Hess Earl J. Field Armies and Fortifications in the Civil War: The Eastern Campaigns, 1861-1864

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Field Armies & Fortifications

in the Civil War

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1:Engineering War

esponsibility for fortiﬁcations in the pre–Civil War

army rested with the Corps of Engineers, the elite of the

military establishment. Created initially by the Second

Continental Congress in 1779 and renewed in different

form by the Congress of the new government in 1794,

the corps was institutionalized in its current form in 1802. A separate group

of topographical engineers, responsible for mapmaking, was created in the

War of 1812 and given its own institutional status in 1838 as the Corps of

Topographical Engineers. The U.S. Engineer Department was created imme-

diately after the War of 1812 to serve the administrative needs of the corps. It

was headed by the chief engineer.

∞

The Corps of Engineers owed its status to its role as keeper of a body of

technical knowledge and its tight connection with the U.S. Military Academy

at West Point. Created in 1802, the academy had a curriculum that was

heavily oriented toward engineering. Political support for it stemmed largely

from the assumption that West Point could produce a number of well-trained

engineers who would eventually return to civilian life with their technical

skills. The Corps of Engineers controlled the academy. Only engineer ofﬁcers

were appointed as superintendents, and most of the faculty were former or

current members of the corps. Beginning in 1842, the assistant professor of

engineering was required to participate in postgraduate training in mili-

tary engineering under the academy’s most famous faculty member, Dennis

Hart Mahan, the acknowledged expert on fortiﬁcations in the United States.

Mahan put his students through a rigorous pace in this course, requiring

each one to design a fortiﬁcation for a particular site and plan an attack

against it.

Cadets also were exposed to practical experience in ﬁeld fortiﬁcation. In

his third year at the academy, Cyrus B. Comstock took a course called Practi-

cal Engineering. He and his classmates spent two hours every day making

fascines, gabions, and sap rollers. The class regularly visited Washington

Valley, where the only company of engineers in the army maintained a dem-

onstration site. Here the cadets watched as saps and parallels were made,

inspected ‘‘a small lunette with palisaded gorge,’’ or looked at the effects of

2 Engineering War

10-inch Columbiad ﬁre on ‘‘different materials for embrasures.’’ They used

sticks to proﬁle the shape of a parapet and studied examples of several

different types of obstructions, from abatis to chevaux-de-frise. Civil engi-

neering was a large component of the academy curriculum as well. The top

graduates of the academy, roughly 12 percent, were commissioned directly

into the engineers, the topographical engineers, or as ordnance ofﬁcers.

≤

The prestige of the Corps of Engineers, as well as its connection to the

academy, was the basis of its elevated status within the army, a status jeal-

ously guarded by the ofﬁcers who headed the corps. The corps liked to throw

its weight around during intramural conﬂicts, and it also was the most politi-

cally active branch of the army. Corps heads often fought with politicians

over West Point and the other major aspect of the corps’ existence, its respon-

sibility for building and maintaining an ambitious and very expensive system

of coastal forts. Approved in the wake of the army’s dismal performance in

the War of 1812, the Third System consisted of about twenty-ﬁve masonry

forts of various sizes and designs strung out along the coastline of the United

States. Costing millions of dollars and mostly complete by the time of the

Civil War, it was ‘‘the centerpiece of national defense,’’ in the words of histo-

rian William B. Skelton.

≥

The emphasis on coastal forts helped to justify the maintenance of the

Coast Survey, created in 1807 to map the long coastline of the country. It

operated under a limited budget and relied heavily on navy and army engi-

neers for survey duties. The Coast Survey also hired promising civilians and

gave them valuable topographical engineering experience. It provided an-

other pipeline, besides West Point, for the training of engineers experienced

in government-sponsored projects.

∂

As the primary repository of technical expertise in engineering, the corps

had a heavy inﬂuence on the many U.S. military missions sent to observe

European armies. American ofﬁcers traveled to Europe more than 150 times

from the end of the War of 1812 until the outbreak of the Civil War. While

more than half of those trips were undertaken as private travel by ofﬁcers on

leave, the rest were ofﬁcially ﬁnanced observer missions. The Thayer-McRee

Mission of 1815–17 was important in bringing to America the idea that all

things French were the ﬁnal word in military affairs.

