Put all cheats in at the pause menu during the game.

When entering the cheats, hold LT+RT+back while entering the following codes...

All Levels Unlocked
Y, RB, Y, RB, X

Note: this code is input at the mission select screen, the rest are input during gameplay.

Health at 100%
LB, LB, RB, X, RB, Y

Unlimited Ammo
RB, RB, LB, X, LB, Y

Team is Invincible
X, X, Y, RB, Y, LB

Scott Mitchell is Invincible
Y, Y, X, RB, X, LB

Make Soldiers Tiny
LB, Y, Y, X, LB, RB

More Cheats Coming Soon...