D. H. (Dennis Hart) Mahan.

Summary of the course of permanent fortification and of the attack and defence of permanent works, for the use of the cadets of the U.S. Military Academy online

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Online LibraryD. H. (Dennis Hart) MahanSummary of the course of permanent fortification and of the attack and defence of permanent works, for the use of the cadets of the U.S. Military Academy → online text (page 12 of 29)
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sieged to defend the coverediway, they are palisaded, and
barriers arc placed at the defiles. As the means of protracting
tin- defence arc only effective when the defiles .-ire perfectly
secured from the tire of the enemy, established along the Crest
of the salient place of arms, the reason for the particular con*
•traction given for each traverse will now be apparent. Hie
interior crests of Nos. 1. 9 and 3 are so arranged that they
can concentrate their fire on the salient place of arms ; and
each traverse i.- so combined with the demilune, as effectually
to mask the defile of the one in rear of it. The defile of No.
1 is masked by No. -. and a passage of about 2.<» yards at
the foot of the h;ui<jiiette-slo]>e < ► t " No. 1 is covered, so that the

troop.- can pass through this defile in perfect safety.

41 5. ..The defile No. 2 is less easily covered by No. 3. To
effect it. the inner angle ot the crotchets has to be cut off and
the banquette-elope suppressed, substituting in its place Btepe;
by these means, a passage of l.o yard is •covered, and N". ■'>

placed not too far from No, -.

416... As it is hot practicable to cover the defile of No. 8, the

tion of No. i 18 determined. BO a- to make the salient
place of arms a- spacious CM possible. This is done by phi

4 in a position, to allow its exterior slope to be swept by
the fire of the bastion face, penetrating between the salient of
the demilune and the angle of the redoubt of the reentering
place of arms.

41 7. ..The defile of the traverse on the bastion covered-way,
nt any line of fire penetrating through it
Into the reentering place of arm?.

418.. .The precautions which arc here taken would 1"
insufficient, could the enemy, in possession of tin f the

salient place of arm-. ha\ e a plui red-

•rmy behind the trav< I- - to prevent tin's that th<

13H Nol/.i •■["- KKTHOD.

terior crests of the different traverses and their respective
crotchets are held in the same plane J which is bo arranged
thai the terreplein shall be defiled from the enemy's lodgment

on the crest of the salient phu f arms. Tin's arrangement

necessarily places the terreplein between the traverses on dif-
ferent level.-; small ramps will, therefore, be necess.arv to ;
from one, level t«> the other. They are placed at the defiles.

41 '.♦. ..The salient ]>laee of arms is inclined for the purpose of
partially defiling it from the trench cavalier.

420.. .Finally, tic traverses are sustained on the Bide of the
counterscarp by I profile wall, which is the prolongation of
the counterscarp wall; and they are terminated at the other
extremity by a wall, so as to make the defile convenient a> a

421. ..Coi'ntikx u;rs i>i- Tin; Bastion am> Demilcxtb. Hav-
ing determined the relief of the covered-way crests, which, it

may lie observed, is such that, they mask all the masonry Of
the scarps, and, at the same time, are BO low that an ciicmy

cammt. by the ordinary methods in use, obtain a plunging tire

from them dpOU the terrc|>lcins of the works in their rear, the

position of the counterscarp carestB can now he fixed.

I •_'•_'. ..The top of the counterscarp wall should he at least 8'
h-ct below the planes of the interior creal of the covered-way,

and the height of the wall for the body of the place should not
exceed 24 feet, and for the demilune it may be reduced to 18

feet. Tin .-e dimensions will, therefore, be assumed, as the
greatest that can he allowed with a proper regard to economy.
And a continuous wall of these heights may be regarded a- a

powerful auxiliary obstacle, in securing the works from all
attempts at surprise.

■12:;. ..Adopting the limit of 24 feet for the counterscarp of
the bastion, it will be seen that the bottom of the ditch at the

toot of this wall is higher than at the foot of the scarp wall of
the bastion face; and, as the bottom of the ditch, at the ex-
tremity of the double caponniere, has already been determined,

noizkt's method. 137

these different levels must be, connected by planes, combined*
in the most simple manner,

•|-_' !...< i M li I - LND BOTTOMS OF THE DrTOHES. PI.-. 4 Mini .'..

