Noted for its famous commanders and high casualties, it served in the Eastern Theater, and fought in many important battles, including Antietam and Gettysburg.
[1] The Secretary of War, Simon Cameron, was a political enemy of Andrew Curtin, Pennsylvania governor, and refused to take the extra men into Federal service.
Curtin decided to retain the extra men and organized, trained, and equipped them at state expense.
The creation of the special division was approved by the Pennsylvania legislature on May 15, 1861, "for the purpose of suppressing insurrections, or to repel invasions.
The exceptions to this include the 2nd Brigade, most of which did not take part at Gettysburg, as it was assigned to the Washington, D.C., defenses,[3] and the detachment of several artillery batteries and cavalry troops to other divisions.
The division's parent formation resumed its I Corps designation just prior to the Antietam campaign when it rejoined the Army of the Potomac.