Type "1982GONZO" during the game. (There is no zero in this cheat code).|
If that doesn't work, try "GONZO1982" instead.
Now, you have the following options:
SHIFT+V : Trace user.
SHIFT+X : Tele-transport. (place the selected commandos under your mouse cursor)
CTRL+I : You are invincible.
CTRL+SHIFT+N : Finish the mission.