Introduction to Union Organisations – Theatres

Introduction to Union Organisations – Theatres

Go to Western Territories and Pacific Coast Theatre / Pacific Coast Theatre / Trans-Mississippi, Northwest, and Frontier Theatres / Western Theatre / Gulf Coast Theatre / Eastern Theatre / Capital and North-Eastern Theatre / Atlantic Coast Theatre for detailed summaries.

Read the summaries below about:

Pre-War Organisations
Western Territories and Pacific Coast Theatre LINK
Trans-Mississippi, Northwest, and Frontier Theatre LINK
Gulf Coast Theatre LINK
Atlantic Coast Theatre LINK
Eastern Theatre LINK
Capital and Northeastern Theatre LINK
Western Theatre LINK
Post-War Organisation

Pre-War Organisation

The United States Regular Army was ill-prepared for a war on a continental scale and was organised primarily for operations on the western frontier. There were 198 companies formed into 10 Regiments of Infantry, 4 Regiments of Artillery and 5 Regiments of Cavalry. There were 1,098 Officers and 15,304 Enlisted Men of whom 727 Officers and 13,930 Enlisted Men were present for duty. The majority of field forces were deployed along the western frontier and in the new territories. Garrisons were also located in the primary east coast ports where a new generation of coastal fortifications was under construction. These forts were not fully garrisoned but were held ready for occupation by the State Militia in the event of war with a European power. Of the 198 available companies or batteries, 183 were stationed at 79 different posts west of the Mississippi. The other fifteen companies, mostly artillery, were allocated to coastal fortifications, 23 arsenals and the Canadian border.

Historically, for major campaigns such as the War with Mexico in 1846-1848, the United States had supplemented its Regular Army by recruiting a temporary army of volunteers, called up for service of limited duration. In the coming Civil War, these US Volunteers would, as before, form the backbone of the forces engaged. This applied also to the in frontier and far western territories as Volunteer troops were raised to replace or augment the Regular Army troops recalled for service against the Confederacy.

The six military Departments after 15 January 1861 reported the following numbers available of men for duty:

Department of the East 3,894
Department of the West 3,585
Department of Utah 685
Department of the Pacific 3,382
Department of New Mexico 2,624
Department of Texas 2,258.

The Department of the East manned the eastern coast fortifications with 18 artillery companies and one company of engineers but no infantry or cavalry. Only staff bureaux were stationed in the vicinity of Washington, DC. The Department of Utah had three companies of dragoons, three companies of artillery, and four companies of infantry. Thirteen companies of infantry and two companies of dragoons were in the Department of New Mexico and one regiment of infantry was in the Department of Texas. There were forces also in the Department of California and the Department of Oregon.
The seven Departments at the start of 1861 were reduced on 15 January 1861 to six by combining the Department of California and the Department of Oregon into a single new Department of the Pacific.
The imminence of war and the vulnerability of the capital region required the creation of the Department of Washington on 9 April 1861. This was the first military organisation established specifically to conduct military operations against the Confederacy.

Western Territories and Pacific Coast Theatre.

This theatre broadly covers the state of California, the Arizona Territory, Colorado Territory, Dakota Territory, Nevada Territory, New Mexico Territory, Oregon Territory, Utah Territory, and adjacent operational regions.
At the outbreak of war, the Department of Utah, Department of New Mexico, and the Department of the Pacific were responsible for the area. In July 1861, the Department of Utah was discontinued, and its territory brought under the Department of the Pacific. Utah transferred to the Department of the Missouri in February 1865 and was never again reconstituted as a military Department.
The Department of New Mexico was also discontinued in July 1861 and its territory transferred briefly to the Western Department. The Western Department proved to be torn between its westward and eastward facing responsibilities, so the Department of New Mexico was re-established in November 1861, after the dissolution of the Western Department.
The Department of the Pacific and the revived Department of New Mexico, and their Districts, shared military authority in the Far Western theatre. The District of Colorado was attached only as an administrative convenience from September to October 1862 during the recreation of the Department of the Missouri.
Both the Department of the Pacific and the Department of New Mexico were discontinued in the post-war reorganisation of 27 June 1865. The territory of the former was divided into the Department of California and the Department of the Columbia, and the territory of the latter was divided between the Department of the Pacific and the Department of the Missouri.

