Holdridge, USMC (ret), details modern, hypothetical combat between U.S. troops versus the OPFOR who are armed with various equipment from across the globe.

Later additions added units for the Canadian, Australian and New Zealand armies, and the US Marines.

The game is noted for its encyclopedic array of modern arms and units, and the detailing of the combat.

During a combat phase these orders are executed and the player can only watch the results as 60 seconds of game time passes.

A combat phase represents 60 seconds, and is typically divided into four 15-second segments in which units fire and move.