These are the various DEFCON levels of the game.
“DEFCON 1 is the threat level at which Nuclear Missiles can be fired, they can be ICBMs, MRBMs or...DEFCON 1
“DEFCON 2 has the same combat restrictions as DEFCON 3. During this stage it is common to launch...DEFCON 2
“DEFCON 3 is the DEFCON level where hostilities begin. No nuclear missiles may be fired or armed...DEFCON 3
“At this stage of the game, Radars and other buildings activate and reveal other buildings or...DEFCON 4