isolate them from hostiles can prevent any deaths. If the base layout allows and there are multiple paths to the access lift, flank the main group fighting, to reach the access lift a dangerous and desperate tactic but it works if you have another base available: Use one unit to scout the route. If detected, one unit is killed. If it is safe, run all your technical personel out the access lift and escape!
Trying to save those dropped exotic items for new reaserch or to sell off is not the priority... it is Base Defense!.

Theft Of Funds

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.

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See Also