Trans-Mississippi, Northwest, and Frontier Theatre

This theatre broadly covers the states of Arkansas, Iowa, Kansas, Missouri, Wisconsin, Minnesota, Nebraska, Indian Territory, and adjacent operational regions.
Most of the region between the Mississippi River and the Rocky Mountains had been under the control of the Department of the West. In July 1861, this was renamed as the Western Department and underwent political and military turmoil while the pro-Southern commander, Brigadier-General William Selby Harney, was supplanted. In the short term, Nathaniel Lyon provided bold leadership, but he was soon transferred to the prominent figurehead John Charles Frémont. By November, it was clear that Frémont was ineffective, if not incompetent, and he was replaced by David Hunter in November 1861. During this time, the Department had absorbed the former Department of New Mexico to the west, giving it a confusing eastward and westward facing responsibility.
More importantly, from its headquarters at St Louis, Missouri, the Western Department also attended to the strategically vital region around the confluence of the Missouri, Mississippi, and Ohio Rivers. Almost immediately, the unwieldy and disparate command was rationalised in response to that urgent strategic priority and Major-General Henry Wager Halleck took control. The newly created Department of the Missouri reflected Halleck’s attention on the great rivers from November 1861 until September 1862. While operations continued west of the Mississippi, requiring the creation of numerous Districts, the more decisive actions occurred east of and along the Mississippi, and along the Tennessee River. Straddling two theatres and laying the foundations for subsequent operations between the Mississippi and the Appalachians, the evolution of the Department of Missouri is continued temporarily in Part 3g, the Western Theatre as part of the gigantic Department of the Mississippi, the equivalent of a Military Division, created under Halleck in March 1862.
Kansas became a District of the Department of the Mississippi from March to May 1862 but soon regained its autonomy as the priorities along the frontier evidently diverged from the more conventional actions along and east of the Mississippi. Hunter led the Department until March 1862, when James Gilpatrick Blunt took over the District and then the revived Department. Blunt commanded until the next major reorganisation in September 1862, when the Department of the Missouri regained its earlier focus west of the Mississippi.
In September 1862, the Department of the Missouri was a reorganised and Department of the Northwest created to manage operations in the Trans-Mississippi, Northwest, and Frontier Theatre. Relevant territories were detached from the discontinued Department (Military Division) of the Mississippi and Department of Kansas was discontinued, enabling a more coherent approach to command in the theatre. The Department of the Northwest – led almost continually by Pope -dealt primarily with actions against Native Americans. The Department of the Missouri primarily prosecuted operations against the Confederates and their supporters west of the Mississippi under Curtis, Schofield, and then Rosecrans.
The Department of the Missouri and Department of the Northwest remained the primary commands in the region until January 1864 when the southward advance through Confederate territory necessitated a further reorganisation. The Department of Kansas was recreated to attend to the frontier regions and a new Department of Arkansas was added to manage operations against Confederate-held territory.
As the Union advance against the Confederacy was pressed increasingly into the Trans-Mississippi region from Louisiana, the Department of the Missouri and the Department of Kansas were transferred to a new Military Division of West Mississippi (Trans-Mississippi Military Division). This achieved coordination of effort against the Confederates west of the Mississippi. The Department of Kansas and Department of the Northwest continued with their operations aligned towards Native American affairs and against unconventional pro-Confederate forces.
By January 1865, the Confederate were incapable of extensive operations west of the Mississippi and Union attention returned to the Gulf Coast and east of the Mississippi. When the Military Division of West Mississippi (Trans-Mississippi Military Division) was disbanded the Department of the Missouri and the Department of the Northwest were transferred to their own Military Division of the Missouri, with the Department of Kansas again being discontinued, and taken over by the Department of the Missouri. The Department of Arkansas was connected more to operations by the Military Divisions that managed the Gulf Coast states from Texas to Alabama and so it only joined the Military Division of the Missouri from March to May 1865.

Western Theatre

This theatre broadly covers the states of Illinois, Indiana, Ohio, Kentucky, Tennessee, Mississippi, and adjacent operational regions in Alabama, Georgia, South Carolina, and North Carolina.
This was the decisive theatre of operations where the foundations of Union victory were established. Being geographically central, operations in this theatre inevitably impinged on and overlapped with all the other theatres of war. The military organisation therefore experienced a complex evolution as attention was frequently diverted to diverging and tangential operations. Nevertheless, the main focus remained on two main lines of advance by the Union Army, both assisted by naval forces on the inland rivers. The first followed the line of the Mississippi southwards and the second followed the line of the Tennessee River into northern Georgia from 1862 to 1864. The exploitation of the latter advance in late 1864 and 1865 took dominant Union forces from the western theatre across Georgia to the Atlantic Coast and then north through the Carolinas.
The first attempt to bring these extensive operations under a unified command was comparatively short-lived. The Department of the Mississippi was created in March 1862 to command operations in states bordering the Mississippi, Tennessee, Cumberland, and Ohio Rivers. The occupation of Missouri, Kentucky, and Western Tennessee was largely accomplished, although those areas remained under continual threat of raids and reconquest. This supreme command was dissolved into its constituent departments in September and October 1862 as the objectives of each region once again diverged.
A unified command structure was more fully achieved in October 1863 with the creation of the Military Division of the Mississippi. This development became possible after control of the Mississippi River was achieved during the summer and attention concentrated on the line of invasion along the Tennessee River and into Georgia, with operations in eastern Tennessee subordinated to it. The inexorable progress of the armies of the Military Division through Georgia in 1864, and into the Carolinas in 1865 during brought those regions, and their Departmental commands in the Atlantic Coast Theatre, within its sphere of operational control but not necessarily its administrative control.

