U.S. Corps of Topographical Engineers

Engineers in the Union Army, 1861 - 1865

By Phillip M. Thienel*

Part I. Engineer Organization


At the outbreak of the Civil War the Corps of Engineers consisted of 43 officers and a company of 100 engineer soldiers. At the same time the Regular Army consisted of approximately 16,400 officers and enlisted men. These troops were augmented by the calls on April 15, 1861, for 75,000 militia and on May 31, 1861, for 500,000, but this still left the Union Army deficient in engineer troops. And although on May 4, 1861, the Regular Army was increased by ten regiments -- eight infantry, one cavalry, and one artillery -- no additional engineer units were authorized.

On August 3, 1861, Congress authorized three additional engineer companies and 6 additional lieutenants for the Corps of Engineers and 6 for the Corps of Topographical Engineers. Each company was to consist of 150 enlisted men, comprising 10 sergeants, 10 corporals, 2 musicians (fifer and drummer), 64 privates first class or artificers, and 64 privates second class. This set the authorized strength of the Corps of Engineers at 49 officers and 550 enlisted men. Another act, on August 6, 1861, added 2 lieutenant colonels and 4 majors.

Losing its officers to the volunteer forces complicated the problem of the Corps of Engineers because, during the period 1861-1865, only 117 officers actually held commissions in the Corps. The :majority of the officers were commanding regiments, brigades, divisions, corps, and even armies and departments. Besides, 37 were listed as war casualties. There was also the anomalous situation of only 3 officers from the Corps of Engineers commanding engineer units. These units were: The Engineer Brigade, Army of the Potomac; the Engineer Battalion, Army of the Potomac; and the 1st Veteran Volunteer Engineer Regiment, Army of the Cumberland. The report of the Chief of Engineers for the year ending June 30, 1864 showed that of the 86 officers presumably available for duty, 19 were commanding troops; 24 were engaged on seacoast defenses; 1 on lake surveys; 1 on naval site selection in the west; and 2 were assigned in the office of the Chief of Engineers. This left 39 engineer officers for duty as staff engineers with the armies and corps in the field.

Maj. Gen. Harry W. Halleck, the General-in-Chief of the Army, pointed out the ironical situation of a first lieutenant serving as army engineer in one of the largest armies. Halleck was discussing a bill to expand the Corps of Engineers. One of his proposals was to give the chief engineer of a field army the rank of colonel; of an army corps the rank of lieutenant colonel or major; and of a division the rank of major, captain or lieutenant.

As passed by the Congress on March 3, 1863, a bill called for the Corps of Topographical Engineers to merge with the Corps of Engineers and the latter was authorized 105 officers of which the former supplied 48. It also called for an additional company of topographical engineer soldiers (never organized) to bring the authorized enlisted strength to 855 men. This was the last instance of legislation affecting the Corps of Engineers during the Civil War. The four companies of engineer troops, known as the Engineer Battalion, served during the entire Civil War in the Army of the Potomac.


The act of July 17, 1862, provided that regiments and companies previously mustered into the service as volunteer engineers, pioneers or sappers and miners, and those that had been mustered into the service as infantry and were later recognized and employed as engineers, pioneers or sappers and miners, were to be accepted as volunteer engineers on the same footing in all respects in regard to their organization, pay, emoluments, and benefits, as the Corps of Engineers of the Regular Army. A War Department special order directed that the regiments of volunteer engineers were to be composed of twelve companies with 1 colonel, 1 lieutenant colonel, 3 majors, 1 adjutant, 1 quartermaster, 1 chaplain, 1 surgeon, 2 assistant surgeons, 1 hospital steward, 3 quartermaster sergeants, and 3 commissary sergeants. Each company was authorized 4 officers and 150 enlisted men with the same table of organization as the company of the Corps of Engineers. Essentially, this act did nothing more than confirm the fact that volunteers were serving as engineers. According to the records, no additional volunteer engineer units were organized and no additional volunteer units were delegated engineer functions after the passage of this act. The units affected by this act were:

1st New York Volunteer Engineer Regiment, Col. Edward W. Serrell, was a three-year unit. It served with the Department of the South and the Army of the James.

15th New York Volunteer Engineer Regiment. This two-year regiment entered the service as an infantry regiment under the call for volunteers in 1861 and later was designated an engineer unit. It served with the Army of the Potomac.

50th New York Volunteer Engineer Regiment. This three-year regiment entered the service as an infantry regiment under the call for volunteers in 1861 and was later designated an engineer unit. It also served with the Army of the Potomac.

1st Michigan Engineers and Mechanics Regiment entered the service under the call for volunteers in 1861 for a period of three years. It served with the Army of the Ohio, the Department of the Cumberland, and with General Sherman in the Military Division of the Mississippi.

