For cheats in this game, use the DOS utility DEBUG.  First
 backup your game to be edited, then type the following from
 the dos prompt:

 ren e:\dr.exe cheater.cht
 debug e:\cheater.cht
 For infinate missiles, type: e37a3 90 90 90 90
 e3e71 90 90 90 90
 For invulnerability, type: e2dbc 90
 e 34ca 90 90 90 90
 e 344b 90 90 90 90
 w
 q

 Then rename CHEATER.CHT back to its previous name.