Gulf Coast Theatre

This theatre broadly covers the states of Texas, Louisiana, Alabama, Florida, and adjacent operational regions.
The outbreak of war found only isolated outposts still in the hands of the Federal authorities and all but one of these were quickly taken over by the Confederates with varying degrees of resistance. The important Department of Texas continued in nominal existence until November 1862 despite there being no organised military force in the state since April 1861.
The exception was Fort Pickens near Pensacola, Florida. And a new Department of Florida was established almost immediately after the outbreak of hostilities with headquarters at Fort Pickens. Theoretically, the Department was responsible for the entire state of Florida although the fort was the only Union-occupied ground. By 11 January 1862, sufficient progress had been made to establish the Department of Key West to oversee the western Florida coast and islands.
The Department of the South was established in March 1862 and took control of the Department of Florida and the Department of Key West, each of which was reduced to a District of that Department. Responsibility for western Florida and the coastal section of Alabama alternated between the Department of the Gulf and the Department of the South, depending on the evolving military situation and progress of operations.
The seizure of New Orleans in early 1862 led to the capture of much of Louisiana and enabled Union warships to penetrate inland up the Mississippi and Red Rivers, assisting the army as it gradually took control of the lower Mississippi by July 1863. The Department of the Gulf was established under B F Butler in February 1862, to direct the operations in Louisiana. The coast of Texas was added officially in November 1862, coinciding with the appointment of N P Banks to replace B F Butler. As new territory was captured, Districts were set up to direct local operations. The Department of the Gulf was the primary authority for operations in the theatre until the end of the war, and its main field force was known as the Army of the Gulf. The bulk of the army was transported from the North by the Navy, but they were increasingly supplemented by detachments coming southwards along the Mississippi and forces recruited locally from freed slaves.
In May 1864 the failed advance towards Texas from the north (Arkansas) and east (Louisiana) proved the need for strategic coordination of operations west of the Mississippi. As a result, the Military Division of West Mississippi (Trans-Mississippi Military Division) was created, responsible for the Department of the Gulf, the Department of Arkansas, and the Department of the Missouri. By the end of 1864 attention was being directed east of the Mississippi and the Department of the Mississippi was added to the Military Division in November 1864. In January 1865, as the objective switched more intensively towards Mobile Bay and the Alabama Coast, the Department of the Missouri (January 1865) was detached, to be followed by the Department of Arkansas in March 1865. After combining all available field forces in a new Army of West Mississippi in February 1865, the campaign was begun against Mobile. The Districts around Mobile were transferred temporarily from their Departments to the direct control of the Military Division for the same operational reasons.
In May 1865 the purpose of the Military Division was complete, and it was discontinued. The Department of the Gulf operated independently from May 1865, however, it passed control over Louisiana and Texas to the new Military Division of the Southwest as a show of strength was presented to the French authorities in Mexico. The Department retained its authority in Mississippi, and coastal parts of Alabama and Florida until the post-war reorganisation of 27 June 1865, when it ceased to exist.

