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The United States Army in the Eastern Theater

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April 1861 • to May >

Commanded by Major General Winfield Scott

Department of Washington (established 4/9)
Lt. Colonel Charles F. Smith (4/9-4/28)
Colonel Joseph K. F. Mansfield (after 4/28)
Consisting of the District of Columbia (including Alexandria County, Virginia), and Maryland as far as Bladensburg.

Department of Pennsylvania (established 4/19)
Major General Robert Patterson
Consisting of Pennsylvania, Delaware, and Maryland not in the Departments of Washington or Annapolis.

Department of Annapolis (established 4/27)
Brigadier General Benjamin F. Butler
Consisting of Maryland between Annapolis, Baltimore and Washington.

Department of the East (Pre-war)
Major General John E. Wool
Consisting of all of the United States east of the Mississippi not in other departments.