As reported by an overwhelming number of persons, this game was ruined by setting the difficulty much too high.
Obviously, someone must have fixed it, or the honest folks at Gog would not
be selling it.
Where is the mod that allows a player to adjust game speed?

I'm not sure about any speed mods but have you considered trying some turn based games like jagged alliance 2? Game speed would no longer be an issue and you could do what you wish at your own pace.

Thank you for the suggestion. Yes, I've tried many turn-based games.
This game desperately needs an adjustable speed scale, such as the one in "Original War".
There is nothing fun about a game that has things going on where you cannot see them or react to them until it is too late. Frantic and frustrating are NOT fun.
The designers have made the commands to individual units very complex in this game.
There are many steps and mouse clicks and menus required......that calls for the game to also have the ability to slow down or pause while those commands are being issued.

If you hit backspace <-- key it opens a speed control and you can range from very fast 5 to very slow 1