reconnaissance must be made to determine the enemy's position, the
location of his flanks, the character of the terrain, the nature of
the hostile field works, etc., in order to prevent premature
deployment and the resulting fatigue and loss of time.

It will frequently be necessary to send forward a thin skirmish line
in order to induce the enemy to open fire and reveal his position.
(393)

=408. Extent of reconnaissance.= It will frequently be impossible to
obtain satisfactory information until after the action has begun. The
delay that may be warranted for the purpose of reconnaissance depends
upon the nature of the attack and the necessity for promptness. For
example, in a meeting engagement, and sometimes in a holding attack,
the reconnaissance may have to be hasty and superficial, whereas in an
attack against an enemy carefully prepared for defense there will
generally be both time and necessity for thorough reconnaissance.
(394)

=409. Reconnaissance in defense.= In defense, reconnaissance must be
kept up to determine the enemy's line of advance, to ascertain his
dispositions, to prevent his reconnaissance, etc.

Patrols or parties posted to prevent hostile reconnaissance should
relieve the main body of the necessity of betraying its position by
firing on small bodies of the enemy. (395)

=410. Duration of reconnaissance; protection of flanks.=
Reconnaissance continues throughout the action.

A firing or skirmish line can take care of its front, but its flanks
are especially vulnerable to modern firearms. The moral effect of
flanking fire is as great as the physical effect. Hence, combat
patrols to give warning or covering detachments to give security are
indispensable on exposed flanks. This is equally true in attack or
defense. (396)

=411. Responsibility of infantry commanders for reconnaissance;
surprise unpardonable.= The fact that cavalry patrols are known to be
posted in a certain direction does not relieve infantry commanders of
the responsibility for reconnaissance and security.

To be surprised by an enemy at short range is an unpardonable offense.
(397)

=412. Commander of flank battalion responsible for security of his
flank.= The commander of a battalion on a flank of a general line
invariably provides for the necessary reconnaissance and security on
that flank unless higher authority has specifically ordered it. In
any event, he sends out combat patrols as needed.

Where his battalion