The great 19th century German strategic theorist, von Clausewitz, was concerned not only with the ideal principles of strategy but with the many reasons that wartime plans go wrong in practice. He was in effect an early believer in what we now call Murphy's Law. He expressed something very close to it, with respect to the vast potential for human error, with his dictum that "any order that can be misunderstood will be misunderstood." In addition, he formulated two general concepts to explain why military results tend to fall short of the theoretically achievable: "friction," and the "fog of war." "Friction" refers to the innumerable incidents, often individually small, that collectively serve to reduce the efficiency of military forces and operations. Horses throw shoes, jeeps break down, helicopter blades crack. In turn, even minor failures can have a snowball effect; for want of a horseshoe, a wagon full of gunpowder does not reach a battery short of ammunition; for want of a helicopter blade, an antiaircraft radar is not placed in a forward position.
The "fog of war" refers to the uncertainty that envelops all military operations, and the unreliability of information. The fog of war applies most obviously to uncertainty and unreliable information about the enemy. A literal fog may envelop the battlefield, concealing the enemy either from mounted cavalry scouts or from reconnaissance aircraft. The fog may be figurative; an enemy destroyer sighted briefly in
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