XXII Corps ( Union Army ) XXII Corps was a corps in the Union Army during the American Civil War . It was created on February 2 , 1863 , to consist of all troops garrison ed in Washington , D . C . , and included three infantry divisions and one of cavalry ( under Judson Kilpatrick , which left to join the Army of the Potomac during the Gettysburg Campaign ) . Many of its units were transferred to the Army of the Potomac during Grant ' s Overland Campaign . This Corps did not include the many regiments that passed through Washington , D . C . on the way to the front or away from it . Nor does it include the many regiments from the Army of the Potomac , Army of Georgia , and Army of the Tennessee that encamped in the area to participate in the Grand Review of the Armies . History . Civil War Armies at the time took their name from the Department that it was born out of . This is the reason for the naming of the Army of the Potomac , born out of the Department of the Potomac . At the time of the war , the Union named most of its departments , and thus its armies , after naturally occurring landmarks , specifically water courses , i . e . The Army of the Potomac , The Army of the James , The Army of the Gulf , etc . In opposition , the Confederacy named most of their Armies for geographic areas and states . Department of the East . Comprising all of the United States east of the Mississippi River , about half of which became Confederate territory . Formed on January 1 , 1861 , there were many Departments formed within its borders , and finally destablished August 17 , 1861 . Its primary focus was to employ a chain of command to all units until the smaller departments could be formed . Headquartered in Albany , New York , it was commanded by Major General John E . Wool . Department of Washington , D . C . . Constituted April 9 , 1861 , to include Washington , D . C . to its original boundaries of Arlington , Virginia , and the state of Maryland as far as Bladensburg . It was formed to center on the defense of the national capital , and to differentiate it from the Department of the East . The department was commanded by Lieutenant Colonel Charles F . Smith from April 10 through April 28 , 1861 , and Colonel ( later Brigadier General ) Joseph K . Mansfield from April 28 , 1861 , through the Department ' s dissolution on July 25 , 1861 . Department of the Potomac . The Department of the Potomac , formed July 25 , 1861 and destablished August 16 , 1861 , provide for the defense of the city of Washington , D . C . This Department was entrusted with the duty of protecting the United States ' capital , with the and the construction of fortifications . Before the dissolution of the Department of the Potomac , most of the fortifications in the Washington , D . C . , area were constructed , mainly by the regiments that were garrison ed there , most of whom had gone on to form the Army of the Potomac . Commanded by Major General George B . McClellan . Military District of Washington . A Military District during the Civil War was a formation within a Department for the purpose of reporting directly to the department commander for administrative affairs . The Military District of Washington was organized June 26 , 1862 , to include Washington , D . C . ; Alexandria , Virginia ; and Fort Washington , Maryland . It was a District under the Department of the Potomac . It was incorporated into the Department of the Rappahanock from April 4 , 1862 through June 26 , 1862 , when it again became an independent command . On February 2 , 1863 it merged into the Department of Washington . Commanded by Brigadier General James S . Wadsworth . Department of the Rappahannock . The Department of the Rappahannock was formed April 4 , 1862 , from the original I Corps of the Army of the Potomac , to control the area east of the Blue Ridge Mountains to the Potomac River , the Fredricksburg and Richmond Rail Road and the District of Columbia expanded to include the area between the Potomac and Patuxent Rivers . It was merged into the Army of Virginia as III Corps on June 26 , 1862 , with Major General Irwin McDowell as its commander . Defenses of Washington , D . C . . The Defenses of Washington D . C . was a short lived command , from September 2 , 1862 through February 2 , 1863 . used for the consolidation of all the defenses of the area including and surrounding Washington , D . C . Its main focus was on the maintaining of the fortifications in extending in a ring around Washington , D . C . Department of Washington . On February 2 , 1863 , the Department of Washington was re - formed to encompass the area from north of the Potomac from Piscataway Creek to Annapolis Junction ( near present - day Fort Meade ) , west to the Monocacy River , south to the Bull Run Mountains by way of Goose Creek , then east to Occoquan River . The size of it would expand throughout the war to include the entirety of the counties in the surrounding states of Maryland and Virginia . The Quartermaster Department of the Department of Washington was the largest Quartermaster Department in the Union Army . Duties as varied as building , maintenance of fortifications , supplies , road building , transportation , and