Military power, whether afloat or ashore, has in all ages been measured in units of skilled fighting men, properly equipped. Improved equipment increased the value of the unit, as is instanced by the success of the armored Greek, when opposed to the unarmored Asiatic.
Equipment was more or less permanent, could be captured, or passed on to new men; the men were but mortal; and, on the average, lack of men set limits to the power of the state.
From this fact arose the effort to increase, by constant improvement, in the equipment, the effectiveness of the fighting man at the front, and, as civilization developed, and the mechanical arts with it, the value of the unit of power was constantly augmented.
Equipment grew in effectiveness, and also in cost. In the Middle Ages equipment became so expensive that only a small part of the fighting men could be fitted out with the best equipment. Cost is a question of labor used in production, and a certain part of the man-power is required to furnish this labor.