In order to supply the Union troops, Pennsylvania industries turned their attention toward producing war material. The Alleghany Arsenal, Fort Pitt Works, Frankford Arsenal, and Schuylkill Arsenal produced thousands of cannons, ammunition, and clothing. Additionally, the Baldwin Locomotive Works assisted in building railroad engines that the armies used to transport troops and materials during the war; the Philadelphia navy yard allowed for warships and supply ships to harbor; and coal mines across the commonwealth helped keep these industries operating.

The most significant military operation to take place in the commonwealth occurred during the first few days of July 1863. As Confederate forces entered Pennsylvania during their invasion of the North, roughly 37,000 militiamen were called into service to help protect the commonwealth. As the Union Army of the Potomac chased after the Confederate Army of Northern Virginia, the armies collided in the small town of Gettysburg. This collision caused the largest, and perhaps the most significant, battle of the entire war. After an astounding 50,000 combined casualties during the three days of fighting, the defeated Confederate army retreated from Pennsylvania and back to Virginia. Pennsylvania did see more military action later on in the war, when a small Confederate force invaded in July 1864. While entering the town of Chambersburg, Confederate General Jubal Early demanded a ransom; when citizens were unable to meet the demand, Confederate forces burned the town’s central district.

Although the commonwealth did not see a large amount of military action, Pennsylvania was second only to New York in the number of soldiers provided to the Union with approximately 350,000 men. Pennsylvania ranked first among Northern states in the number of African American soldiers. Over 8,000 African Americans volunteered to fight for the Union. Soldiers, both black and white, the militiamen who answered the call to help protect the commonwealth, and the thousands of workers in factories, farms, and mines, all helped to shape the final outcome of this war.