If you are in the game, just press `. Now you can enter the following codes:
iwillsurvive -godmode
takeittothelimit -unlimited ammo
hitmewithyourbestshot -hard mode
raindropskeepfallinonmyhead - you can call 5 airstrikes
Invisibility
Hit the ~ and type: closetoyou and the enemy wont see you.
Reduced Sky Details
While playing, press tilde (~) to call up the console window, then type "sky" and press ENTER. This speeds up the game and makes the world appear brighter.
Level Select
While playing, press tilde (~) to call up the console window, then type "letmego" and press ENTER.