A dinette, 4.<> yards wide at top, and 3 feet deep, is' made in
the main ditch to serve as a drain. A cvJUoert, or small arch
of masonry, is made under the double caponniere, connecting
the cunette on the opposing .-ides of it. The cunette ifl placed
parallel to the bastion face; tin- bottom of the ditch having a
slope of 1.50 feci from the foot of the scarp wall to the edge of
the cunette, and a slope from the opposite edge up to the foot,
of the counterscarp wall. These details will he hest under-
stood by referring to I *].->. 4. 5, Figs. 1. The slopes hefre given
-erve to keep the bottom of the ditch dry; they a— i-t in ren-
dering the breach, made in the bastion face-, rather Btei
than if the bottom were horizontal : and, in the passage of the
ditch, the enemy's work i- thus more exposed than if the bot-
tom were not sloped from the foot of the counterscarp wall to

the cunette.

The demilune ditch is arranged upon similar principles. A

cunette and culvert are placed in it., to convey the rainwater
froyi it into the main ditch.

4_'.V..I'l.\\i - OF THE G The glacis of the covered-way

may now he considered. < hie principle is chiefly to be attended
to in disposing the different planes of the glacis. They should
all he swept by the artillery tire of the works immediately in
their rear, and by the niu.-k« try lire, at least, of the bastion

-iL'''>...The glacis of the bastion coverecUway should lie swept,
by the artillery of the bastion fa<

1-7. .The glacie of the re< ntering place of anas should he
swept by the tire from it- redoubt.

4l"v I j the demilune "tier,- more difficulty in its

arrange ment, owing to the cremaillece form of the interior

l>e-t method seems the following : plat
passed t as to 1

artiUerj demilun< .


13S Noi/.i r'a mi thod.

are connected by another Beries of planes, which are pas
through the salient point <»t" cadi crotchet below the plane of
musketry fire, of at Least one-half of the bastion tare; and
below thai <>f artillery fire, jrf a part of the demilune tare.

4 :.".'... It will he readily seen, from the nature of this prob-
lem, that it admits of many solutions. In selecting amoi
them, the following considerations may serve a.- guides. Wlien
the planes of the glacis have a very gentle slope, they are bet-
ter seen by the works in their rear; but the construction is
more expensive, on account of the greater quantity of em-

430... When the slope is more steep, the enemy's works on
the glacifl are better exposed to the reverse views of the collat-
eral works, although not so well seen by those directly in rear
of the glacis; but the quantity of embankment is smaller.

431...0tTLi;rs, ok Soktii: Passages. To communicate from
the covered-way with the glacis, an <>utht or 80fii< poesOffi is
cut in the least exposed face of the reentering place of arms;
and one, also, on the long branch, between the 3d and 4th
traverses. They are from 8.30 to 4.0 yards wide. The cut is
about 6 feet in depth, the earth being sustained on each side
by a protile wall. The bottom of it is a ramp leading from
the terrepleiu of the c. Aercd-way to the top of the glacis. A-
the outlet is closed by a barrier, it should be arranged at the
bottom, to alloW tin- barrier free play in opening ami shutting,

432...CoMMr.Mi'ATi"\>. There is no part of a fortification
where more care and judgment are required than in the dis-
positions made to communicate from tin- interior with the out-
works. The safety of the besieged essentially depends on a
proper disposition of the communications, which should afford
vwvy facility for offensive movements, and, at the same time,
a Beeute and easy means ot retreat. This subject has been
treated with peculiar care by Noi/.et.

b'l.'b.. Besides the ramps, which have already been explained,
DOSteraB and stairs form a part of the system of communica-

noizkt's method. 139

434.. .Posterns, as already lias been stated, arc arched com*
mnnicatione of masonry, made under the rampart or terreplein.
When these communications are required for the passage of
artillery, they Bhould be at least lo feet wide, and 8 feet high
under///- crown ot hey of tfu arch. When for infantry, they
may be reduced to 1 feet in width, and 6 feet in height, under
the key. The arch of the postern is generally a semi-circle,
<>r what is called a full centre arcA. i& be bomb-proof , it
should be at least 3 feet thick through the masonry of the arch,
«ind be covered by at least from 8 to £.60 feet of earth.

135. ..Stairs are only used in situations where ramps cannot
be placed : as for example, to communicate with the interior
of works, the gorges of which are revetted.

Cacti step is generally formed of a single block of stone,
which is 2.0 yards long m to* dear\Q.Z0 yard in width, and
0.20 yard high. Prom these dimensions of the height, or i
and width, or tread, of each step, we obtain the following for-
mula for the hase of & flight of steps ', when the height between
the two landings is idven, 8-2 // — <». 30 = 1) ase.

Stairs are not so convenient as ramps J and they are, more-
over, liable to be easily put out of order by the effects of shot
and shells.