1st Missouri Engineers, frequently called the Engineer Regiment of the Westentered the service under the call for volunteers in 1861 for a period of three years. It served with the Army of the Mississippi, Army of the Tennessee, and with General Sherman in the Military Division of the Mississippi.

The Independent Company of Engineers and Mechanics, Kentucky (Captain William F. Patterson's Company) was mustered into the service on September 25, 1861, for three years, at Cumberland Gap, Kentucky. It served in Cumberland Gap, and in the Mississippi Valley. The strength of this company never exceeded 43 officers and enlisted men.

Engineer Company, Pennsylvania. Authorized on June 2, 1862, this company reported to Washington, D. C., during the summer of 1862. It constructed 6 miles of defenses on the Virginia side of the Potomac River from Chain Bridge south to Fort Albany, near Alexandria. After the Battle of Antietam, the company was transferred to Harpers Ferry, where it built several bridges for the advance of the army into the Loudon Valley. It also constructed a suspension bridge over the Shenandoah River. The headquarters of the company remained in Harpers Ferry during the war although detachments were sent out on various duties, such as keeping the bridges over the Potomac River in order. On June 20, 1865, this company was mustered out of the service.


The 1st Veteran Volunteer Engineer Regiment was organized August 30, 1864, by Col. William E. Merrill, under the Act of Congress of May 20, 1864, which authorized the enlistment for three years of any enlisted man who had served or was serving as a pioneer, pontonier or engineer. The regiment served with the Army of the Cumberland.

On March 3, 1865, Congress authorized five more Veteran Volunteer Engineer Regiments to be organized with twelve companies each and authorized two additional companies for Colonel Merrill's regiment. Before they could be organized the war ended.

The Corps d' Afrique, organized from negroes in Louisiana, is first mentioned in June 1863 in the form of an order issued by the Department of the Gulf designating the First Regiment of Louisiana Engineers as the First Regiment of Engineers of the Corps d 'Afrique. In August 1863 an abstract of the strength return of the Department of the Gulf reported that the 2d and 3d Regiments of Engineers of the Corps d 'Afrique had been organized. On December 31, 1863, the records showed that the 4th Regiment had been organized prior thereto, and that the 5th Regiment of Engineers of the Corps d' Afrique was activated in the early part of 1864. The Department of the Gulf issued a general order on April 19, 1864, to the effect that the five regiments of engineers of the Corps d' Afrique were to be designated the 95th to 99th Infantry Regiments. A week later these regiments were directed to perform engineering duties under the chief engineer, Department of the Gulf, under whose jurisdiction they remained during the war.

Pioneer and pontonier units were also established by the field commanders in the Union Army. Although at times these units were under the command of engineer officers, they were not actually engineer units. The Army of the Potomac fixed the strength of the pioneer organization at 2 per cent of the effective force of the infantry brigade. A captain was detailed by the division commander to command the pioneers who carried axes, shovels, and picks, and whose duty was to construct and repair roads, bridges, and temporary defenses.

In the Shenandoah Valley in June 1862, Captain Mapes' Pioneers were organized by the detail of 50 men from the participating infantry regiments to repair the bridges between Front Royal and Strasburg, Virginia. The Army of the Cumberland organized a Pioneer Corps by the detail of 2,685 pioneers from the infantry regiments under the command of Capt. James St. Clair Morton, Corps of Engineers. This pioneer corps was divided into four battalions for duty with the 14th, 20th, and 21st Corps. Capt. Peter C. Hains, Corps of Engineers, for a short time commanded a pioneer brigade, which included the 1st Pontoniers, organized about March 1864, in the Department of the Gulf. The records donot state whether this unit was composed of engineers or pioneers. When Sherman marched from Chattanooga in 1864 the 58th Regiment Indiana Volunteer Infantry was detailed as the pontoniers for one wing of the army. In the raid of Wilson's Cavalry into Northern Alabama in 1865, a detachment of the 12th Missouri Cavalry was detailed as pontoniers.


The actual and authorized engineer organizations of the Union Army during the Civil War were:



Type of
Actual Authorized
Company, Volunteer 2 2 150
Battalion, Regular 1 (5 Cos) 1 (4 Cos) 750
Regiment, Volunteer
(12 Cos)
5 5 1,800
Regiment, Veteran
Volunteer (12 Cos)
5 1 1,800
95th, 96th, 97th, 98th and 99th Infantry (colored) 5 5 1,800


*  Thienel, Phillip M., 1955.  Engineers in the Union Army, 1861--1865:  Military Engineer, vol. 47, nos. 315-316.






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