You haven't figured this out?!? Ok, at the end of a mission when you see the map thing and all the arrows flying around, on the side bar where it calculates points, rewards and what-not towards the top left corner of the screen your rank will be displayed. The rank changes as the map overview of the level progresses so if you want to see your rank right away press the start button once and everything that you did on the mission (kills, reward, rank, ect.) will be displayed