This mission occurs 10-20 days following the Alien Base Assault mission. While in Mission Control the Hologlobe will begin to behave erratically, followed by a cutscene where multiple XCOM personnel, under the influence of alien Mind Control, commit acts of sabotage and violence. The mission is launched immediately following the cutscene, without an opportunity for the player to choose and equip the squad members.
|“||Hostile forces have infiltrated XCOM headquarters and are moving in with reinforcements. We have to protect the base at all costs - if we don't hold the line here, any hope we had of stopping this invasion will be lost.||”|
– Central Officer Bradford, XCOM: Enemy Within
|“||The invaders have infiltrated XCOM HQ in unknown numbers. Limited reinforcements, including XCOM Base Security personnel, are available. Failure will mean the end of XCOM.||”|
– Mission Brief, XCOM: Enemy Within
|“||▪ Defend our base by all necessary means
▪ If all soldiers in the combat area are killed, XCOM HQ will fall
|– Mission Objectives, XCOM: Enemy Within|
This mission takes place on a unique map detailing the expansive XCOM HQ Delta Section, an area of the XCOM headquarters located behind Mission Control. The areas of Delta Section are identified as alien reinforcements arrive throughout the mission. Together they form an elongated rectangular shape consisting of a Rear Guard Station, Command Center, Mech Bay, Forward Access Tunnel, and Forward Guard Station.
The number (as many as 44 on Normal and Classic) and type of enemies vary depending on the stage of the alien invasion, similar to the Alien Base Assault. The exact composition of the alien force that the player faces is mostly randomized (as well as some of the alien spawn points). The alien force is randomized again when a player restarts the mission after failure, meaning that each attempt at base defense plays out differently.
The mix of aliens during base defense is not normalized, meaning that a player may face an "easier" mix with more Sectoid thrown in, or a harder mix with stronger aliens. It is possible for this mission to feature every alien type with the exclusion of Outsiders. The Ethereal can potentially be introduced here instead of the Overseer Crash Site.
- The player cannot choose which soldiers are used during the mission, nor their loadout. The top 5-6 soldiers available from the Barracks are automatically assigned to the mission; the player receives them equipped with whatever they had when the mission starts. It is best to leave these top soldiers fully equipped between missions after completing the Alien Base Assault; players who frequently use the loadout command "Make all items available" should be especially wary.
- Note that the soldiers are received in order, beginning with the top 3. The 4th soldier will arrive within a turn or two, but the 5th and the 6th only arrive as reinforcement waves as the player suffers casualties; if soldiers or XCOM Base Security personnel are killed, a reinforcement wave will be sent after two turns. A player who does sufficiently well may never see their 6th soldier take to the battlefield. In other words, most of the fighting will typically be done by a player's top four soldiers. Players should plan accordingly.
- It is possible you can choose who your first three soldiers will start the fight and which one of the active troops will come as reinforcements. If you have the Psionics Lab ready, you can place whichever one of your top three soldiers into Psi-testing if you feel he/she may not fit your requirements and you would favor different soldiers then you can stop Psi-testing them after a successful defense. Another method is sending them on a Covert mission if you haven’t destroyed the EXALT HQ yet, provided they are not Heavies or MEC Troopers.
- Super Heavy Weapon Platforms cannot join the base defense. If one does not have enough soldiers, an additional XCOM Base Security personnel will be supplied in its stead.
- Enemy types seem to depend on rank of your top soldiers. Dismissing all but 2 colonels resulted in 4 Sectoids popping on 2nd turn instead of 4 Sectoid Commanders. Classic difficulty, Base Defense on August 8.
- This mission supplements the player's regular soldiers with XCOM Base Security personnel; these soldiers are distinguished by their cyan armor and caps, and are functionally Rookies with default equipment and reduced stats (-10 Will and -1 HP). The player will start the mission with 3-4 of them and receives between 0-3 with each reinforcement wave. The game will never let the unit count exceed eight player units. Reinforcement teams will only ever contain one soldier; any other "free slots" will be filled by Base Security personnel.
- XCOM Base Security personnel can be considered highly expendable as the player will never see them again nor will they be listed on the Memorial Wall should they die. Due to their basic equipment and lack of special skills, they are most suitable for drawing fire and throwing grenades. Because of their weakness in combat, some players may want to actively let their Base Security personnel get killed, in order for them to be replaced with soldiers.
- Researching Tactical Rigging allows each of the Base Security personnel to start with two grenades.
- Getting at least 4 kills with the Base Security personnel awards the "All Hands on Deck" achievement.
- The first enemy units drop directly into the starting room (the Command Center) with the player's initial soldiers and Base Security personnel. The second wave consists of only alien units that can fly and they arrive outside the Rear Guard Station, the small building/room overlooking the cavern area adjacent to the Command Center. All the remaining enemy waves will come from the areas on the other side of the Command Center; enemies will drop into the Mech Bay and the Forward Access Tunnel, while the final wave breaches the gates of the Forward Guard Station.
- The alien waves seem to spawn at predetermined turns, regardless of the number of aliens still alive. A player taking too long at dispatching the alien invaders may find him/herself overwhelmed eventually, especially on higher difficulty levels. Make sure your soldiers deal as much damage as possible right from the start. It can also be worthwhile to sacrifice XCOM base personnel in order to activate reinforcements as early as possible.
- This is the only mission in which all alien forces will actively converge on the location of the player's soldiers. Even with only basic gear, this mission can be made extremely easy by positioning all soldiers on the second floor of the Command Center and placing them on Overwatch outside of alien Line of Sight. With no visible soldiers to attack, the alien forces will trickle into the room moving towards the globe projection, allowing XCOM to mow them down one by one. This strategy is highly advised on Ironman, especially on higher difficulties and/or when using basic gear.
