As stated Above, this should unlock after the 6th mission. There is a bug right now that prevents the achievement tracker and in game stats from going up. The only solution i have right now is, Basically you have to finish each level through to the end without closing the game or leaving. each time i load up Crysis, I just go to campaign and pick the latest level I am on and finish it. If you die during the level, loading the previous checkpoint seems to be fine. the tracker will go up and the in game stats of missions completed will reflect correctly.