At the indicated screen, hold L-Shift and press Keypad Minus. Then type any of the following "Codes":

Code - Effect

savegame - Saves Game (Gameplay)
endmission - End Mission (Gameplay)
campaign - Unlock Levels (Main Menu)
topographiy - ??? (Gameplay)
Iwillbetheone - God Mode

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