Atlantic Coast Theatre

This theatre broadly covers the states of Florida, Georgia, South Carolina, North Carolina, and adjacent operational regions.
Activity in the theatre grew through the gradual acquisition of bases along the coasts of Florida, Georgia, South Carolina, and North Carolina. The western parts of Florida passed between this theatre and the Gulf Coast Theatre, depending on operational requirements. Being isolated by sea from the contiguous mass of Union territory, the military outposts in this theatre were enabled and sustained by the Navy. The aim was to secure bases of operations to maintain the naval blockade and for the army to advance to capture ports that would provide secure supply lines and into the hinterland. It was not until mid-1864 for Virginia, the end of 1864 for Georgia and South Carolina, and early 1865 for North Carolina that these operational territories meshed with the forces advancing overland from the north, west, and south.
The retention of Fortress Monroe in Virginia at the outbreak of hostilities provided the first avenue to penetrate the interior, along the Yorktown Peninsula and James River. Created as early as May 1861, the Department of Virginia continued to control the Virginia coastline until July 1863. In spring 1862, it became part of the operational territory of the main eastern army in Virginia but regained its autonomy in summer 1862 as those operations ended in a withdrawal of the bulk of the field forces from the outskirts of Richmond. By July 1863 it was extended to become the Department of Virginia and North Carolina, in order to assure unity of command for the coastal garrisons of Virginia and North Carolina. In mid-1864, its active operations could be synchronised with the Eastern army which was approaching Richmond overland from the north.
The Department of North Carolina was founded first January 1862, to direct operations along the North Carolina Coast. This was followed in March 1862 by the creation of the Department of the South which operated along the South Carolina and Georgia coasts, and to varying degrees, in Florida.
The Department of the South was established in March 1862 and took control of the Department of Florida and Department of Key West, each of which was reduced to a District of that Department. Responsibility for western Florida and the coastal section of Alabama alternated between the Department of the Gulf and the Department of the South, depending on the evolving military situation and progress of operations. The Department of the South remained active until June 1865.
The Department of North Carolina and the Department of Virginia were incorporated into the Department of Virginia and North Carolina from July 1863 until January 1865, when their strategic objectives diverged. The Department of Virginia was separated for the final operations of the eastern armies around the Confederate capital. The northward advance of the Union armies through Georgia and South Carolina brought North Carolina under the aegis of the Military Division of the Mississippi to provide unity of command.

Eastern Theatre

This theatre broadly covers the states of Virginia, and West Virginia, the District of Columbia, and adjacent operational regions.
Before the war, the Department of the East covered the entire region east of the Mississippi, but it was rapidly diminished as new territorial commands were established in its former territory (e.g., Departments of Florida, Washington, Annapolis, Pennsylvania, Maryland, the Ohio, Virginia, Northeastern Virginia, Kentucky, the Shenandoah, the Potomac, Western Virginia, New England, and several more evolving in the western theatre).
In October 1861, the Department of the East was renamed as the Department of New York, reflecting its reduced scope. It was revived as the Department of the East in January 1863 to manage recruitment and administrative matters, as well as civil disorder. In the meantime, within this reduced theatre, the Department of New England existed briefly from October 1861 to February 1862, primarily as vehicle for recruiting and organising new military forces.
Operations in the eastern theatre were dominated by the fact that the two capitals at Washington, DC, and Richmond, Virginia, were barely one hundred miles apart. Virginia inevitably became a primary theatre of the conflict as each belligerent sought to threaten the other’s capital city while defending its own. Each side had to provide for the defence of its capital, but the urgency was greater on the Union side, tying down large forces to occupy Washington’s extensive fortifications and to counter Confederate diversions and threats. This theatre of command was the constant obsession of the government, the press, and the people.
The Union had to take the strategic initiative and attempted several overland advances towards Richmond, with occasional efforts made from the coast along the James River and Yorktown Peninsula. The Confederates responded aggressively and made diversionary advances and invasions towards Washington and across the Potomac River into Union territory. This required the Union to make continual adjustments to the military organisation north of the Potomac, which could raise short-term forces, forestall, react to raids, and provide security for the Northern hinterland.
At times Union forces based on either side of the James River synchronised their operations with the main Army of the Potomac, but more frequently they were focused on guarding and extending the garrisons established along the Virginia and North Carolina coasts. They could harass and make diversionary operations, but it was not until Spring 1864 that the integration of overland and coastal operations was accomplished. The primary instrument for action in this sector was the Department of Virginia, initially established on 22 May 1861 only to hold Fortress Monroe but expanding to become a major force. In July 1863 it was merged with the Department of North Carolina into a new Department of Virginia and North Carolina so that operations along the Atlantic coast and rivers in both states could be coordinated more efficiently.
Both sides engaged continually in operations in the Shenandoah Valley and the mountainous region of western Virginia. The Valley was an important source of supplies for the Confederates and offered a covered line of advance into Union territory, an advantage that was exploited effectively in 1862, 1863, and 1864. The general south-westward orientation of the valley meant that any Union advance would gradually diverge and dissipate forces away from the main axis between Washington and Richmond.
Western Virginia was largely pro-Unionist and provided a base for Union operations towards prized natural resources and the vital East-West railroad line through eastern Tennessee and southwestern Virginia. The region was inaccessible to large forces and difficult either to occupy or defend but it constantly drew the attention of both sides. Difficult to conquer and garrison, there were many intense but short campaigns and raids. It was only in late 1864 and early 1865 that the Union forces were able to move in force out of the mountains into eastern Tennessee, southwestern Virginia, and western North Carolina.
The defence of the national capital was always a sensitive issue as its loss would have led to disastrous political and diplomatic consequences. The Department of Washington was founded immediately in April 1861. In July 1861 it was subordinated to the Military Division and then converted into a District of the Department of the Potomac, to ensure that the security of the capital remained an integral responsibility for the main field forces in the eastern theatre. In February 1863, it was reinstated as the Department of Washington with its own Districts established for the defence of, and to provide logistical services around, the capital.
In the immediate crisis of the outbreak of war, short-lived organisations were formed partly in response to immediate or perceived threats and partly to provide a focal point for recruitment and training. These included the Department of Pennsylvania and the Department of the Shenandoah from April to August 1861, and the Department of Annapolis and its successor Department of Maryland from April to July 1861. These were swept away by McClellan as he consolidated centralised command in his Military Division, later Department of the Potomac. The field forces gathered for the first advance into Virginia in the early months of the war were assigned to the Department of Northeastern Virginia on 27 May 1861 as the Army of Northeastern Virginia, and it was clearly differentiated from the capital’s defence force. After the defeat at First Bull Run, in July 1861, the Military Division of the Potomac replaced the Department. In August 1861, the Department of the Potomac, and the Army of the Potomac, which was always the Union’s largest single field force, were created and remained operational until June 1865.

