Apogee Software generously released this game as freeware in March 2006.
NOTE: This game uses a DOS installer. For details on how to install a game in DOSBox, please check this tutorial.
The cheats here are a bit more complicated than in other games. There is a two step procedure to active the cheat mode. This cheat mode only works in the registered version. It does nothing in the shareware version.
Type [C] [H] [E] [A] [T] at the Main Title Screen. All keys need to be pressed one at a time. When you get it, you'll see the message that says "Cheat Active" (it really isn't yet).
During the game, hold down then [backspace] key, and then press
the [H] & [S] keys at the same time. When you are successful, you'll see a message that says "Cheat Mode On" (it is now). You can hit these three keys again to turn the cheat mode off.
Once activated, you can press these keys to activate various options. Please note that you must hold down the [tab] key first before pressing the others, or it won't work.
[tab] [O] - Fire options
[tab] [R] - Rapid fire
[tab] [S] - Shield options
Description by MobyGames