al 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.

434. 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.

435. 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.

436. 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.

A small force in a covering or delaying action requires very little
strength in rear, while a large force fighting a decisive battle
requires much. Therefore, depending upon circumstances, the original
deployment, including the strength in rear, may vary from 1 to 10 men
per yard. Against an enemy poorly disciplined and trained, or lacking
in morale, a thinner deployment is permissible.

437. The density of the whole deployment increases with the size of
the command, because the larger the command the greater the necessity
for reserves. Thus, a battalion acting alone may attack with two men
per yard of front, but a regiment, with three battalions, may only
double the front of the one battalion.

438. By the assignment of divisions or larger units to parts of a line
of battle several miles long, a series of semi-independent battle, or
local combat, districts are created.

The general deployment for a long line of battle comprising several
battle districts is not directly considered in these regulations. The
deployments treated of herein are those of the infantry within such
districts.

The density of deployment in these districts may vary greatly,
depending upon the activity expecte