"Disposing of the Angel on the surface is so expensive!"
An A.T. Field (short for "Absolute Terror Field") is a nearly impenetrable force-field barrier which Angels and Evangelions can generate. Conventional weapons are effectively useless in penetrating an A.T. Field; the only thing that do so is another A.T. Field, such as those created by the Evangelions. Additionally, it can be breached by using a directed-energy weapon such as the Positron Cannon from Episode 6.
Properties of an A.T. Field
Typically, A.T. Fields are invisible. They can interact with objects to cause them to move, and it is hypothesized that they are the source of some of the Angel's ability to levitate (most notably, Kaworu and Sachiel.) The A.T. Field can create air distortion when activated as seen in Episode 03, when Evangelion Unit-01 raises its A.T. Field. The same effect is visible during the fight between Evangelion Unit-01 and the Kaworu-Controlled Unit-02. The field becomes visible when it violently collides with anything else, forming concentric octagonal yellow lines. This can be seen in Episode 02 when Evangelion Unit-01 collides with Sachiel's A.T. Field. It is also seen in Episode 22 when Arael's A.T. Field deflects a blast from a positron rifle.
Although A.T. Fields were at first seen to be a purely defensive ability, it is demonstrated throughout the series that A.T. Fields can be used in an offensive fashion. The first instance of this was when the Angel Sahaquiel used its A.T. Field in Episode 12 to crush several nearby satellites attempting to observe it in Earth orbit. Leliel's bizarre multi-dimensional pocket-dimension is apparently created by inverting its A.T. Field in some way. Arael's mind-probe attack is based on a special projection of its A.T. Field. Eva-01 itself wielded its A.T. Field as a weapon in Episode 19 at the climax of the battle against the Angel Zeruel, projecting it to slice through the Angel's body and cripple it. By Eva 02's final battle in The End of Evangelion, Asuka's piloting abilities had increased to the point that she offensively wielded Eva-02's A.T. Field against advancing JSSDF hoverjet squadrons and tank battalions.
Later in the series, Kaworu Nagisa reveals that every living thing possesses an A.T. Field: Angels and Evangelions just have A.T. Fields so strong that they are physically manifest. A.T. Fields which regular humans generate hold individual beings' egos together, separating individuals. Each Evangelion has a human soul inside it: A.T. Fields are generated by the human soul contained within the Eva. The A.T. Field of an Angel is also generated specifically by the Angel's soul.
A.T. Fields and Anti A.T. Fields
In the climax of The End of Evangelion, the Rei/Adam/Lilith hyper-being generates, along with the Mass Production Evangelions and Evangelion Unit-01, a massive "Anti A.T. Field" which neutralizes all A.T. Fields across the world, causing all of humanity to revert into the primordial soup of LCL, merging into a single super-organism in the climax of the Human Instrumentality Project.
Destroying an A.T. Field
The easiest way to destroy an A.T. Field is to essentially counter it with another A.T. Field, as demonstrated by the Evas on several occasions. An example of this is seen in Episode 1, when the berserk Unit-01 corrodes Sachiel's A.T. Field in battle.
Besides Evangelions, only two human-made weapons are capable of effect against Angels. The first is the N² Mine, the most powerful non-nuclear weapons ever created. N² mines have succeeded at stunning or even seriously injuring some of the weaker Angels (albeit temporarily because wounded Angels have always regenerated), but against some of the more powerful Angels, even multiple N² mines have failed to do any damage whatsoever.
There was one other instance where an A.T. Field was breached without the use of the Evas, the fight against Ramiel, where a prototype positron rifle using the electricity of the entire power grid of Japan penetrated Ramiel's A.T. Field and killed the Angel. However, such a weapon is subject to power and range limitations, as witnessed in the battle against Arael where a positron rifle (of a different model from that used against Ramiel) failed to harm the orbiting Angel.
The one weapon practically capable of piercing any A.T. Field is the Spear of Longinus: an extraterrestrial artifact of incredible power, shaped like an Eva-sized javelin. Artificial replicas of the Spear of Longinus are also capable of piercing an A.T. Field.
Since the very earliest days of Evangelion analysis, there has been a rumor that A.T. Field is a genuine psychological term that describes the barrier that separates autism patients from the world around them. However, extensive searching of online psychology researches and forums has failed to find any use of the term other than in reference to NGE. Therefore, this rumor can safely be dismissed as false.
In the Rebuilds, the A.T. Fields present all of the same properties so far, and are once again used as weapons by the Evas.
In Evangelion 2.0 during the battle with Zeruel, the berserk Unit-01 turns its A.T. Field into a beam shot from its eyes.
In the same battle with Zeruel, Unit-01 creates an artificial arm with its A.T. Field, and uses it as a weapon, taking the form of a ring of geometric shapes which blast the angel back.
Notes & References
- The phrase "Absolute Terror Field" is never actually mentioned within the series itself. It only appears in the opening credits and during the fight against Sachiel in Evangelion: Death.
- Although when an A.T. Field is visible, it's usually concentric octagons. However, there are 2 instances where this is not the case. First, in Episode 06 when Nerv staff reviews an energy blast that deflects off of Ramiel's A.T. Field, it is seen as hexagons on the display, even though they were octagons earlier; this is a visual continuity error. The second instance is in Episode 13 when lasers were deflected by Ireul's A.T. Fields which were purple hexagons and were not concentric; this is most likely a reference to the movie The Andromeda Strain.
- A.T. Fields can oppose each other and act as a barrier to each other as well - Eva-01's A.T. Field blocks Sahaquiel's A.T. Field and keeps the Angel suspended in the air (although demanding a lot of physical strength from the Eva itself) before the other two Evas arrive.
- Ritsuko Akagi makes it a point that an Eva's A.T. Field "erodes" that of an Angel; most Nerv personnel tend to loosely refer to the process as one A.T. Field "neutralizing" or "canceling-out" the other.