During late summer 1863, much of the Union Army lay besieged in Chattanooga, Tennessee. To alleviate this situation, about 18,000 troops from the Army of the Potomac were transported to the Chattanooga area by train. The 75th Pennsylvania was among those units transferred. On September 24, the regiment received marching orders and immediately broke camp at Warrenton, Virginia. The troops marched east through the night, arriving at Warrenton Junction the following morning. They then turned north along the tracks of the Orange and Alexandria Railroad reaching Manassas at 5:00 p.m. on the afternoon of the 25th. There, the men were herded aboard railroad cars. In a complex movement that entailed several changes of trains and engines, the troops passed through Washington, D.C., Harper's Ferry, Maryland, Grafton, West Virginia, and Columbus, Ohio, before arriving in Indianapolis, Indiana. From there, they travelled south, passing through Louisville, Kentucky, and Nashville, Tennessee, before arriving in Bridgeport, Alabama, on October 2, 1863.