The Army of the Potomac (Union) was organized on July 26, 1861 under the command of Maj. Gen. George B. McClellan and served in the Eastern Theater. It was later commanded by Maj. Gens. Ambrose Burnside, Joseph Hooker, and George Meade. (Wiki)
See also: https://en.wikipedia.org/wiki/Army_of_the_Potomac
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