One of the most obvious and advantageous departures from the so-called laws of war is the action of scattered groups against men pressed together in a mass. Such action always occurs in wars that take on a national character. In such actions, instead of two crowds opposing each other, the men disperse, attack singly, run away when attacked by stronger forces, but again attack when opportunity offers. This was done by the guerrillas in Spain, by the mountain tribes in the Caucasus, and by the Russians in 1812.

People have called this kind of war "guerrilla warfare" and assume that by so calling it they have explained its meaning. But such a war does not fit in under any rule and is directly opposed to a well-known rule of tactics which is accepted as infallible. That rule says that an attacker should concentrate his forces in order to be stronger than his opponent at the moment of conflict.

Guerrilla war (always successful, as history shows) directly infringes that rule.

This contradiction arises from the fact that military science assumes the strength of an army to be identical with its numbers. Military science says that the more troops the greater the strength. Les gros bataillons ont toujours raison. *
* Large battalions are always victorious.

For military science to say this is like defining momentum in mechanics by reference to the mass only: stating that momenta are equal or unequal to each other simply because the masses involved are equal or unequal.

Momentum (quantity of motion) is the product of mass and velocity.
In military affairs the strength of an army is the product of its mass and some unknown x.

Military science, seeing in history innumerable instances of the fact that the size of any army does not coincide with its strength and that small detachments defeat larger ones, obscurely admits the existence of this unknown factor and tries to discover it—now in a geometric formation, now in the equipment employed, now, and most usually, in the genius of the commanders. But the assignment of these various meanings to the factor does not yield results which accord with the historic facts.

Yet it is only necessary to abandon the false view (adopted to gratify the "heroes") of the efficacy of the directions issued in wartime by commanders, in order to find this unknown quantity.

That unknown quantity is the spirit of the army, that is to say, the greater or lesser readiness to fight and face danger felt by all the men composing an army, quite independently of whether they are, or are not, fighting under the command of a genius, in two—or three-line formation, with cudgels or with rifles that repeat thirty times a minute. Men who want to fight will always put themselves in the most advantageous conditions for fighting.

The spirit of an army is the factor which multiplied by the mass gives the resulting force. To define and express the significance of this unknown factor—the spirit of an army—is a problem for science.

This problem is only solvable if we cease arbitrarily to substitute for the unknown x itself the conditions under which that force becomes apparent—such as the commands of the general, the equipment employed, and so on—mistaking these for the real significance of the factor, and if we recognize this unknown quantity in its entirety as being the greater or lesser desire to fight and to face danger. Only then, expressing known historic facts by equations and comparing the relative significance of this factor, can we hope to define the unknown.

Ten men, battalions, or divisions, fighting fifteen men, battalions, or divisions, conquer—that is, kill or take captive—all the others, while themselves losing four, so that on the one side four and on the other fifteen were lost. Consequently the four were equal to the fifteen, and therefore 4x = 15y. Consequently x/y = 15/4. This equation does not give us the value of the unknown factor but gives us a ratio between two unknowns. And by bringing variously selected historic units (battles, campaigns, periods of war) into such equations, a series of numbers could be obtained in which certain laws should exist and might be discovered.

The tactical rule that an army should act in masses when attacking, and in smaller groups in retreat, unconsciously confirms the truth that the strength of an army depends on its spirit. To lead men forward under fire more discipline (obtainable only by movement in masses) is needed than is needed to resist attacks. But this rule which leaves out of account the spirit of the army continually proves incorrect and is in particularly striking contrast to the facts when some strong rise or fall in the spirit of the troops occurs, as in all national wars.
The French, retreating in 1812—though according to tactics they should have separated into detachments to defend themselves—congregated into a mass because the spirit of the army had so fallen that only the mass held the army together. The Russians, on the contrary, ought according to tactics to have attacked in mass, but in fact they split up into small units, because their spirit had so risen that separate individuals, without orders, dealt blows at the French without needing any compulsion to induce them to expose themselves to hardships and dangers.