of withdrawal
and ability to bring the enemy under fire at long range.

655. In large commands artillery and cavalry form a very important
part of the rear guard.

_Flank Guards._

656. A _flank guard_ is a detachment detailed to cover the flank of a
column marching past, or across the front of, an enemy. It may be
placed in position to protect the passage, or it may be so marched as
to cover the passage.

657. The object of the flank guard is to hold the enemy in check long
enough to enable the main body to pass, or, like the advance guard, to
enable the main body to deploy.

Like all other detachments, it should be no larger than is necessary,
and should not be detailed except when its protection is required.

658. When a flank guard consists of a regiment or less, its distance
from the main body should not exceed a mile and a half. Practicable
communication must exist between it and the main body.

659. The flank guard is marched as a separate command; that is, with
advance or rear guards or both, as circumstances demand, and with
patrolling on the exposed flank.

660. At times it may be necessary for an advance-guard commander to
send out large reconnoitering parties which temporarily assume the
character and duties of a flank guard. Such parties should be given
specific orders as to when and where they are to rejoin the column.

CAMPS.

_SANITATION._

661. If the area of the available ground is sufficient and suitable,
the camp of the battalion or regiment should conform to the plates
published in the Field Service Regulations. Under similar favorable
conditions, the brigade may camp in column or in line of columns. In
the latter formation the interval between regiments should be about 50
yards. When the camp site has a restricted area, intervals and
distances are reduced.

Under service conditions, camp sites that will permit the encampment
of regiments and brigades as above indicated will not often be
available and regularity must be sacrificed.

662. In large commands the halt order should assign camp sites to the
next smaller commands, and the commanders of the latter should locate
their respective commands to the best advantage on the area assigned
them.

_The Selection of Camp Sites._

663. In campaign, tactical necessity may leave little choice in the
selection of camp sites, but under any conditions the requirements of
sanitation should be given every consideration consisten