Editing Union army (section)

===Corps of Engineers===
{{Main|United States Army Corps of Engineers}}
The Corps of Engineers was a small part of the army prior to the Civil War but played an important role not only in the conflict but for the nation as a whole.  The Corps was responsible for running the [[United States Military Academy]] at [[West Point, New York|West Point]], which supplied officers to all branches but whose top graduates were commissioned into the Corps. They were not only involved with [[military engineering]] such as constructing [[fortifications]] and harbor defenses but also oversaw [[civil engineering]] including building canals, bridges and similar projects. This focus on civil works did prevent the Corps from devoting its entire effort to the war though.<ref name="Newell292">Newell & Shrader, p. 285–292</ref><ref name="Baldwin18">Baldwin, W. (2008). ''The U.S. Army Corps of Engineers: A History''. United States: Headquarters, U.S. Army Corps of Engineers, Office of History. p. 15–18</ref> Corps personnel acted as [[combat engineer]]s during battle, helping to construct [[pontoon bridge]]s, repair roads and bridges, dig [[Trench warfare|trenches]], and conduct [[Engineer reconnaissance|reconnaissance]]. The Corps also exerted an influence beyond its small size as many of the Union's most prominent officers, including McClellan and Meade, were themselves trained as engineers and used their knowledge to influence the outcome of battles.<ref name="Newell292" /><ref name="Baldwin110">Baldwin, p. 107–110</ref>

Prior to the war, the Corps of Engineers consisted of just forty-eight officers and a single company of 150 engineer troops.  Engineer Company A was first created for the [[Mexican–American War]] and guarded President Lincoln at his [[First inauguration of Abraham Lincoln|first inauguration]].<ref name="Newell292" /><ref name="Baldwin110" /> It was organized with ten sergeants (master-workmen), ten corporals (overseers), two musicians, sixty-four first-class privates ([[Armed-forces artificer|artificers]]) and sixty-four second-class privates (laborers).<ref>Callan, J. F. (1864). The Military Laws of the United States, Relating to the Army, Volunteers, Militia, and to Bounty Lands and Pensions, from the Foundation of the Government to 4 July 1864: To which are Prefixed the Constitution of the United States (with an Index Thereto,) and a Synopsis of the Military Legislation of Congress During the Revolutionary War. United States: G.W. Childs. p. 24–25</ref> In August 1861 Congress authorized the formation of three more companies to be organized the same as Engineer Company A, with all four organized into a single battalion (the US Engineer Battalion, later [[1st Engineer Battalion (United States)|1st Engineer Battalion)]], and the addition of two lieutenant colonels, four majors and six lieutenants to the Corps. The battalion had no formal headquarters but fell under the command of the most senior officer present. In March 1863, when the Corps of Topographical Engineers was disbanded and its function merged with the Corps of Engineers, Congress further revised the Corps to consist of a brigadier-general as Chief Engineer, four colonels, ten lieutenant-colonels, twenty majors, thirty captains, thirty first lieutenants and ten second lieutenants.<ref name="Newell292" /><ref name="Baldwin110" />

The US Engineer Battalion served ably as part of the Army of the Potomac, but on its own was insufficient to see to the army's need for engineers throughout the different theaters of war. A small number of volunteer engineer regiments were formed during the war, including the [[1st Michigan Engineers and Mechanics Regiment]], the [[1st New York Engineer Regiment]] and the [[1st United States Veteran Volunteer Engineer Regiment]]. However, in many cases engineering work was carried out by line soldiers under the supervision of officers with engineering backgrounds, if any were available.<ref name="Newell292" /><ref name="Baldwin110" /> Most types of engineering work, such as digging simple [[Earthworks (military)|earthworks]] or laying small bridges, did not require the specialized skills of engineers, which were required for complex endeavors like constructing pontoon bridges or forts. Union armies typically detailed soldiers to form company-sized detachments of [[Pioneer (military)|pioneers]] to repair roads or bury the dead after a battle.<ref>Hess, E. J. (2005). ''Field Armies and Fortifications in the Civil War: The Eastern Campaigns, 1861–1864'' (Civil War America). United Kingdom: University of North Carolina Press. p. 15–16</ref>
;Leadership
*[[Joseph Gilbert Totten]]: December 7, 1838{{spaced ndash}}April 22, 1864
*[[Richard Delafield]]: April 22, 1864{{spaced ndash}}August 8, 1866