t its centre, when lying
for any length of time in camp. Only current supplies are kept on hand
at the latter, and no surplus is transported on the march, except the
required amounts of subsistence and forage.

A great deal is said in connection with military movements, of 'bases of
operation.' These are the points in the rear of an army from which it
receives supplies and reenforcements, and with which its communications
must at all hazards be kept open, except it has means of transportation
sufficient to render it independent of its depots for a considerable
period, or unless the country traversed is able to afford subsistence
for men and animals. When an army marches along a navigable river, its
secondary base becomes movable, and it is less confined to the necessity
of protecting its rear. In Virginia, however, the connection of the Army
of the Potomac with Washington is imperative, and this fact explains the
contracted sphere of the operations of that army.

The transportation of supplies is limited by the ability of the
Government to provide trains, and by the ability of the army to protect
them; for large trains create large drafts on the troops for teamsters,
pioneers, guards, etc. An army train, upon the most limited allowance
compatible with freedom of operations for a few days, away from the
depots, is an immense affair. Under the existing allowances in the Army
of the Potomac, a corps of thirty thousand infantry has about seven
hundred wagons, drawn by four thousand two hundred mules; the horses of
officers and of the artillery will bring the number of animals to be
provided for up to about seven thousand. On the march it is calculated
that each wagon will occupy about eighty feet--in bad roads much more;
consequently a train of seven hundred wagons will cover fifty-six
thousand feet of road--or over ten miles; the ambulances of a corps will
occupy about a mile, and the batteries about three miles; thirty
thousand troops need six miles to march in, if they form but one column;
the total length of the marching column of a corps is therefore _twenty
miles_, even without including the cattle herds and trains of bridge
material. Readers who have been accustomed to think that our armies have
not exhibited sufficient energy in surmounting the obstacles of bad
roads, unbridged streams, etc., will be able to estimate, upon the above
statements, the immense difficulty of moving trains and artillery. The
trains of an