Following the completion of the prototype Unit 00, Unit 01 was developed as a test type model. However unlike Unit 00, Unit 01 was intended to be used for combat in order to collect data which can be seen from the pair of fins mounted on Unit 01's shoulders that store a pair of progressive knives.
Like Unit 00, Unit 01 relies on an external power source - in this case an umbilical cable - to operate for extended periods of time. In emergencies, or if the cable is damaged, Unit 01 can switch to its own internal battery. However, this internal battery only lasts for five minutes, meaning Unit 01 either must find another external source of power, or quickly withdraw from the battlefield. However, on rare occassions, Unit 01 is known to reactivate on its own, despite its own internal batter being depleted. During this time, Unit 01 goes completely berserk, its rage directed towards the target, where it will brutally rip apart the target until it is reduced to nothing more than a bloody mess. Much to Nerv's frustration, there is no known explanation for this phenomenon and therefore, no way to address this issue or weaponise it.
Due to going berserk on numerous occassions, even if it leads to destroying the target, Unit 01 has been deemed unreliable in terms of combat, something that cannot be afforded when it comes to combating Angels.
Rebuild of Evangelion
Its design remains largely the same, with some extra green highlights added throughout the body. In addition, Unit 01's progressive knife has been changed to a switch blade-style, where it is folded when stored in the shoulder fins, and unfolded when drawn for battle.
However, there are significant changes when it goes berserk. The green highlights change to red, and the purple seems to shift to a much darker shade. It has shown to display abilities comparable to the Angels, leading many to question the true nature of the Evangelions, especially Unit 01.
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