We will now discuss the particular manner of arranging the troops on the line of battle, or the manner of employing each arm, without entering, however, much into the detailed tactics of formation and instruction.

We shall begin with infantry, as the most important arm on the battle-field.

There are four different ways of forming infantry for battle:  1st, as tirailleurs, or light troops; 2d, in deployed lines; 3d, in lines of battalions, ployed on the central division of each battalion, or formed in squares; 4th, in deep masses.

These different modes of formation are reduced to four separate systems:  1st, the thin formation of two deployed lines; 2d, a line of battalions in columns of attack on the centre, or in squares by battalions; 3d, a combination of these two, or the first line deployed, and the second in columns of attack; and 4th, the deep formation of heavy columns of several battalions.  The tirailleurs are merely accessories to the main forces, and are employed to fill up intervals, to protect the march of the columns, to annoy the enemy, and to manoeuvre on the flanks.

1st.  Formerly the line of battle for infantry was very generally that of two deployed lines of troops, as shown in Fig. 26.  But reason and experience have demonstrated that infantry in this thin or light order, can only move very slowly; that in attempting rapid movements it breaks and exhibits great and dangerous undulations, and would be easily pierced through by troops of a deeper order.  Hence it is that the light formation is only proper when the infantry is to make use of its fire, and to remain almost stationary.

2d.  If the formation of a line of battalions in columns of attack be employed, the depth and mobility will depend upon the organization or habitual formation of this arm.

In our service a battalion is supposed to be composed of ten companies, each formed in three ranks.  The two flank companies are designed for tirailleurs.  This would give a column of four divisions, and consequently twelve files deep; and as only two of these files could employ their fire, there would be much too large a portion of non-combatants exposed to the enemy’s artillery.  In practice, however, we employ the two-rank formation, which, if the flank companies be detached, would give a column of attack eight files in depth, which is not objectionable.  If however, the flank companies should be present in the battalion, the depth of the column would still be ten files.

In the French service, each battalion is composed of four divisions, formed in either two or three ranks.  The two-rank formation is the one habitually employed.  If all the companies be present, and the formation in three ranks, the depth of column will be twelve files; if in two ranks the depth will be eight, files.  If the flank companies be detached, the depth of column will be, for three ranks nine files, and for two ranks six files. (Figs. 27 and 28.)