Yankees
It went by the Federal Army, Northern Army, U.S. Army, and the National Army, but the first two are most correct.
Army of the Potomac
Army of the Potomac
It was called The Army of The Potomac.
Confederate army was the name. They were also called Rebels too.
The Red Army
The Union army (or armies)
ARMY OF THE POTOMAC was the major Union Army in the eastern theater of the American Civil War
Every battle fought by the Army of Northern Virginia was against the Union army.
There were at times several Union armies operating in the Eastern Theater of the US Civil War. The main one was the Army of the Potomac. Other Union armies in the east were the Army of the James, and the Army of Virginia.
the Union
Red Army.