Kriegsspiel ('war-game') was introduced in 1824 by Lieutenant von Reiszwitz of the Prussian army, after several years spent in perfecting the game as originally designed by his father. It aims at giving interesting representations of military manoeuvres on a contoured map of sufficiently large scale to show all the features of the ground, and enable their effect for cover, command, or concealment to be duly allowed for. The troops are represented by metal blocks coloured red for one player and blue for the other, and made to the same scale as the map. One officer takes command of each side, assisted, if necessary, by subordinate officers. An umpire, with generally two assistants, superintends the game. A 'general idea' of the military situation is issued to each side, and contains whatever information it is considered probable that each would have under the circumstances. A 'special idea' follows, giving such details as the strength and composition of each force, its distribution at the commencement of the game, the immediate object in view, the date and hour of the imaginary time at which operations commence, and any information as to the enemy which may be in the possession of the commander-in-chief, represented by the framer of the scheme. The 'special idea' for one player will differ from that for the other, and must not be seen by him. The wind, weather, state of the country, &c. are usually assumed to be as on the day of playing.
Each player then frames his orders, and is strictly held to them. Three copies of the map are generally used, though one is enough if the players are only allowed access to it in turn when the other's troops are covered up. On 'red's' map, if three are available, only his own troops are shown, until, as the game progresses, it is decided by the umpire that he could see some of 'blue's' men, when pieces representing those only which are so seen are placed on it. 'Blue's' map is similarly treated, but on the third, or umpire's map, both sides are completely represented. The game proceeds by moves, each of two minutes' imaginary time, the space the different arms would cover in that time at ordinary marching rate being laid down on a scale, and thereby transferred to the map. The player points out the direction in which he wishes each body of men moved, and the assistant umpire then measures off the distance and places them. The same number of moves is given simultaneously to both players, and the number of moves given at a time grow less as they come nearer, until perhaps only half a move can be given, or the question arises whether any advance can be made on one side or the other. This and all similar points must either be decided by the umpire from a consideration of the situation, or by a throw of the die. Rules are laid down for the guidance of umpires: thus, 'repulsed' troops cannot come into action again for ten minutes (five moves), 'defeated' troops cannot do so for twenty minutes, and if 'totally defeated' are removed from the map. The victorious side loses half as many as the 're- pulsed' or 'defeated,' and one-third as many as the 'totally defeated' troops. If the die is used a table of possibility decides such questions as 'can guns come into action under infantry fire,' the odds being 3:2 in favour of the infantry at 500 yards; 2:1 at 400, and so on. These odds also determine the loss per battalion or squadron by means of another table, which allots certain faces of the die to either colour, and regulates the loss in proportion to the number of dots on the face which turns up. Thus, in a question where the odds were 5:1 against 'red,' if the single dot turned up, 'blue' would be 'repulsed' with a loss of six per battalion; if two, three, or four dots turned up, 'red' would be 'defeated' with losses of eight, nine, or eleven per battalion; and if five or six dots turned up, 'totally defeated' with losses of fifteen and eighteen per battalion. Tables of losses from artillery fire and infantry fire at various ranges, and under different conditions are also used, and the time required for destroying or constructing bridges, &c. laid down.
Intelligence of the enemy, if seen by a scout, is obtained from the umpire, who allows himself to be questioned, but frames his answers in accordance with what the scout would be likely to know. Orders sent to detached bodies of troops cannot take effect until sufficient time has elapsed for an orderly to reach them; and, if directed to go across country, at each fence the die must be thrown to decide whether he gets over without a fall. Everything is done to make the conditions of the game similar to those of actual warfare, with the result that the players cannot fail to realise the value of time in military operations, the difficulty of ascertaining the enemy's movements, and the necessity for clear and definite orders. The umpire decides when the game shall cease, which is generally when one side has clearly obtained the mastery or gained his object. See Vernois, The Tactical War Game (trans. by Macdonnell, 1884).