[445]. Number of troops to be deployed in beginning. To gain decisive results, it will generally be necessary to use all the troops at some stage of the combat. But in the beginning, while the situation is uncertain, care should be taken not to engage too large a proportion of the command. On the other hand, there is no greater error than to employ too few and to sacrifice them by driblets. (For division of the battalion in attack see [335]–339.) (431)
[446]. Dense, well-directed, and controlled line of heavy fire gives fire superiority. When it is intended to fight to a decision, fire superiority is essential. To gain this, two things are necessary: A heavy fire and a fire well-directed and controlled. Both of these are best obtained when the firing line is as dense as practicable, while leaving the men room for the free use of their rifles.
If the men are too widely separated, direction and control are very difficult, often impossible, and the intensity of fire is slight in proportion to the front occupied. (432)
[447]. Density of 1 man per yard; occupation of only sections of long lines. In an attack or stubborn defense the firing line should have a density of one man per yard of front occupied.
Where the tactical situation demands the holding of a line too long to be occupied throughout at this density, it is generally better to deploy companies or platoons at one man per yard, leaving gaps in the line between them, than to distribute the men uniformly at increased intervals. (433)
[448]. Use of thin firing line. A relatively thin firing line may be employed when merely covering the movements of other forces; when on the defensive against poor troops; when the final action to be taken has not yet been determined; and, in general, when fire superiority is not necessary. (434)
[449]. Length of firing line employed by whole force; strength of supports and reserves; density of charging line. The length of the firing line that the whole force may employ depends upon the density of the line and the strength in rear required by the situation.
Supports and reserves constitute the strength in rear.
In a decisive attack they should be at least strong enough to replace a heavy loss in the original firing line and to increase the charging line to a density of at least one and one-half men per yard and still have troops in rear for protection and for the other purposes mentioned above. (435)
[450]. Strength of reserve; troops deployed varying from 1 to 10 men per yard. In the original deployment the strength of the reserve held out by each commander comprises from one-sixth to two-thirds of his unit, depending upon the nature of the service expected of the reserve.