There were tow basic classes of field fortifications: isolated
(also called detached) field works that were complete in and of themselves
and capable of an independent defense and lines, which were either continuous
stretches of parapet covering an extended area or groupings of isolated works
placed in defense relation to each other. Isolated field works were denominated
and often divided into sub-classes according to properties exhibited by their
traces or general outlines on the grounds. Field works that were not completely
enclosed on all sides by a continuous line of parapet were called Open
field works; those that were enclosed on all sides by a continuous parapet
were called Enclosed or Closed field works. These sub-classes were
further divided into various types of field fortifications according to the
specific arrangement of elements of their outlines. Each of these basic types
could be modified by the defensive necessities inherent to their sites in
an infinite number of ways so that two works of the same type might take
on very dissimilar appearances, but still use the same basic elements arranged
in very similar manners.
Open field works were generally used in situations where it was
desirable for the defense to see into the interior of a work or when the
rear of a fortified position was secure from attack. There were seven basic
types of open field works: Redans, Lunettes, Priest Caps,
Swallow's Tails, Tenaille Heads, Hornworks, and
Crownworks. Redans had two faces joining in a salient angle and were
generally used as the advanced works in lines with intervals and to cover
outposts in front of an army's position. Lunettes had two faces joining to
form a salient angle and two flanks extending from the faces. These were
generally used as advanced works when it was desirable to add depth to the
area covered by defensive fire.
Priest Caps had two salients with a central re-entering angle
and were generally used when it was necessary to cross columns of fire over
ground immediately in front of the work or as part of continuous lines to
provide flanking fire across sections of the line to the work's right and
left. Swallow's Tails had two salients with their capitals directed along
eccentric lines from the center of the gorge and two exterior faces directed
along lines that would intersect well to the rear of the work. These were
used in in situations where it was necessary to both cross columns of fire
immediately in front of the work and project columns of fire at angles to
the rear.
Tenaille Head, hornworks, and crownworks were more extensive than
the previous four types of open works and were generally used to fortify
bridgeheads when the flanks could be anchored on impassable watercourses.
Tenaille Heads were composed of relatively short stretches of continuous
parapet joined to form a series of alternating salient and re-entering angles.
Hornworks presented a single front of fortification on their engaged sides
which was terminated in two demi-bastions with their exterior flanks extending
rearward in directions more or less perpendicular to the front. Crownworks
included at least two fronts of fortification and a fully developed central
bastion.
Closed field works were used when it was necessary to provide
a garrison the means necessary for resisting attacks from any direction.
Closed works were used as shelter for isolated garrisons along an army's
lines of communication or as the retired works in lines with intervals. They
were also used as points of resistance within continuous lines of works.
There were three basic types of closed works: redoubts, star
forts, and field forts. Redoubts were small works that did not
include any re-entering angles. They could be circular, square, or traced
on almost any regular or irregular polygonal shape. Without re-enterings,
the ditch could not be defending by flanking fire from within the work and
had to depend either on special arrangements such as counterscarp galleries
and caponnieres or fire from other nearby works to defend the ditch. Star
forts, also called tenaille forts, were enclosed by a series of alternating
salient and re-entering angles. A star fort's salients were defended by oblique
fire from collateral faces, but the ditch was not well flanked and fire from
the parapet could not reach into the ditch at the re-entering angles.
A field fort was defined as any closed work that included re-entering
angles in its trace. Field forts could generally defend their own ditches
and project crossing columns of fire over ground immediately to their fronts,
but they also tended to be quite large and required more time and labor to
construct than most other types of works. |