Capital and North-Eastern Theatre

This theatre broadly covers the northeastern states of Connecticut, Maine, Massachusetts, New Hampshire, New York, New Jersey, Rhode Island, and Vermont, along with the territorial commands around the District of Columbia in Maryland, Delaware, and Pennsylvania.
The New England states saw few active operations on their soil but were nevertheless important in maritime and recruiting activities. Where military activity did impinge on their territory in Pennsylvania, Delaware, Maryland, and around the capital district, they were generally assigned to an appropriate territorial command.

Post-War Organisations

After the end of hostilities, the US Army High Command was reorganised so that every part of the continent came under the control of one of the five newly designated Military Divisions. The Military Division of the Pacific took over the west coast states and far western territories. The Military Division of the Southwest became the Military Division of the Gulf in June 1865 to cover the Gulf Coast states. The Middle Military Division was merged into the Department of the Military Division of the Atlantic, and took over the eastern and southeastern states. The Military Division of the Missouri controlled the midwestern and northwestern states and the frontier territories. The Military Division of the Tennessee took over some of the former Confederate states of the western theatre.
This following structure of 31 December 1865 down to the Department level, remained largely intact for many years although some commanding officers with US Volunteers grades soon mustered out of service, and either reverted to their Regular Army grade or were replaced by Regular Army officers.

General–in-Chief: Lieutenant-General USA Ulysses Simpson Grant

Military Division of the Atlantic: Major-General USA George Gordon Meade
Department of the East: Brigadier-General USA & Major-General USV Joseph Hooker
Middle Department: Brigadier-General USA & Major-General USV Winfield Scott Hancock
Department of North Carolina: Brigadier-General USV Thomas Hewson Ruger~
Department of South Carolina: Major-General USV Daniel Edgar Sickles
Department of Virginia: Brigadier-General USA & Major-General USV Alfred Howe Terry
Department of Washington: Major-General USV Christopher Columbus Augur

Military Division of the Gulf: Major-General USA Philip Henry Sheridan
Department of Florida: Major-General USV John Gray Foster
Department of Louisiana: Major-General USV Edward Richard Sprigg Canby
Department of Texas: Major-General USV Horatio Gouverneur Wright

Military Division of the Mississippi: Major-General USA William Tecumseh Sherman
Department of the Missouri: Brigadier-General USA & Major-General USV John Pope
Department of the Ohio: Major-General USV Orlando Bolivar Willcox
Department of the Tennessee: Major-General USV George Stoneman

Military Division of the Pacific: Major-General USA Henry Wager Halleck
Department of California: Brigadier-General USA & Major-General USV Irvin McDowell
Department of the Columbia: Colonel Charles Swain Lovell

Military Division of the Tennessee: Major-General USA George Henry Thomas
Department of Alabama: Brigadier-General USV Charles Robert Woods
Department of Georgia: Major-General USV James Harrison Wilson
Department of Kentucky: Major-General USV John McAuley Palmer
Department of Mississippi: Major-General USV Thomas John Wood

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