The U.S. Army has contracted to purchase up to $78 million a year (for the next five years) in technical services for its electronic wargaming facilities ("Constructive Training Systems" in milspeak.) These wargames allow commanders, subordinates and their staffs to play a computer simulation that accurately uses military equipment to carry out a military operation. The army has several dozen of these systems (for units from battalion to theater level), many of them portable. The maintenance has mostly to do with software and networks. Basically, these wargames are networked computers equipped to plug into the networks commanders would use in combat. The simulation software either uses artificial intelligence to provide an "enemy", or human "Red Force" commanders.
While this appears similar to some commercial wargames, the army versions are actually quite different. While a commander (and his staff) can "win" or "lose" a battle, that is not the main point of these exercises. The primary purpose of these Constructive Training Exercises is to make sure all the people in the headquarters know their jobs, and can carry out those jobs efficiently with the many other people they will have to work with in combat. Thus these wargames are simulation process, more than actual combat. Actually, some of the things headquarters people will be doing, like coordinating air or artillery strikes, or planning attacks by infantry or tank units, will involve actual combat. But to bring off any of these operations successfully requires that communications, maintenance, supply and other specialists do their jobs as well.
The Constructive Training Systems allow brigade staffs to test themselves several times a year, and smaller units, or groups of troops, as often as they like. This is particularly useful with there are new procedures, new equipment, new enemies or new tactics involved. Best to practice with the computer version of the battlefield, before you do it with real people and ammunition.
There are dozens of combat simulations available in the Department of Defense, but a few of them get most of the use. At the lowest level, we have JCATS (Joint Conflict and Tactical Simulation), which simulates individuals troops, vehicles and weapons (up to 60,000 of them) and can handle multiplayer, but can also run on a laptop for, say, a platoon level operation (like raiding a Taliban hideout or manning a checkpoint.) JCATS is very popular and generally handles wargaming up to the battalion level or brigade level. OneSAF (One Semi-Automated Force) is meant to replace JCATS, but the JCATS developer (Lawrence Livermore Labs) keeps upgrading their sim (which began as JANUS, three decades ago). Competition is good.
CBS (Corps Battle System) is for larger units (division, corps, and up) and is the game that allows dozens (or hundreds) of staff officers and subordinate commanders to train together. Some of these subordinate units would use JCATS, or more specialized sims (like for logistics or electronic warfare) to obtain results for decisions as CBS participants.
WARSIM (War Simulation) is meant to replace CBS, and is slowly doing that. But WARSIM was part of a billion dollar development boondoggle in the 1990s (the full name was WARSIM 2000), and developers are still picking up (and rearranging) the pieces from that mess.
Another problem area is the search for a wargame that will combine those used by the army, navy, and air force. The army and marines often use the same sims, at least while dealing with ground combat. But the navy and air force operate in a different environment, and when they have to account for what the army is up to, often use sims that have a different take on land warfare. This causes problems when all the services have to operate together, and efforts to resolve these differences continue.