This mode is unlocked when you complete the Single-Player campaign on either the 'Casual' or 'Veteran' settings. In this mode ALL HUD elements are disabled and there is no crosshair to assist your aim. To make matters worse the enemies are a lot more accurate.
Go in the menu to the section enter code To get two extra multiplayer characters enter: 19NKXA8FLD For an exclusive finder enter: 4V35JZHQD6 And now for the best one,to get all the recon reports enter: 0ZNDRBICRA and get four achievements for 70 points extra!!!
Just a hint,before the Z in the code,comes a zero 0 not an O,just so it works.