}.',o...( , .mmi'nk \!io\ OF Tin EnCT in i i" ■ wi 'in THE iMou. —

The postern of the enceinte lead.- through the middle of the
curtain, descending from the plane of sight to the ditch. The
inclination of the bottom should never exceed 1-6. The bot-
tom should not corns out upon I Level with the bottom of the
ditch, l>ut about 6 feet above it — a wooden ramp being need to
end from the postern to the bottom of the ditch,

The width of thifl postern should be 1_ feet, both bn account
oft ter circulation through it, and because it may he

; as a bomb-proof shelter for the troops on duty.

I to this postern, both toward the ditch and the

interior, is by door-ways ; one through the scarp wall, which
closes the postern toward the ditch, and one through a
tical wall ol ty of the enceinte b

140 noizet's method.

plein, which closes the month of the postern toward the inte-
rior. The earth of the rampart-slope is cut away, to leave the
passage t" the postern free. The sides of the cut are sustained
by wing walls, which make a small angle with the vertical Wall
of the postern mouth. The door-way may be 7.0 feet wide,
ami 7.50 feel high. The postern itself being 1" feet under the

For more security, a partition wall, with a «1 '-way, is some-
times made across the postern, about the middle point. The
leaves of the folding-doors here have loop-holes to fire upon an
enemy, should he, by asurprise, gain possession of the exterior

437...Co\|Ml NI.'ATIo.N Willi 1 I! I : Tl N A I I.I.K. A postern, for

the passage of artillery, is made under the teuaille, and leads
to the double caponniere. Two stairs are placed at the gorge
of the tenaille, to communicate with its berreplein.

438...G'MMr.\i< ation with nii: Ti i;i;i and Diivii Qg

Tin; Demilune RwJoubt, Two stairs are placed at tlie^orge

of the demilune redoubt, to communicate with it* terrcplein.
A postern for artillery leads from the main ditch to the ditch
of the redoubt, under it8 flank, for the communication between
the main ditch and the demilune.
439...Co.M.Mi mi \ii<>\ 1K0M mi; Enceinte Ditch with nut

ExTEBIOB. To communicate with the covered-ways, a ramp of
earth sustained by walls i> placed along the wall that termi-
nates the demilune and its redoubt. This ramp is separated
from the extremity of the face-cover by a cut 4.30 yards wide.
•1 !<»...( 'ommimca iio.n wnii mi: DEMILUNE Gut. The com-
munication with the work behind the demilune cut is by a
postern and Stairs for infantry, which lead from a point on the

ramp just described to the terreplein of the work — passing in

a winding direction under the tcrreplcin and parapet of the

441...Commi mi ai ions of the Redoubt 01 the Ki:-i mi kim.
Place of Asms, etc The passage behind the single capon-
niere. in the demilune ditch, has already been described. The


passage leads to a postern for artillery, made through the face
of the redoubt, to its ditch. From the ditch, a ramp for ar-
tillery Ira. Is to the terreplein of the reentering place of arms.
At the angle of the redoubt on the demilune ditch, stairs are
placed to ascend to its ditch; a ramp for infantry leads from
the ditch on this side to the terreplein.

44l'...To ascend to the terreplein of the redoubt, a small

bern for infantry is made through the face to the ditch.

being placed alongside the postern just described ; from this,

a winding postern and stairs lead to the terreplein of the re-


Hie foregoing, with what has been said respecting the ca-
ponnieresj traverse defiles, etc., completes the description of
the communications of the front. This subject may l.e closed
with a recapitulation of the principal conditions wlu'ch should
regulate every system of communications.

44.".... Ki m.\i;k> om im. Communications. 1st. Tfn commu-
nication* should ?" n their position^ compromise tJu
safety ofthi < run ink .

frequent i i i.-l a l ic< 's ceul d he cited of works which have been
surprised by an enemy obtaining possession of the gates.
Therefore! too many precautions cannot be taken to secure the
principal outlet from the body of the place from similar at-
tempt.-. It is on this account that the postern in the body of
the place is arranged as has been described, to frustrate any
indden attack that might be made upon it.

i l b..L'd. 77/. communications should admit of a oonv* nu tU

ibserve this purpose, the dim* •<•.. of the

posterns, ramps, and other similar works, should be convenient

for I • which they are app I they should be

placed in such j directly to the poii

arrived at In « namii " >rra, dim :ion

the front, it will be found that th
ditions s

4 15.. .3d. 7 /<< positi

142 noket's method.

why that when cm enetny gets possession of it. In may ob-
tain ik' advantagt by it.

To be useless to an enemy, the communication, when in his
poggi ssion, should nol ofFer a shelter for his works; nor enable
liini to carry them on with more ease. Tins end will be ob-
tained by placing the communications in a position to be en-
filaded by the fire of the works in their rear; and so arranging
them as to preserve the counterscarp wall unbroken, by which
means any facility for attempts at surprise will be avoided.

