While playing a game in single player mode, press [Shift] + C to activate the chat function. Enter one of the following codes, then press [Esc] to end chat and activate the corresponding cheat function:

Code - Effect

BigAssShields - Invincibility
WonderWoman - Invisibility
ShootEmUp - Infinite ammo
GoingAndGoing - Infinite fuel
IamTheMaster - Mission completed
DieDieDie - Kill target