Unlock all levels:
To unlock all levels, at the start menu, press X, Triangle, Up, Left, Square.
Survival mode:
Beat the game on the Hardened difficulty setting to unlock Survival mode.
Infinite health:
Beat the game on the Hardened difficulty setting to unlock the option for unlimited health for the Tour Of Duty that was played. Alternately, beat the game with all Gold medals.
Infinite ammo:
Beat the game on the Green difficulty setting to unlock the option for unlimited ammo for the Tour Of Duty that was played. Alternately, beat the game with all Bronze medals.
Infinite grenades:
Beat the game on the Veteran difficulty setting to unlock the option for unlimited grenades for the Tour Of Duty that was played. Alternately, beat the game with all Silver medals.