Base Defense (Apocalypse)

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How to defensively build and protect your base when under attack by an invading ground force.

Important: Immediately defend a newly purchased or recently undefended X-Com base by moving a heavily armed X-Com agent(s) to the building. They will be visiting the building if no living quarters are built and must carry all their equipment and bulk ammo. There are slight differences which depend on the reason why the base is undefended. (See below: Base Loss And Complications)

Hostile Intent

An X-Com base targeted for attack by any hostile 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, but not including the available 'base slot'. A new base purchase, if available, will again use this slot.

Invaders

The main entry into a base will be through the access lift. If vehicle repair bays are present, invaders often appear within.

Aliens will be dropped by a UFO hovering above the home-cell, or nearby but within the property outline (overhead view), in the same fashion as any other infiltration attempt. The infestation squad will be similar to the aliens typically aboard the type of UFO. The larger the craft, the larger the infiltration force.
Hostile organisations will attempt to destroy an X-Com base by kiling all units within, without any warning! There is no way to stop such action. A defensive layout of security stations and facilities will reduce X-Com losses, if any. Any damage will incur a repair cost after succesful defence.
Any organisation attempting an base attack will use their own defence forces:

Megapol will use Police.

Cult Of Sirius will use Cultists.

Gangs will use Gangsters.

Mega-Primus organisations will use Corporate Hoods instead of their own Building Security.

Hoods are hoodlums, thugs, junkies, criminals, hustlers, homeless bums, hookers, drug dealers, pimps, gang-bangers, street trash, hooligans, vandals, goons, villians, punks, someone named EsTeR, crooks, mobsters, bandits, etc.

Targets

What do they want? Money? Land? Equipment?...No.  DEATH TO X-COM!

Hostiles will move to random facilities searching for something to kill. Hostiles will not damage anything purposely. They do not destory the internals or anything else. They just want to kill.

Layout

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

Invaders 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 to the lift in a choke-point fashion or cross-fire orientation may inflict heavy damage quickly on invaders, destroying their morale.
Using Security Stations is vital to limit the invaders chance to explore your base for vunerable personel and prevent damage to facilities from combat. 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 ground movement for all units.

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. An agent will ~~always~~ be available from the population. Some errors may appear.

Building Garrison And Transfers

Troops moved to newly purchased base (see above: Important) will still be visiting after the living quarters is built. To allow these defenders to become members of the base, they must be transfered to it by using Transfer Screen or by manual delivery (ie: using your own craft to transport the agents, then move them off it and into the home-cell).

If a living quarters has available space, any manually delivered agents will automatically allow them to become members of this base however, if an agent has walked to this base (used the people tubes), this agent will be visiting irrelevant if living space is available. They must either be specifically transferred to this base or use a vehicle for manual delivery (as mentioned above).
Agents who are visiting do not use training, medical, psi-gym, etc. They don't belong to the base.
Using your own craft (ie: manual delivery) instead of using Transtellar's Autotaxi service, will lessen any risk to your agents and is faster.
Technical personel cannot be manually moved with a vehicle. They can only be relocated by using the Transfer button, and only by walking or by using a taxi.

Massive Damage & Repairs

Any damage, no matter how minor, will be repaired and paid for by X-Com, irrelevant of avaialble funds.
Any base facilites damaged completely (only floor tiles remain after all five levels have been completely demolished) will incur severe monetary loss. Any facility cannot be destroyed and will be still available as normal when returning to the cityscape after a succesful base defence, but X-Com's funds will be reduced due to repairs.

Stand-Off Tactics

Security Stations are ideally placed besides the access lift and vehicle repairs bays, if used:

Security stations are your first line of defence. Leave them to deal with any hostiles.