But more important than the Thayer-McRee Mission was the Delaﬁeld

Commission of 1855–56. Three ofﬁcers took part: Maj. Richard Delaﬁeld of

the engineers, Maj. Alfred Mordecai of the Ordnance Department, and Capt.

George B. McClellan of the cavalry. All three had originally been commis-

sioned into the Corps of Engineers upon their graduation from West Point.

The object of the commission was to observe military operations in the

Engineering War 3

Crimean War, but the three ofﬁcers traveled all over Europe, observing the

gamut of military matters. They left on April 11, 1855, and visited England,

France, Prussia, Poland, Russia, Berlin, Vienna, and Constantinople. Diplo-

matic red tape and military suspicions on the part of the French delayed their

arrival at the theater of war until the siege of Sebastopol was over. The

Americans reached Sebastopol a month after the city fell to the combined

French and English armies on September 8, 1855. After a month of observa-

tion, they returned to Vienna and then toured Italy, the Rhine Valley, Water-

loo, Paris, and London. By the time the three ofﬁcers returned to New York

on April 28, 1856, they had traveled 20,000 miles.

∑

The Delaﬁeld Commission was unique in that it was the ﬁrst to survey sev-

eral countries and the ﬁrst to see the immediate aftermath of operations.

Each commissioner wrote a separate, lengthy report. Delaﬁeld concentrated

on engineering but did not complete his report until November 1860. Mor-

decai wrote on artillery and ordnance, while McClellan wrote on cavalry,

to a degree, but mostly ranged widely across the whole spectrum of mili-

tary matters.

The result of their labor was impressive; each man wrote with a ﬁne de-

gree of professionalism, detail, and evaluation. But none of them discerned

very well how the early signs of technological innovation were beginning to

change military operations. They noted a wide array of new developments,

ranging from the use of processed foods and submarine torpedoes to the

construction of a military railroad for the tactical support of the English

army. But they failed to ponder the effect of the widespread use of riﬂes on

tactical formations. The technological developments were eagerly described,

often in minute detail, but there was no recognition that they might begin to

challenge how armies traditionally fought.

Overall, the commissioners took away from their long tour of Europe an

awareness that the scale of warfare had changed and that the mobiliza-

tion of manpower and military resources had increased to create expanded

ﬁeld armies. But they also sensed a threat to American security from this

and argued the need for strengthening the Third System of seacoast forti-

ﬁcations.

∏

It was a rather self-serving performance, however, and much of it rein-

forced old ways of doing things in the American military, despite some minor

technical recommendations. Also, the commissioners unsuccessfully tried to

portray the French model as outdated and the Russians as the truly admi-

rable belligerent in this conﬂict. Objectively, the Russian nation and its army

were hardly suitable models for intelligent professionals of a modernizing

nation; the suggestion fell on deaf ears.

4 Engineering War

Delaﬁeld’s comments on matters relating to fortiﬁcations were interest-

ing. He focused intently on seacoast forts everywhere he went and provided

extraordinary maps, sketches, and diagrams of dozens of works in several

countries. Delaﬁeld also was impressed by the European art of protecting

ﬁxed assets on land with scientiﬁcally designed permanent fortiﬁcations. He

emphasized the success of the huge masonry forts built by the Russians to

protect the entrance to the harbor at Sebastopol in repelling an Allied naval

attack in October 1854.

But Delaﬁeld paid some attention to ﬁeld fortiﬁcations as well. Both he

and McClellan lauded the Russians for the tenacity with which they defended

a line of hastily constructed ﬁeldworks to cover the southern approaches to

Sebastopol. The Russians held out for eleven months, even though they were

heavily outnumbered in both infantry and artillery in the latter stages of the

siege. ‘‘Such was the efﬁcacy and power of temporary ﬁeld fortiﬁcations, with

inexhaustible supplies of the munitions of war,’’ commented Delaﬁeld. The

Russians were the ﬁrst to use what came to be called riﬂe pits, small holes dug

for one to twenty men forward of their defense line. Soldiers armed with

riﬂes harassed Allied work parties on a daily basis from these pits, which

were typically protected by gabions ﬁlled with stone or dirt. Delaﬁeld felt this

tactic of harassment was ‘‘unusual.’’ He also gathered a number of photo-

graphs of the Russian works at Sebastopol and included exquisite line draw-

ings based on them to illustrate his report. Few other visual documents

convey the squalor of a small fortiﬁcation that has endured months of bom-

bardment better than these remarkable illustrations.

