I don't know how the system works without referees, but when referees are present, they travel with squads, groups, weapons teams, etc. The referees will not tell an individual to take a hit. However, they will record instances where somebody
should take a hit, and if they don't, there is a point reduction or some other sort of penalty. Its explained in better detail here,
Rules for the GCS Combat System.
Not an accurate system if you ask me, but its all they have to go with so far. I watched this wargame show one time where they used a sort of laser tag system for getting hit. Everyone wore a vest, and every gun had a laser attatched to it. When they would fire blank rounds, they would also shoot a laser out. If the laser hit the vest, it would start beeping, indicating a hit. I forgot the name of the system, but if WWII reenactors would adopt it, it would add a whole new level of realism, but thats just my 2 cents.