The following status updates are received from Central Officer Bradford during the mission:
|Event or Condition||Update|
|Mission begins||"Delta section report. Delta section...report! ...Finally! Delta Section - it looks like your emergency generators are back online and... oh shh...! Delta, whatever this attack is, you're right in the crosshairs! We've got perimeter alerts triggering from all sides. It looks like you've got flyers coming in through the cavern near the guard station... Plus you've got a whole wall of heat signatures coming down through the vents in the ceiling above you."|
|"Whoever breached our internal security locked down the door systems separating you from the rest of the base. Once we get the doors open again, we can start sending reinforcements through, but that might take some time. Right now it looks like the closest alarms being triggered are in the vents above you - keep an eye out for any indications of movement. Delta Section - you have to hold the line. The future of XCOM is counting on you."|
|Aliens arrive||"We're picking up activity in the ventilation system near the Mech Bay, Commander!"|
|"We're picking up airborne hostiles moving on the rear guard station Commander. I'm not sure the alien ground forces can reach that area - they may be limited to aerial units."|
|"Commander, we've got something moving in the vents near the Mech Bay!"|
|"Commander, we're picking up contacts through the forward access tunnel ventilation system."|
|"Commander! We're picking up a steady increase in alien activity near the forward access tunnel... it looks like they're concentrating a force there. I'd get prepped."|
|"It looks like this is the last of 'em, Commander. We're not picking up any additional contacts - if we can take them out, HQ will be secure."|
|Area clear||"We're not picking up any additional contacts near the Command Center... I think you've cleared that area out, Commander."|
|"We've got zero new contacts near the Mech Bay, Commander - we should probably focus our efforts elsewhere."|
|Reinforcements imminent||"Commander - we've almost got the auxiliary power banks charged and I should be able to get one of the interior blast doors open - I'll send as many reinforcements through as I can before the charge dissipates and the door locks down again."|
|"Commander, I've got the auxiliary power banks spooling up now - once they reach a full charge the doors will open and I'll send another group of reinforcements through."|
|Reinforcements arrive||"You've got fresh reinforcements standing by, Commander. The bad news is we drained the auxiliary power banks while holding the doors open - it's going to take some time to reroute power for another attempt."|
|"We've got more reinforcements awaiting orders, Commander. As soon as the power banks spool up again, I'll send another group through."|
|"Reinforcements have arrived, Commander - this is the last group I can send through."|
|Mission complete||"We made a statement here today, Commander - they came after us, our people, right at the heart of our operation - and we showed them what happens. Now I think it's time we take the fight back to them."|
This mission serves to advance the main plotline and offers only the Star of Terra medal as a reward, in addition to any recovered alien corpses, weapon fragments or any captured aliens (and weapons).
Completing this mission awards the "They Shall Not Pass" achievement.
- Like the Temple Ship Assault, failing the mission permits the player to try again with a new RNG seed, even on Ironman mode. Some may consider restarting after a failed mission to be compromising a save's Ironman status, though the game itself does not.
- If a Base Security officer is killed by a Chryssalid and turns into a Zombie the game will often crash during the "Zombie pukes" animation.
- An unknown bug causes no aliens to spawn during the mission. This causes the mission to have no way of completion. Killing your team with explosives allows you to then restart the mission.
- In the patched PS3 version of the game, the screen goes black and you can't do anything. As this is an essential mission, it effectively ends your campaign. See https://www.youtube.com/watch?v=y8hUXCeJMkw for an example. The only way to fix the bug is to reinstall the game without the patch.
- An amusing bug can occur when an Ethereal is captured during this mission. It can be interrogated and dissected as normal, but the scripted dialogue will still describe the Ethereal encountered at the Overseer UFO as "unlike anything we've previously identified".
- A section of wall, just above where reinforcements come from, that looks over the mec-bay is glitched and can randomly teleport a soldier taking cover on that wall to the outside, on the balcony, potentially exposing them to enemy fire.
- SHIV's cannot spawn naturally on base defense. Even if the barracks contains no human soldiers. Instead, your reinforcements will consist of three generic recruits.
- SHIV's that are under repairs from a previous mission can spawn on base defense in their damaged state.
- The name of the mission is taken from Lays of Ancient Rome by Thomas Babington Macaulay, from an often quoted passage: Then out spoke brave Horatius, the Captain of the Gate:
"To every man upon this earth
Death cometh soon or late.
And how can man die better
Than facing fearful odds,
For the ashes of his fathers,
And the temples of his Gods."
- It is widely believed that the failure of this mission is what leads to the events of XCOM 2, as the Commander was apparently captured when the Alien forces attacked the XCOM base. Bradford and Shen's dialogue during their respective sections of the story support the theory. During the Tactical Legacy Pack, Bradford notes that XCOM HQ is a grave for a large number of the organization's personnel, and that he survived by crawling his way out of the base's ruins. In Shen's Last Gift, Dr Raymond Shen notes that reports compiled in the wake of the attack and the kidnapping of the Commander indicate that XCOM will be unable to hold the facility for much longer.
- DefaultGameData.ini. Game file. XCOM: Enemy Within. 2013.
|XCOM: Enemy Unknown Missions|
|Alien||Abduction • Terror Site • UFO Crash Site • UFO Landing Site|
|Council||Asset Recovery • Bomb Disposal • Site Recon • Target Escort • Target Extraction|
|DLC||Slingshot: Friends In Low Places • Confounding Light • Gangplank • Progeny: Portent • Deluge • Furies|
|Storyline||Alien Base Assault • XCOM Base Defense • Overseer Crash Site • Temple Ship Assault|
|Other||Starter Mission • Tutorial • Meld Tutorial • Covert Operations • EXALT Base Raid|