The Army of the Potomac.
The Northern army was called the Army of the Potomac and was under the command of General George G. Meade.
The Army of the Potomac. George G. Meade replaced Joseph Hooker in command only days before the battle.
General Robert E. Lee commanded the Army of Northern Virginia at Gettysburg.
Every battle fought by the Army of Northern Virginia was against the Union army.
Robert E. Lee
The Confederate army that fought at the First Battle of Bull Run was called the Confederate Army of the Potomac. Later it was renamed to the Army of Northern Virginia.
Interestingly the battle was over a shoe supply at Gettysburg. But this escalated into a chance for the CSA army of Northern Virginia to destroy the USA army of the Potomac and so the battle was fought. After about 4 days of fighting though the CSA, who were winning, decided to commit military suicide by the name of Pickett's Charge, so they lost the battle.
It is called the Battle of Gettysburg.
Meade
The revolutionary army
The first name of what would become the Army of Northern Virginia was the Confederate Army of the Potomac. That was in 1861. As early 1862 came about the name was changed to the Army of Northern Virginia.
Army of Northern Virginia.