During the game, hit the tilde key (~) to bring down the console. Now type the following codes and press enter to activate them.

Code - Effect

/losemission - Loses the current mission
/winmission - Wins the current mission
/cheatcheat - Activate all the cheats
/ac - God mode, infinite ammo, zero gravity mode
/godmode - Invincibility
/ammo - Infinite ammo
/invis - Invisibility
/fly - Zero gravity mode
/fovs - Toggle field of view for enemies
/hitlermode - Hitler mode
/arrival - Show/Hide arrival points
/astar - Show/Hide AStar paths