It is not proposed to go into historical or other details of this
branch of the subject, but to give in a condensed form some account of
siege operations. According to the text books, the first thing to be
done, if possible, in case of a regular siege, is to "invest" the
fortress. This is done by surrounding it as quickly as possible with a
continuous line of troops, who speedily intrench themselves and mount
guns bearing outward on all lines of approach to the fortress, to
prevent the enemy from sending in supplies or re-enforcements. As this
line must be at considerable distance from the fort, it is usually
quite long, and so is its name, for it is called the line of
"Circumvallation." Inside of this line is then established a similar
line facing toward the fort, to prevent sorties by the garrison. This
line is called the line of "Countervallation," and should be as close
to the fort as the range of its guns and the nature of the ground will
permit. From this line the troops rush forward at night and open the
trenches, beginning with what is called the first parallel, which
should be so laid out as to envelop those parts of the fort which are
to be made the special objects of attack. From this first parallel a
number of zigzag trenches are started toward the fort and at proper
intervals other parallels, batteries, and magazines are built; this
method of approach being continued until the besieged fort is reached,
or until such batteries can be brought to bear upon it as to breech
the walls and allow the attacking troops to make an assault.
During these operations of course many precautions must be observed,
both by the attacking and defending force, to annoy each other and to
prevent surprise, and the work is mostly carried on under cover of the
earth thrown from the trenches. These operations were supposed to
occupy, under normal conditions, about forty-one days, or rather
nights, as most of the work is done after dark, at the end of which
time the fort should be reduced to such a condition that its
commander, having exhausted all means of defense, would be justified
in considering terms of surrender.
The _Theoretical Journal_ of the siege prescribes just what is to be
done each day by both attack and defense up to the final catastrophe,
and this somewhat discouraging outlook for the defenders was forcibly
illustrated by the late Captain Derby, better known by the reading
public as "John Phoenix," who, when a cadet, was called upon by
Professor Mahan to explain how he would defend a fort, mounting a
certain number of guns and garrisoned by a certain number of men, if
besieged by an army of another assumed strength in men and guns,
replied:
"I would immediately evacuate the fort and then besiege it and capture
it again in forty-one days."
Of course the fallacy of this reasoning was in the fact that the
besieging army is generally supposed to be four or five times as large
as the garrison of the fort; the primary object of forts being to
enable a small force to hold a position, at least for a time, against
a much larger force of the enemy.
Sieges have changed with the development of engines of war, from the
rude and muscular efforts of personal prowess like that described in
Ivanhoe, where the Black Knight cuts his way through the barriers with
his battle axe, to such sieges as those at Vicksburg, Petersburg, and
Plevna, where the individual counted for very little, and the results
depended upon the combined efforts of large numbers of men and
systematic siege operations. It should also be noticed that modern
sieges are not necessarily hampered by the rules laid down in text
books, but vary from them according to circumstances.
For example, many sieges have been carried to successful issues
without completely investing or surrounding the fortress. This was the
case at Petersburg, where General Lee was entirely free to move out,
or receive supplies and re-enforcements up to the very last stages of
the siege. In other cases, as at Fort Pulaski, Sumter, and Macon, the
breeching batteries were established at very much greater distances
than ever before attempted, and the preliminary siege operations were
very much abbreviated and some of them omitted altogether. This is not
an argument against having well defined rules and principles, but it
shows that the engineer must be prepared to cut loose from old rules
and customs whenever the changed state of circumstances requires
different treatment.