Hold down both [Ctrl] keys and press:

 [0]  -  Finish mission
 [1]  -  Invincibility
 [2]  -  Unlimited torpedoes
 [3]  -  Unlimited cannon ammo

 Here we do a little editing, but not hex editing. All you need is
 the notepad and a saved game that you will find in
 Bluebyte\AD\Dat\Save.  Then open the saved games until you find the
 one you want.  For example: if you want to edit a saved game you
 named "Floodgate" open that saved game and the first 3 lines will
 read:

 [Global]
 Name = Floodgate
 Credit = 13237 <- this line shows how many credits you currently have

 You can change this line i.e.
 Credit = 99999 <- you will now have $99,999 when you load this saved
 game. This is enough money to buy anything you want from any Arms
 Dealer.

 Attention: Don't change other figures than the money! This is not
 that easy and will crash your game.