Command, Control, Communications and Intelligence. Now occasionally referred to as C4I, the extra C standing for Computers. Can either be an adjective, in which case it describes the nature of a system, or a noun, in which case it refers to the complete structure set up for this purpose (usually by a nation). Typically, C3I systems refer to military systems and/or organizations. For a good explanation of this type of system and how it relates to nuclear war, see Bruce Blair, Strategic Command and Control, the Brookings Institution, Washington D.C., sometime in the 1980s.