A power generation system based on the supersolenoid theory advocated by Dr.Katsuragi (Misato's father). When EVA is loaded with this engine, its active time could be extended to infinity. All Angels possess this S2 Engine, and EVA 01 got it when it devoured the 14th Angel.
Moreover, all EVA's from EVA 05 onwards also possess this engine and thus do not need Umbilical Cable any more. EVA 04 was testing a similar system when it blew up at NERV's headquarters in Nevada, USA.