Welcome to the underworld.
—The Irkalla before "singing" the deaths of her enemies
The Aerial Fortress Irkalla is the epic unit of Epsilon Headquarters, acting as a "one-man army" capable of single-handedly annihilating ground and air targets alike.
With the advent of the Soviet built Centurion Siege Crawler,[note 1] for the first time, Yuri’s grasp for power was legitimately challenged. A machine that could absorb and deal great damage, as well as being immune to psychic trickery, could prove to be Epsilon’s undoing.
Therefore, deep within the bowels of the Epsilon Headquarter’s[sic] hangars, a weapon of massive proportions was being built. A weapon capable of not only providing Headquarter’s armies with massive firepower, but defend Yuri’s ultimate weapon as well.
Since its devastating first appearance, the flying war machine codenamed "Irkalla" has become a symbol of Yuri’s utter dominance over his enemies. Practically, the Aerial Fortress Irkalla is Epsilon’s ace in the hole: capable of engaging multiple targets in the air and lay waste upon ground targets. Since its deployment, no Allied or Soviet force alone has been able to set foot on Antarctica.[note 2]
The Irkalla makes a Headquarters base a difficult feat to destroy once it is deployed, as its weapons are able to eliminate any unit on the battlefield swiftly, whether it be infantry, vehicle or aircraft. While it is possible to outrun the Irkalla with faster units or fool it with infiltrators and rogue stealth units, its long range weapons, as well as their Imploders' tendency to pursue enemy forces until it finally hits their targets, make the Irkalla one of the most, if not the most effective one-unit defender that does not have the ridiculous power consumption or the inability to defend against air threats of the Plasmerizer.
However, even an epic unit has its own flaws. The high cost and tech requirement meant that HQ's enemies wouldn't have to worry about an oncoming presence of an Irkalla until Epsilon HQ has reached Tier 3. Even if said subfaction is able to construct an Aerial Fortress Irkalla, its enemies would have already amassed a large amount of forces with heavy anti-air support at the ready by the time the Irkalla reaches the enemy base. Combined with the Irkalla's slow Imploder speed and its own speed, it is possible to overwhelm an Irkalla with sheer force.
It is also worth noting that the Irkalla is unable to use its imploders against air units, which means Thor Gunships, Alanqa Skystations or just plenty of anti-air aerial units are capable of destroying an Irkalla without suffering as much casualties as land troops doing the same.
Though hardly noticeable because of the rapid firing rate, the Irkalla follows a specific pattern when firing. The exact order is the following:
- Dissolver beam
- Imploder (x4)
- Repeat cycle.
As mentioned before, the Irkalla will not fire imploders when attacking air units.
On hard difficulty, the AI occasionally builds Irkalla targeting player's nearest building.
- The first Irkalla appears in Godsend where it is chronoshifted, carrying a group of elite Initiates and Epsilon Elites, into the European Alliance's fortress-city of London to cause destruction as it makes its way to the SteinsTech Hangar. In this mission, the Irkalla must not be destroyed and also serves the role of radar: if its health falls under 33%, radar will be disabled until its HP rises past this threshold, and shroud will also be reset. It is destroyed when the Paradox Engine makes its escape.
- The first objective of Meltdown involves using Chitzkoi (who has been upgraded with Chinese tech) to capture an inactive Irkalla so the Psychic Dominator in the area could be destroyed. Once Chitzkoi enters the Irkalla, it'll be called Chitzkalla and fall under control of the player, using Chitzkoi's voiceset. The Irkalla must not be destroyed during the mission.
- In Insomnia, after the Paradox Engine arrives with a wing of Thor Gunships, the enemy Epsilon will send an Irkalla against them, to predictable results.
- In Unthinkable, one Irkalla is initially given to the player, and another one later in the mission.
- In the Ascension Challenge, immediately after the game begins, an Irkalla will spawn from the top edge and head towards the challengers' starting point. Afterwards, two Irkallas each are a part of the Headquarters' Golden Armada, accompanied by 12 Basilisks and 7 Salamanders, all of them appearing from the central point on the top edge of the map, then proceed towards the south where the players' bases are located. Each of the Radar Spires that can be destroyed in order to delay the Golden Armada is also guarded by an Irkalla.
- In Mesopotamian mythology, Irkalla is a place on Earth from which there is no return, or the underworld where the dead exists after death.
- The Aerial Fortress Irkalla bears close resemblance to the Leviathan from Tiberian Twilight.
- The Aerial Fortress Irkalla's unit ID in the game files, [GOTTER], is a reference to the giant space battleship Götterdämmerung from the movie Iron Sky, named after the German translation of Ragnarök, "Twilight of the Gods".