Jet Alone is a bipedal robot developed by Japan Heavy Chemical Industries, designed to supplant the Evangelions. Unlike the Evangelions, which have a limited internal power supply and must rely on external power cables for extended operation, Jet Alone has an internal nuclear reactor (likely a pressurised water reactor) and can function for at least 150 consecutive days. Jet Alone also requires no pilot, and is controlled by an onboard computer. Radio commands can be issued from a ground station.
Being a robot and not a living being, Jet Alone cannot generate an A.T. Field. Tokita, the head of the J.A. project, pushes aside the issue, describing the creation of an (artificial) A.T. Field as "only a matter of time."
Jet Alone appears in episode 7, where J.H.C.I. have prepared a activation test to show off their new weapon to possible sponsors and weapons contractors in Old Tokyo. The activation test was sabotaged by Gendo, resulting in Jet Alone losing control, turning it into a walking nuclear meltdown waiting to happen. J.A. heads straight for the city of Atsugi.
Misato at this point describes J.A. "as badly behaved as the guy who built it!"
As the radio command circuit had been broken Misato had to manually insert the password, HOPE, to wipe out all of J.A.'s programming in order to stop the meltdown. The password fails and Misato attempts to push the control rods back into J.A.'s reactor herself, which at the last moment reinsert themselves. This reveals to Misato and the audience that J.A. was never intended to meltdown. Gendo simply intended for J.H.C.I. to lose face so their project couldn't threaten the continuance of Project E.
Jet Alone was named after Jet Jaguar, Godzilla's robot sidekick from Godzilla vs. Megalon. In an early draft of the Megalon script, Jet Jaguar was named Red Alone and Jet Jaguar was made from submissions from the public which he was set to star in a film vehicle for him titled "Jet Jaguar: Fighter of the Planet" which pitted him against Megalon (a previously unused Godzilla monster design at the time) before Godzilla and Gigan where added due to marquee value. The Gainax staff took the first half of the final name and the second half of the preliminary name to make the name Jet Alone and Jet Alone also has a grill on its head that is meant to resemble Jet Jaguar mouth.