Do not garrison the security station with your own troops on the upper platform section. The whole room may suffer extensive damage.
If agents or technical personel appear next to the access lift or security stations at the start of the base defence mission, they are extremely vunerable and are often killed. The priority is to immediately escape by using the blue-exit-tiles, but only if others are available to defend the base. If possible, place on the ground via inventory a 0.25sec timed smoke grenade (do not drop or throw since it takes longer to detonate) and run towards the exit tiles or away from the hostiles! A stun grenade(s) or incendiary thrown away from your escape route and towards the hostiles may cause them to run away from the cloud of gas or fire, instead of firing at your units. The outcome of this dangerous situation depends on position, layout, hostile forces, agent equipment and luck.
Using a Motion Scanner is highly advisable.
Wait for hostiles to make it past security stations. Do not attract their attention until the turrets are no longer firing or have been disabled.
If the security facility has sustained damage to the walkways and stairs, hostiles may be prevented from moving past.
Enhance the power of a live proximity mine by throwing an unarmed high explosive next to it, but within its detection range.
Hostiles moving throughout the base take the most direct path to wherever they are going. Placing armed proximity mines in these areas pre-emptively could eliminate any stragglers who made it past the security stations. Mines placed in doorways will detonate if flying units move by on the same level as the mine. 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).
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!
A Power Sword can make one-wide shortcut through the concrete walls if an agent is flying. Cut away high up to stop enemy ground forces using the new corridor. The only threat will be Skeletoids since they can fly.
If the layout allows or your base is sparse, multiple unused corridors in a line is a death zone for hostiles since manual fire (select agent, hold shift) past the unseen hostiles towards a far wall (depending on the weapon over-shoot) will hit anything in the way. A weapon projectile will stop in mid air when an unseen hostile is hit.
Destroying ramps and stairs inside the repair bays completely stops ground units one-way, but your own ground-based troops must now jump off the ledge to proceed the other way. It is possible that movement may be halted for both sides. Alternative methods of killing the invaders should be used: X-Com agents waiting in ambush, blind fire of rockets towards hostiles last known location, liberal use of grenades into craters, tunneling with a power sword to bypassed broken stairs, or just wait for hostiles to escape. Use the motion scanner when moving slowly to detect hidden hostiles or (always) have a flying agent available.
Defensive craters in a corridor to remove flanking opportunities for enemy units is a very desperate tactic. Cutting/blowing away stairs and platforms is also a viable tactic.
Hostiles grouped around their dead friends make an easy target for a thrown grenade to set off the dropped ordinance.
Technical personel 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 access lift or repair bays. Destroying the route towards their hiding place (explosives or cutting) to isolate them will prevent the advance of hostiles.
If the base layout allows and there are multiple paths to the access lift, avoid the main fight to reach the access lift to attempt an escape ...is a dangerous and desperate tactic to save some technical personel if they are being pursued by hostiles.
Any units which escaped from the base will automatically return upon successful defence of the base.
Trying to save those dropped exotic items for new research or to sell, is not the priority... it is Base Defense!.

Base Loss And Complications

If your only base encounters a defence mission and is not successful for any reason, the base will be destroyed and you lose the game!
...however, if two or more other bases remain:

Any units which escaped from the base (they were moved onto the blue-exit-tiles within the battlescape mission) will move to the home-cell and will be visiting this building (your destroyed base) which is now a Government building.
Other bases ~~with living quarters~~ will accept all the displaced X-Com units. If living quarters are built somewhere and the base accepted displaced X-Com units, it will disregard the personel capacity:

Technical Personel from the lost base will become members of your (two or more - if not, see below One Base Remains) other bases but are stuck at the old home-cell. Their portrait picture denotes that they are visiting a building. They cannot be moved except via transfer. The only way to force these units to move out from the old home-cell and return to base, is to transfer them from their newly allocated base to any other base with Living Quarters and free capacity. They are in the list of base members somewhere but cannot be placed in a lab/shop since they are not present at the base. If multiple bases have taken these refugees, then each technical personel must be transferred somewhere else to make them move.
If you buy a base to enable the transfer button (transfer button is inactive if you have only one base - you had two but just lost one), you must wait for Living Quarters to be built. Salary will still be paid for the new week but your technical personel are idle.
Agents who escaped from the base defence mission before it failed, can be moved by Return To Base, picked up manually with an X-Com vehicle, or use "Go To Building".

One Base Remains

If it is not possible to purchase another base and you have technical personel which escaped from a failed base defence, the only option is to sack all units that escaped (except agents) from the lost base.

If they are gettin' the boot later, why not let them just be bullet sponges instead of escape!

Home-Cell Strangeness

If an X-Com base has just been bombed by hostiles and the home-cell was destroyed, but you did not get the message: "X-Com Base Destroyed", only the residing or visiting X-Com units are killed. Any road based vehicles may be damaged or destroyed. The layout, base facilities and air vehicles are not affected. You end up with an unattended and active, but home-cell-less, base!

If no units are present (...see Important top of page) and an X-Com-Base Attack mission is soon, the UFO ignores the state of the home-cell and will continue its mission. As there are no units where the home-cell once was, the base defence mission automatically fails and the base will be destroyed.
If X-Com agents are delieverd (using people tubes or flying vehicles - no road vehicles since home-cell is gone) to the base with the destroyed home-cell before any further X-Com-Base Attacks (note: not Building Bombing), then any new agents will have their icon at the same place as the destroyed home-cell. Any new weapon impact on this cityscape tile (accidently or purposely) immediately kills all present. Any weapon will do. Weak weapons which cannot normally destroy a buidling tile will kill everyone just the same!
The agents that have arrived after loss of the home-cell, they will defend the X-Com base as per usual.
If the home-cell is destroyed - or the base is lost - transfered or newly hired units which were already en-route (on foot or AutoTaxi) will still attempt to reach the (missing) home-cell. Walking units will reach the tile where the home-cell was previously if people tubes are intact but vehicles will only end up driving in loops since there is no road access. If Ultra-Fast time is used briefly, all units will reach the tile. The portrait picture within the Agent Tab will show all units at this destroyed X-Com base are visiting.
If at any time the message: "X-Com Base Destroyed" and UFOs are heading to the building with the intent of a X-Com-Base Attack, the drop blue rain animation will replace the grey-smokey-tube animation.

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