COMBINED ARMS. If we define the strategical unit as the smallest body composed perma nently of two or more arms. and capable of a•t -Mg independently, then the division of the Euro pean armies (the army corps of the United States Army) must he regarded as that unit. The smallest unit in which any two of the arms are combined is the cavalry brigade. which often has a horse-artillery battery attached to it, hut this is only done to make it temporarily inde pendent, and is not the rule. Ordinarily the brigade (cavalry or infantry) is the largest un mixed unit. The cavalry division is composed essentially of 2 brigades and 2 or 3 horse-bat teries, although in the United States it has 3 brigades and a battalion of horse-artillery. The infantry division (the smallest unit in which the three arms are combined 1 consists in general of 2 infantry brigades, 1 cavalry regiment, 1 field-artillery regiment. and other special troops differing in the different countries. In France, however. there is no cavalry attached to the in fantry division, and in the United States there are 3 brigades, 4 batteries, and no cavalry.
The highest definite unit of organization is the army corps, and its strength is determined by the fact that in its most unfavorable formation it must he capable of being assembled or any por tion of itself in a single day. It is composed normally of 2 infantry divisions, 1 regiment of field-artillery, train and other services. In France, as there is no cavalry with the infantry divisions, a brigade of cavalry is attached to the army corps, and in the United States this unit i; composed of three divisions, one or more regi ments of cavalry, and the corps artillery. Since the artillery reserve was given up by Germany in 1399 the principal nations have followed this example, although a few still retain it. The total
strength of an army corps is about 30,000 in all armies, forming a column about 15 miles long, its rear, therefore, one day's march from its head. Armies are simply aggregations of army corps and cavalry divisions. the artillery reserve being practically a thing of the past. The proportion of the three arms of the line is now considered to be best when the infantry and cavalry are in the ratio of 12 to 1, and there are 4 guns to every 1000 men of the other arms. The propor tion of cavalry has been gradually made smaller since the days of Frederick, while that of the artillery has been gradually increased. In diffi cult mountainous country the cavalry is usually made less, but not if it can be used in raids at a distance. The proportion of artillery in flat, heavily wooded country, or in difficult Moun tainous country, or in country where the roads are bad, is usually decreased, because the full proportion cannot he used advantageously, and a smaller proportion would diminish the length of the column, which is always desirable.
Thus far only the line of the army, in its most restricted sense, has been considered, but the efficient working of an anny also requires a number of special troops, such as the engi neers, pioneers, railroad engineers, pontoniers, sappers and miners, stpialers, telegraphers, bal loonists, and the medical corps. In foreign armies all the special troops, excepting the medi cal corps, are designated by the general term technical troops. Of course, these do not all exist in any one army. and, although the corre sponding classes in the different armies have similar duties, there is still considerable differ ence.