afford.

When the width of extension becomes very great it will be an absolute
mistake to keep back reserves, since by doing so the actual front is
weakened, whilst there is no guarantee that the reserve can arrive in
time at the threatened point.

Further, the wider the front becomes, the greater the difficulty of
strategical change of direction.

A similar extension of front as that above indicated in this resume of
'Security' duties may also become advisable when engaged on
'Reconnaissance'--for instance, when lengthy obstacles, such as
watercourses, mountains, etc., only traversable at bridges, dams, or
defiles, have to be surmounted.

In such cases, especially when resistance is to be anticipated, it
will rarely be possible to count on being able to surmount the
obstacle in one single column, since even unimportant forces under
such circumstances can oppose a very protracted defence, and
neutralize a large numerical superiority. When these difficulties are
met with, it will be necessary even in reconnaissance to divide one's
force into several columns, as then there is always the chance of
successfully piercing the enemy's front at some one point, and thence
rolling up his resistance all along the line.

Even in open country conditions may be encountered that render the
subdivision of one's forces over a considerable extent of front
desirable--_i.e._, when it is necessary to find the enemy, and fix the
fact of his presence in certain specific districts. As an example,
the conduct of the Cavalry after the Battle of Gravelotte (August 18,
1870), when it became imperative to ascertain whether MacMahon's Army
was marching to the north-eastward or not.

Here it was indispensable to sweep out a wide area. To attempt such
tasks with patrols alone is unadvisable, for these always require a
certain tactical support behind them, by which they can be either
reinforced or relieved.

Still, the point must never be lost sight of, that, since the enemy
will also seek to screen his operations, a decisive collision may
become necessary at any moment to tear his screen asunder. Hence it
will be better, in opposition to the principles laid down for
'security' only, to keep one's principal force in groups or masses,
possessing considerable striking force, and to march in such manner
that a certain degree of concentration is always attainable while
meeting the necessity for extension in breadth by smaller
reconnoitring patrol