The regiment left Maine for Washington, D.C., on April 18, 1864, and was attached to the 2nd Brigade, 2nd Division, IX Corps of the Army of the Potomac, in which it served for the remainder of the war.
The regiment fought again at Spotsylvania Court House on May 12, again taking heavy casualties: 12 killed, 75 wounded and 108 missing in action.
At the Battle of the Crater on July 30, 1864, it was the first regiment than charged the Confederate position and took heavily casualties in the ensuing failed assault.
The regiment remained in reserve from February 11, 1865, until the early morning of April 2, when it was chosen to provide the initial storming party of three companies for the assault on Fort Mahone, Petersburg.
It participated in the occupation of Petersburg and spent the remainder of the campaign gathering and escorting Confederate prisoners to the rear.