4th. The communications should bt covered from every point
when an enemy might establish himself, during th< whole
peribd thai they oun h of service to tin besiegers; and they
should be swept by th> firs of thi < n<-< info .

Without these precautions, an enemy might cnt oil' all com-
munication from the enceinte with the outworks; and in cases
of retreat, the troops could not derive any assistance from the
enceinte, if he attempted to press upon them.

446.. .In covering the communications, existing masses should,
when convenient, be used, which form a part of the general
arrangement of the works. Examples of this are shown in the
manner in which the debouohS from the double caponniere,
and also those from the traverse defilesj are covered. In the
firsl case, by the angle of the counterscarp wall and the salient
of the bastion'; and in the second, by the angle of the profile
walls of the traverses and the demilune salient. Sometimes a
special mask has to be raised, an example of which is seen in
the traverse at the gorge of the red6ubt of the reentering place
ofarra8, which covers the door of the postern of the redoubt.

•1 I7..."'th. The communications should fo so placed as hot to
compromise tlu retreat of th troops.

This is effected by placing the communication in the ree*n-

terlngS, Which are the most secure points, a> an enemy to

arrive at them will have to brave a powerful column of flank
lire. Barriers, gates, and movable bridges of timber should
be placed at Buitable points, to cut off one communication

NOI/.I t's method. 143

from another; ami thus arrest the progress of a pursuing

448...6th. Finally, each work should <« independent qf every
cotflmunicatioti, except thi <>n' destined for Us particular use.

This is ;m important object, as it prevents an enemy, should
lie succeed in gaining possession of a communication leading
through it. from seizing upon tlie work itself. Examples of
this arrangement arc shown in the postern, through the face
of the redoubt of the reentering place of arms, which leads i"
the exterior, and which is not connected with the small postern
destined for the service of the redoubt itself; also, in the
postern leading from the main ditch to that of the demilune
redoubt, for the service of the demilune. This postern does

not interfere with the safety of the redoubt.

-M'.'...r.\ examining the communications of the front, gen-
erally, according to these conditions, it will he found that their
arrangement i:- a.- judicious a- the nature of the problem
seems to admit.

■l.'.n... In -,, ,;,,,,; Ri 11:1 n< iimi vis. The front, as it has now
been described, appears to be of a character to protract the
■ to the longest duration. When, however, a breach is
made in the enceinte, although military usage and a point of
honor require of the garrison to sustain, at least, one assault,
the consequences of defeat are of too serious a character to ex-
• such an effort, unless a place of safety i> provided, into
which the garrison may retreat, after defending the breach,
and obtain an honorable capitulation. <h\ this account, and
to lengthen the defence, interior retrenchments tax made
in the bastions. These works may he either of a temporary or
permanent character; hut i; led that the

latter class alone off tele to t :

former, mor» ! it the bi ould be full,

that the retrenchment Bhottld be thrown up during
an nndertaki lifficulty, both from tl

the enemy's lire and tie I
ordinary dut


451. ..Therefore, only the permanent interior retrenchments
with a revetted Bcarp and counterscarp will be given : and
which may be regarded as an element of a regularly fortified


•1 .",_'.. .Xoizet, like Cormontaingne, proposesfour classes of in-
terior retrenchments. 1st. Those thai rest against the faces of
the bastions. 2d. Those that rest against the flanks. 3d.
Those that rest against two adjacent curtains. 4th. Those that
comprehend several bastions.

•!."•:'.. ..Fiust CLA88 RESTING ON Till: FACES. PI. G, Fig8. 1. -,

and .1. />. Fig. 3. The first class may be either the form of a

cavalier, shut in by cuts across the bastion faces, or an inverted
redan ; or, finally, if the bastion is very open, a small bastion
front. Of this class, the cavalier has been generally employed.
The cavalier receiving a relief so great as to give it a plunging
fire upon the enemy's works on the glacis of the bastidned cov-
ered-way ; whilst the interior of the bastion, in advance of the
cavalier ditch and of the cuts or ditches across the bastion tcr-
replein, between the scarps of the bastion and cavalier, is
swept, and the breach that might be made in the bastion
salient can be defended from the parapets behind the cuts.
These parapets, with the portions of the cavalier faces in ad-
vance of them-, forming the interior retrenchment.

1. vi. ..This class presents the advantages of defending the
breach within a short distance, and by enclosing the thinks of
tli.' bastion within them, they preserve the thinking arrange-
ments of the body of the place until the retrenchment is car-
ried. The principal objection to them is that, by a breach
made at lite shotllder angle, the enemy can turn them.

