Cheat mode:
Press [F1] during game play to display the help screen. Then, enter one of the following codes to activate the corresponding cheat function:

Effect        Code 
Unlimited ammunition [Ctrl] + M  
Invisibility [Ctrl] + X  
Invincibility [Ctrl] + I  
Mission skip [Ctrl] + H  

Mission select:
Type hossana at the mission selection screen to unlock all missions.