Complete the following tasks to unlock cheat codes. You cannot use these unless you have unlocked them first. You can use already unlocked cheats to make things easier.

Bulletproof --> Complete England Time Trial in under 27:00
Draw Enemy Health --> Complete Bolivia Time Trial in under 12:30
Infinite Assault Rifle Ammo --> Complete Japan Time Trial in under 12:15
Infinite Grenade Launcher Ammo --> Complete Kazakhstan Time Trial in under 27:10
Infinite Shotgun Ammo --> Complete Ghana Time Trial in under 20:00
Infinite SMG Ammo --> Complete Peru Time Trial in under 21:30
One Shot Kill --> Complete Bolivia Redux Time Trial in under 4:15
Textureless Mode --> Complete the game
Wield Excalibur --> Complete Nepal Time Trial in under 13:40
Wield Soul Reaver --> Achieve 100% Completion