Revenge Of Defender

Cheat mode:
Press [Space] during game play to display the options screen.
Highlight the "View Game Screen" option, then press Left + Fire on the Joystick.
The game screen will appear.
Release the joystick and press Fire.
The option screen will reappear.
Highlight the "Sound On/Off" option, then press Right + Fire on the Joystick.
Highlight the "View Game Screen" option again, then hold Right on the Joystick, hold the Right Mouse Button, and press the  Left Mouse Button.
The option screen should display "Cheat Mode" to confirm correct code entry.
Resume game play and press Fire for unlimited shields.
Any level can be selected from the options menu.