Green Storm is the name of a protocol used by Steve. When it is activated, he assumes direct control of one or more people through their shock implant. This control is so total that he can even use brain implants like psychokinetic amplifiers or Solid Light Generators. The protocol is intended to be a last-ditch, emergency response to a situation in which all team cohesion has been lost and a total party wipe seems imminent; it has been used only once, so far, against an Arbiter of Peace.
It was originally a secret between the Generals and Steve, but was revealed to the main body of ARM before Mission 26. It caused an uproar, and almost caused a revolt. A compromise was eventually reached wherein it was possible to opt-out of the protocol. (After Steve initially told Lars to cut off the hand of anyone who raised one to indicate they objected to Green Storm.)