All three reports of the Delaﬁeld Commission were widely distributed in

the army and were well respected by ofﬁcers and interested civilians alike.

But these reports had limited impact on the thinking and doctrine of the

American army. This was due in part to the onset of the Civil War soon after

the reports were published, and to the fact that there were relatively few

recommendations in the reports. Delaﬁeld’s comments on the efﬁcacy of

ﬁeld fortiﬁcations apparently had no inﬂuence on professional army ofﬁcers,

and the fact that the coming Civil War would be fought by an avalanche of

volunteers who had never read the report made it even less inﬂuential. The

signiﬁcance of the Delaﬁeld Commission lies in the fact that the American

army was obviously growing in its sense of professionalism and study. It still

had a long way to go in terms of divining new trends that might affect how

armies operated in the ﬁeld and then moving aggressively toward meeting

the challenges that change offered. McClellan sounded a plaintive note of

despair in his report, which illustrated how far the army had to go to be a

Engineering War 5

top-notch military force. He bemoaned the size of the American engineer

establishment, calling it ‘‘ridiculously and shamefully small.’’

∫

Theory and Doctrine

To the extent that the pre–Civil War army had a set of theories that could

be called a doctrine, prevailing thoughts on the role of fortiﬁcations in the

operations of ﬁeld armies centered on whether they should be used for

offensive or defensive purposes. Dennis Hart Mahan was the only inﬂuential

American theorist in this regard. A graduate of the West Point class of 1824,

Mahan studied at the French School of Application for Artillery and Engi-

neering at Metz from 1825 to 1830. He returned to West Point soon after he

came home to teach engineering, and he held the position until his death in

1871. Mahan had an extraordinary inﬂuence on the creation of professional

standards of military engineering in the United States, both through his

classes at West Point and through his book A Complete Treatise on Field

Fortiﬁcations (1836). He later wrote six more books on warfare and engineer-

ing. Mahan also was primarily responsible for establishing standards of pro-

fessionalism in civil engineering. The several reprintings of his Complete

Treatise not only informed regular ofﬁcers, but they were widely read by the

pre–Civil War militia and by volunteer ofﬁcers during the war.

Ω

Mahan revised prevailing French military thinking about the role of for-

tiﬁcations in ﬁeld operations. Theorists of Napoleon’s day had advocated

maneuver and ﬂanking, the indirect approach, to win battles quickly and

decisively. This was largely rejected following Napoleon’s defeat. Instead,

theorists such as Antoine Henri Jomini favored the direct approach, or mass-

ing troops for frontal attacks. Napoleon himself had adopted such tactics on

occasion during the later years of his career, most notably at the battle of

Borodino during the invasion of Russia in 1812. Jomini and others even

believed the spirited offensive could be successful against ﬁeld fortiﬁcations.

These post-Napoleonic writers were most inﬂuential until about 1840, dur-

ing the period when Mahan was studying in France, and most American

commentators adopted Jomini and his compatriots with enthusiasm.

One of these French theorists, Francis Gay de Vernon, a professor of

fortiﬁcation and the art of war at the Ecole Polytechnique, also urged the use

of ﬁeld fortiﬁcations to protect the army. Vernon argued that ﬁeldworks

should even be used to facilitate offensive action, as long as they were de-

signed so the attacking force had an opening in the works to debouch and

mass in the open for the assault. Vernon’s book on war and fortiﬁcation was

used at West Point from 1817 through 1830.

∞≠

6 Engineering War

Mahan was dedicated to the direct approach, but he signiﬁcantly revised

how it should be conducted. He argued that the poorly trained volunteer

force that the United States relied on to ﬁght its wars could not conduct suc-

cessful attacks on fortiﬁed positions unless the defending army was some-

how damaged ﬁrst. Even if U.S. volunteer troops were successful in attacking

a well-fortiﬁed position defended by a fresh army, the losses would be pro-

hibitive. Mahan believed the volunteers were more valuable to the country

as permanent civilians than as temporary soldiers. Moreover, the small regu-

lar army was too valuable to waste in frontal attacks on strong positions.

