While the majority of rules in Call of Duty are almost identical to those in other d20 games. However, there are a few fields in which rules have been changed, adjusted, or added to. These are described below.

Modern Combat
   Combat is perhaps the area where the most changes have been made. With the advent of firearms and modern combat strategies, Combat has taken a turn away from hack and slash, and towards strategy. Check out this document to get the new maneuvers and abilities open to characters in Call of Duty.

Wounds & Damage
   To reflect the lethality of modern combat and the real world, a modified system is needed to handle damage in Call of Duty. Not only does this document detail thew new Vitality/Wound point system, it also gives information on optional rules for bleeding and stun damage. While mostly optional rules, it does have info essential to any campaign.