Hold [Left Shift] and press [Keypad Minus] at the indicated screen.
Release the keys, then type one of the following codes to activate the 
corresponding cheat function. 

Code  Result 
savegame    Saves Game (Gameplay Screen) 
endmission  End Mission (Gameplay Screen) 
campaign    Unlock Levels (Main Menu) 
topography Unknown Effect (Gameplay Screen) 


Infinite Save Games
If you need to save more than once in a mission, then you need to delete the 
old save game file. It can be found in the directory 
Users\\Saved\Campaigns\1985. ALT-TAB out of the game, make a backup copy 
(trust me!) and then delete the save file. ALT-TAB back and press ESC to pause 
the game. You should now be able to save the game again. You can do this as 
many times as you like.