 A fraction of the regiment consisted of three-year enlistees, who formed the three-company 10th Maine Infantry Battalion (Cos. A, B, and D) upon the discharge of the two-year enlistees on April 26, 1863.The 10th Maine Battalion served as headquarters guard for the XII Corps at the Battle of Chancellorsville and as part of the Army of the Potomac's provost guard at the Battle of Gettysburg.The 10th Maine Battalion was detached from the XII Corps at Tullahoma, Tennessee, on February 29, 1864, to be amalgamated with the 29th Maine Infantry.