ordnance testing as well as many other duties were taken over by the quartermasters of the Washington Department . Washington , D . C . also served as a transship point for supplies and materiel destined to both the Army of the Potomac and Army of the James . XXII Corps . A Corps is a grouping of two to six divisions , providing a level of the chain of command typically commanded by a Major General . Corps were first created by an Act of Congress on July 17 , 1862 , but Major General George B . McClellan had instituted them in the spring of 1862 . Before this time , the formations were known as either " Wings " or " Grand Divisions " . Most Corps came under the operational command of an Army , but the XXII Corps did not . XXII Corps was formed as a Corps under the Department of Washington on February 2 , 1863 . As was tradition , its commanders doubled as commanders of the Department of Washington . During its time , many of the regiments that were fought out arrived to reconstitute and would then be transferred back out , most of them from or to the Army of the Potomac . Battles . Mosby ' s Raids . During the time of existence of the 43rd Battalion Virginia Cavalry , better known as Mosby ' s Rangers , Mosby ' s Command , or Mosby ' s Raiders , commanded by Colonel John S . Mosby , made many forays in the area known as " Mosby ' s Confederacy " which extended from Loudoun County to Fairfax County , Virginia . Many of the raids it performed came into the area protected by XXII Corps , and many skirmishes with Brigadier General William Gamble ' s Cavalry Division , as well as various other XXII Corps units . During its reign , Mosby ' s Raiders captured Brigadier General Edwin H . Stoughton ( then commanding the 2nd Vermont Brigade ) , cut telegraph wires during Early ' s Valley Campaign and numerous raids against rail lines and supply stations . Battle of Fort Stevens . The corps took part in the defense of Washington during Jubal Early ' s Washington Raid of 1864 , playing a major role in the defense of Fort Stevens on July 11 , 1864 . Hardin ' s Division held the skirmish lines and engaged in small engagements , suffering 73 killed and wounded . The following day , Early found the works held by veteran soldiers of Major General Horatio Wright ' s VI Corps and Brevet Brigadier General William Emory ' s XIX Corps . After making a small fight , Early would withdraw , crossing back into Virginia the next day . Components of XXII Corps . Many Regiments and Brigades serving in the XXII Corps were only temporarily assigned to it . Some mainly served during times when they were reconstituting due to battle casualties , while others were trained in the vicinity of Washington before going into the field . Yet others were heavy artillery regiments assigned to the fortifications surrounding the capital . Many units , including heavy artillery regiments , left when more soldiers were needed during Grant ' s Overland Campaign and continued through the Richmond - Petersburg Campaign until the end of the war . Some units began serving before the XXII Corps was formed . Famed Brigades in XXII Corps . The California Brigade was formed by Oregon Senator and Colonel Edwin Baker to have a California presence in the Eastern Theater . After the death of Colonel Baker at the Battle of Balls Bluff , the brigade was redesignated the Philadelphia Brigade . Made up of the 1st , 2nd , 3rd , and 5th California Infantry . After redesignation as the Philadelphia Brigade , it consisted of the 69th , 71st , 72nd , and 106th Pennsylvania Infantry . The First New Jersey Brigade was a Brigade formed by the state of New Jersey while defending Washington , D . C . . This was the first brigade in the Civil War to be formed with the intention of encompassing regiments from one state . It consisted of the 1st , 2nd , 3rd , 4th , and 10th New Jersey Infantry . By the end of the war , at different it would have up to eight New Jersey regiments . The Pennsylvania Reserve Division was formed out of an overflow of volunteers over the amount requested by the Department of War . After the Secretary of War declined to accept the new units into Federal Service , they were formed , equipped and maintained by the State of Pennsylvania . During its service in Washington , D . C . , it was composed of the 3rd , 4th , and 8th Pennsylvania Reserves . Vermont gave two brigades to the defenses of Washington , D . C . The 1st Vermont Brigade , composed of the 2nd , 3rd , 4th , and 6th Vermont Infantry . It was brigaded together through the efforts of Colonel William F . " Baldy " Smith who went to his West Point classmate and friend , Major General George B . McClellan . The 2nd Vermont Brigade , composed of 12th , 13th , 14th , 15th , and 16th Vermont Infantry , all nine - month regiments , was formed October 27 , 1862 . The Iron Brigade was the only named brigade to come from varied states , the 2nd , 6th , and 7th Wisconsin Infantry , along with the 19th Indiana Infantry and was formed on October 1 , 1861 . Although at the time , it wasn ' t known by this name , simply known as 3rd Brigade , I Corps . It wouldn ' t earn the moniker for almost a year , during the Battle of South Mountain during the Antietam Campaign .