knowledge of economic principles is, accordingly, of greater importance than a knowledge of technical details. It will, therefore, be of interest to consider these principles in their application to warfare.

In war the highest economy is victory, and the greatest waste is defeat; consequently, anything which contributes to victory and evades defeat is justifiable, however great its cost or the incidental waste involved—of course within the limits of reason and common sense. A free and rapid expenditure of available resources in war is not waste, but the highest form of economy when it contributes to early victory. The march of events is rapid in modern war. A few days, even a few hours, have decided the issue of battle. The Commander does not ask his Engineer, "How much will your bridge cost?" but, "How soon will it be ready?"

In civil bridge construction the essential requirements, in their usual order of importance, are: initial cost, safety, durability or permanence, time required for construction, and aesthetics. The time required for construction is of importance chiefly in so far as it affects the financial returns on the investment. A considerable time spent in design and other preliminaries to construction, and on the work itself, will usually be amply justified by a material saving in cost.

The Time Factor Substituted for the Cost Factor

In military construction some of these desiderata entirely disappear, and the order of importance of others is reversed. In particular, the time of construction becomes of paramount importance the time factor is substituted for the cost factor as the principal consideration. In sharp contrast to civil practice, we find that any cost will be justified, if it results in saving of valuable time at a critical juncture. As a consequence of this, the construction of military bridges is conducted with feverish rapidity. The highest achievement of the military bridge builder is a structure just sufficient for its immediate purpose, erected in the minimum time, without undue regard for cost, appearance, or durability. Time is always the chief—often the only—consideration; delay is always inadmissible; and success is the only criterion by which the engineer will be judged.

In civil construction time is of importance; but it is seldom necessary to sacrifice cost, safety, and all other considerations to gain time. A delay for a moderate period will usually not be hurtful. In military operations, on the contrary, a delay of a few days, or even a few hours, may mean failure instead of success. A similar situation sometimes arises in civil bridge practice, as, for example, when it is necessary to restore traffic on an important main-line railroad after a bridge has been destroyed by fire or flood. In such a situation the economics are similar to those of warfare; and military methods of procedure would there be appropriate.

The Principle of "Bare Necessities Only"

Military bridges are always required in the least possible time, and there will very often, perhaps usually, be a dearth of building material.