In-Game Cheats
     To  unlock  the  following,  you must beat the respective tour of
duty (US, Canada and Britain).

Unlockable              How to Unlock
Unlimited Ammo          Beat the game on the Green Difficulty
Unlimited Health        Beat the game on the Hardened Difficulty
Unlimited Grenades      Beat the game on the Veteran Diffculty

How to unlock Survival! Mode
     It will only work if you select the Difficulty Hardened. Once you
do  this,  your  save of Hardened will be no more. It will not work on
Green or Veteran.

Unlockable              How to Unlock
Survival! Mode          Play and beat the game on Hardened Mode, 
                        then it will ask if you want to switch to 
                        survival mode. Select yes and it will switch to 
                        Survival Mode.