enemy's movements and of giving an
accurate account of them to the general, thus enabling him to make his
plans understandingly. The commander of the advanced guard should assist
the general in the same way. A general advanced guard should be composed
of light troops of all arms, containing some of the _elite_ troops of
the army as a main body, a few dragoons prepared to fight on foot, some
horse-artillery, pontoniers, sappers, &c., with light trestles and
pontoons for passing small streams. A few good marksmen will not be out
of place. A topographical officer should accompany it, to make a sketch
of the country a mile or two on each side of the road. A body of
irregular cavalry should always be attached, to spare the regular
cavalry and to serve as scouts, because they are best suited to such
service.

5. As the army advances and removes farther from its base, it becomes
the more necessary to have a good line of operations and of depots which
may keep up the connection of the army with its base. The staff officers
will divide the depots into departments, the principal depot being
established in the town which can lodge and supply the greatest number
of men: if there is a fortress suitably situated, it should be selected
as the site of the principal depot.

The secondary depots may be separated by distances of from fifteen to
thirty miles, usually in the towns of the country. The mean distance
apart will be about twenty to twenty-five miles. This will give fifteen
depots upon a line of three hundred miles, which should be divided into
three or four brigades of depots. Each of these will have a commander
and a detachment of troops or of convalescent soldiers, who regulate the
arrangements for accommodating troops and give protection to the
authorities of the country, (if they remain;) they furnish facilities
for transmitting the mails and the necessary escorts; the commander sees
that the roads and bridges are kept in good order. If possible, there
should be a park of several carriages at each depot, certainly at the
principal one in each brigade. The command of all the depots embraced
within certain geographical limits should be intrusted to prudent and
able general officers; for the security of the communications of the
army often depends on their operations.[37] These commands may sometimes
become strategic reserves, as was explained in Art. XXIII.; a few good
battalions, with the assistance of movable detachments p