A war game is any form of simulation designed to prepare a force for war. In this respect practising drill was a form of war game for 19th Century armies and even simple activities such as practice on a firing range fall under this umbrella. Some war games may take the form of a board game with dice rolls and complicated calculations, others may be simulated by computers with network linked simulators fighting a virtual battle and large formations will even take part in live firing exercises over vast training areas with a team of umpires to adjudicate. In Acts of War Richard Holmes recalls leading a platoon on an assault of a enemy position during an exercise on Salisbury Plain only to be told by an umpire that he, and a number of his men, were “dead” and could take no further part in the exercise.

Probably the most successful use of war games in the 20th Century is that of the German Army in the development of armoured warfare and the invasion of France in 1940. Prevented from building a large, armoured force by the Treaty of Versaille, the Wehrmacht developed its doctrine on paper and then tested it in exercises, often using simulated tanks in the absence of the real thing. These exercises enabled to them to experiment with many different methods leading to the armoured doctrine they eventually used as well as advanced methods of co-ordinating fire support from artillery and the Luftwaffe with the development of tactical and sub-tactical radio communications.

In the run up to the invasion of France, the Wehrmacht conducted detailed exercises based on practising for specific elements of Fall Gelb. Realism was strictly enforced with Heinz Guderian berating some of his soldiers for enjoying themselves too much whilst rowing a canoe over a river used to simulate the Meuse. The line he used “Joy riding in canoes on the Meuse is forbidden!”, was thrown back at him by one of his commanders when he crossed the Meuse in anger during the real operation. With everything going to plan, Guderian obviously looked like he was having a bit too much fun!

References

Corum, J. The Roots of Blitzkrieg: Hans von Seekt and German Military Reform.

Guderian, H. Panzer Leader.

Holmes, R. Acts of War.

The other example I would cite where the American Fleet Problems in the pre World War II era. The fleet problems where war games where a force (usually identified by colors, but sometimes representing more realistic opponents such as the Americans, British or Japanese) attempted some tactic of war, such as attacking Panama (Fleet Problem 9). Both of these delivered warnings that the US later forgot - exactly how difficult it was to stop a carrier fleet and the primacy of massed airborne first strike.

Sneak attacks on Pearl Harbor where constant themes of these engagements. The Fleet problems where designed by the fleet at sea, rather then official war games in Washington, and it's striking how often the admirals adopted strategies and tactics that would later occur in reality.

In addition to the failed lessons, some positive lessons where learned. Using the aircraft carrier as independent attack forces, rather then screening forces for larger fleets was one outcome of the Fleet problem. This principle played a huge role in the battle of midway, where this principle and the desperate need to successfully land the first blow were instrumental.