Mahan instead advocated what he called an ‘‘active defense.’’ First, use

ﬁeld fortiﬁcations to create a defensive position, entice the enemy to attack

it, and damage him signiﬁcantly. Then, follow up with a counterattack that

would be sure to take the enemy position and scatter or decimate the oppos-

ing army. This was a smart adaptation of prevailing French theory to the

peculiar conditions of the American military force. Whether it was practical

in the ﬁeld was another issue. The enemy would have to cooperate in de-

veloping such a scenario, and volunteers, who often were naively enthusias-

tic about attacking with little preparation, would have to be convinced of the

need to dig in before the ﬁrst shot was ﬁred.

∞∞

Despite these obvious limitations, Mahan was the only American military

theorist who offered an original twist on the European doctrine. Despite

Mahan’s prestige, his theory about the active defense was not uniformly

accepted among American ofﬁcers. It existed side by side with prevailing

French theory about the need to mass and attack directly without using

ﬁeldworks. West Point cadets and serving ofﬁcers were exposed to both

theories. Mahan’s followers made sure his views were kept active with the

passage of time. Henry W. Halleck’s solid book, Elements of Military Art and

Science (1846), praised Mahan’s theory as best suited to the peculiar charac-

teristics of the American soldier. James St. Clair Morton, a brilliant young

graduate of the academy, perpetuated Mahan’s theory in publications such

as Memoir on the Dangers and Defenses of New York City (1858) and Memoir

on American Fortiﬁcation (1859).

∞≤

Yet if one looks at the campaigns of the Mexican War from 1846 to 1848,

one would have to conclude that few American ofﬁcers paid attention to

Mahan’s theory. Repeatedly, American commanders assumed the tactical

offensive without digging in, and they usually made successful attacks. Even

on the rare occasion when American troops acted on the defensive, as at the

battle of Buena Vista, they failed to fortify. It is true that the Mexican War

could be taken as a sterling proof of the Jomini school of thought as it relates

Engineering War 7

to offensive tactics and the role of ﬁeldworks. But one would have to point

out that the Mexican army was not as dangerous a foe as most European

armies of the day, and not as dangerous as either the Northern or Southern

armies would be in the Civil War. Historians have noted that the Americans

came out of Mexico with a belief that a spirited attack can overcome ﬁeld

fortiﬁcations, for they had done so many times, but it must be noted that

such a lesson was unequally learned. Thomas J. ‘‘Stonewall’’ Jackson seems

to have come from the war with little regard for the usefulness of ﬁeldworks,

to judge by his lack of attention to them in the Civil War. But George Mc-

Clellan and others served equally well in Mexico and yet often resorted to

ﬁeld fortiﬁcations in the bigger war to come. Both Union and Confederate

armies in general used fortiﬁcations of all kinds far more frequently in the

ﬁrst half of the Civil War than their counterparts ever did in the Mexican

conﬂict.

∞≥

Lessons learned from the introduction of riﬂe muskets in the 1850s and

the experience of the Crimean War of 1854–56 were mixed. Mahan did not

believe that riﬂes would signiﬁcantly alter the validity of his theory, and

he pointed to the siege of Sebastopol as proof that armies needed to en-

trench for protection even if they planned offensive action. Historian Edward

Hagerman ﬁrmly states that the riﬂe musket revolutionized combat, and he

also argues that it invalidated the direct approach to attacking an enemy

position. He interprets McClellan’s commission report as sensing this change

in the reality of warfare. Hagerman believes that McClellan pointed out ‘‘that

the ﬁrst signiﬁcant use of riﬂe infantry weapons in the Crimean War shifted

the tactical balance from the open frontal assault to entrenched tactical

deployment.’’

∞∂

The role of the riﬂe musket in affecting the nature of tactics in the Civil

War is controversial. I disagree with Hagerman’s assessment on this matter

(see the Preface for my comments on the use of the riﬂe musket). In short,

there is, in my view, no evidence that riﬂed small arms signiﬁcantly affected

the success or failure rate of frontal assaults or led to the increased use of

ﬁeld fortiﬁcations. Moreover, my reading of McClellan’s report does not

support the view that the young captain recognized such a shift. McClellan

did note that the Russian ﬁeldworks around Sebastopol were strong and well

designed. But he also pointed out that they were little more than ‘‘inert

masses’’ unless defended by highly motivated infantrymen and artillerymen.

McClellan rejected the prevailing opinion of his day that Sebastopol demon-

strated the greater value of temporary ﬁeldworks over permanent works. It

merely demonstrated that ‘‘temporary works in the hands of a brave and