Type oh dear at the main menu to enable the codes:
ALT-1 | Full ammo |
ALT-2 | Upgrade current weapon |
ALT-3 | Full energy |
ALT-4 | Invincibility |
ALT-5 | ??? |
ALT-6 | Complete mission |
ALT-7 | Deactivate enemies |
ALT-8 | Helicopter mode |
ALT-9 | Tank mode |
ALT-0 | Speed |