45 5... Second class besting AjGAINST the Planes. PI. 6, Figs.
4 and C. The second class may be of an inverted redan, or a
small bastion front; or, finally, of a redan resting against the
middle of the flanks, its faces having such a direction that its
ditch maybe swept by the fire of the flanks of the adjacent

l>a.-tions. .
The last form admits of defending the breach within a short

noi/.kt's METHOD. 145

distance; it preserves also the flanking arrangements of the
enceinte, and can only be turned by a breach made id the cur-
tain. To sweep its ditch from the opposite Hank, it will be
neog&sary to cut down a pari of the scarp wall of the flank on
which the ditch rests^ which will make the height of the wall
less than 11.0 yard.-, and somewhat expose the enceinte to

1 .■"><!. ..Tmiti> ei.\ - BESTEN& ON 5PW0 aim \< r.\ i ( 'i i;i wins. PI.
6, Fig. 4. I>. The third class is usually of the form of a has-
tened front ; but as the tire of its-faces would be masked by
the curtain of the enceinte, it is generally beet to construct the
front simply with a curtain and two flanks.

Thi.- class being thrown farther from the salient of the bas-
tion, does not defend the breach so directly as the two preced-
ing; but its position i> stronger, and will force an enemy to
employ more means t<- carry it. From its djmensions, it will
require more space on the interior, and will he also more ex-
pensive than either of the preceding tonus.

4r»7...Foi inn <i.\— i mi.o-im, >;.\i. Fbohts. The fourth
clas-, which is placed in the rear of .-evoral hastions of the en-
ceinte, or properly, several fronts, [e a kind of sec. . ml enceinte

within tiie ftrat. An arrangement of this character would, of
course, require a peculiar locality, and would seldom find an
458... < \ •> •. i .ii i; wiiu Oon i.\ mi Bjjstios F.\< i -. I'l. 6,
s. 1, 2. The - work are parallel to those of the

bastion in which it is placed ; its ditch should be about L8 feet
>w the bastion terreplein : it.- scarp wall about l'4 feet high.
And it may be I d that ali interior retrenchnu

to ope - oa obstacle to an enemy, should bav<

ments of about these dimensii

'4.'. '.'...The interior crest of I bould be so high that the

line of fire, from the salient of the cavalier to the salient of the

bs^tion rn\, red-way, shall pas.- above the bastion salient. I'.v

the counterscarp ol the cavalier at L4.0 yards from the

interior crest of the bi allowing L1.0 vard- for the width


146 Noi/.l !*- Mi THOD.

of tin- ditch, and making the bottom of the ditch 18 feet In-low
the bastion terreplein— it will be found that the reference fitf
the bottom of the ditch will be (58.50); the scarp wall being
et high, the reference of its magistral be (82.50). Now,
if the reference of the interior crest be taken at (97.50), or 15
feel above the magistral, its projection will be at 33.16 feet, or
11.Q6 yard.- from the magistral : and as both the lines arc hor-
izontal, parallel to it. Drawing, then, three lines parallel to
the bastion interior crest, at the distance above mentioned, the
projections of the counterscarp, scarp and interior crest of the
cavalier are obtained. The position here given to the interior
crest of the face will satisfy the condition first laid down.

40<>. ..The interior crest of the think Is also horizontal-; its
reference, therefore, is ( ( .i7."> ,, i ; the direction of the Hank 14
perpendicular to the line of defence of the bastion ; the think,
moreover, is not. revetted like the face, but is terminated by
prolonging its exterior slope to thenastion terreplein ; the low-
est point of the foot of this exterior slope will, therefore, he

about (T-':. (,i M, the reference of the hastioii terreplein at the ex-
tremity of its flank; the least width of the bastion terreplein,
between ItB think and that of the cavalier, should be 14.0 yards.
If, then, from the interior angle Of the curtain, with a radius of
14.0 yards, atn arc be desoribed, and a tangent be drawn to this
arc, perpendicular to the line of defence, this tangent may he
taken as the horizontal of the exterior slope of the cavalier
flank, whose reference is (73.0) ; the interior crest of the flank
is drawn parallel to this horizontal, and at 41.10 feet, or L8/f$
vanU from it ; which will be the distance found by calculation,
the thickness of the parapet being 20 feet, the superior slope
I-*;, and the exterior .-lope 1-1.

-lol...The lengtb of the flank is found by drawing, through

Online LibraryD. H. (Dennis Hart) MahanSummary of the course of permanent fortification and of the attack and defence of permanent works, for the use of the cadets of the U.S. Military Academy → online text (page 12 of 29)