The service of the "3rd Regiment Cavalry, Maryland Volunteers" began on August 8, 1864, with the raising of three companies at Baltimore. In September and October, Companies D, E, F, and G were recruited from Confederate prisoners at Fort Delaware, most of whom had been captured at the Battle of Gettysburg, numbering approximately 450 in all. The regiment remained in garrison at Camp Schenck in Baltimore, seeking to raise more troops, assigned to the Cavalry Reserve of the Eighth Corps until officially organized on January 9, 1864. Sent by steamship to New Orleans and Madisonville, Louisiana, the 3rd Maryland Cavalry took part in the Red River Campaign, in the Atchafalaya Expedition in the first week of June 1864, and in August was dismounted to participate in the siege of Fort Morgan. Disease seriously depleted the ranks of the regiment, and in December 1864, the 3rd Maryland Cavalry consolidated into a six-company battalion. Company D became part of Company E, and Company G part of Company F, participating in the campaign to capture Mobile, Alabama in March and April 1865. The 3rd Maryland Cavalry was the only unit of "galvanized Yankees" in Federal service to actively campaign against Confederate forces. At the end of hostilities it was assigned to the Department of Mississippi and garrisoned Natchez, Mississippi, through the summer of 1865. The battalion mustered out at Vicksburg on September 7, 1865.