Level select
Press X, Triangle, Up, Left, Square at the start menu.

Unlimited Ammo:
Successfully complete the game under the Green difficulty setting to unlock this cheat for the Tour of Duty that was played. Alternately, successfully complete the game with all Bronze medals.

Unlimited Grenades:
Successfully complete the game under the Veteran difficulty setting to unlock this cheat for the Tour of Duty that was played. Alternately, successfully complete the game with all Silver Medals.

Unlimited Health:
Successfully complete the game under the Hardened difficulty setting to unlock this cheat for the Tour of Duty that was played. Alternately, successfully complete the game with all Gold Medals.

Survival Mode:
Successfully completed the game under the Hardened difficulty setting. You will be prompted to enter Survival mode.