The Beyond the Barbed Wire material was created for use with the d20 Modern Roleplaying Game system of game mechanics. But can also be employed with the Dungeons & Dragons 3.5 Edition (d20SRD) rules as well.
This Rules Guide documentation provides a "cut down" version of the d20 Modern rules and game mechanics for your reference. Plus the "house Rules" we created that enchance the d20 Rules for this campaign enviroment.