Press ~ to go to the console, then enter the following cheats followed by ENTER

Code - Result
/ammo - Unlimited Ammo
/winmission - Win Mission
/losemission - Lose Mission
/hitlermode - Hitler Mode
/fovs - Enemy FOV Rendering
/cheatcheat - Activate Cheat Mode
/ac - God Mode, Unlimited Ammo, Fly
/godmode - God Mode
/invis - Invisibility
/fly - Fly Mode