This cheat will give you unlimited ships in the game.

 [CGA]
 Make sure "CGASHOOT.EXE" is in your current sub-directory,
 then type from the DOS prompt:

 ren cgashoot.exe cgashoot.cht
 debug cgashoot.cht
 e 6da e9 10 1
 w
 q

 ren cgashoot.cht cgashoot.exe

 [EGA]
 Make sure "EGASHOOT.EXE" is in your current sub-directory,
 then type from the DOS prompt:

 ren egashoot.exe egashoot.cht

 debug egashoot.cht
 e 70b eb 7
 w
 q

 ren egashoot.cht egashoot.exe