Organized at Boston in May, 1861, and left the State on June 15th. It was placed in Richardson's Brigade, Tyler's Division, in which command it fought at First Bull Run. In October it was transferred to Hooker's Division, and ordered on duty in Lower Maryland, where it remained until it moved to Yorktown. It served during 1862 in Grover's (1st) Brigade, Hooker's (2d) Division, Third Corps. In the affair on the picket line -- June 25, 1862 -- known as Oak Grove, it was prominently engaged, losing 9 killed and 55 wounded. At Glendale it lost 89 in killed and wounded, Major Charles P. Chandler being among the killed. At Chancellorsville, the regiment is credited with having fired the volley which cost the great Confederate leader, General Jackson, his life. Its casualties in that battle were 9 killed, 46 wounded, and 40 missing. At Gettysburg, under Lt.-Colonel Baldwin, the regiment encountered its greatest loss, its casualties on that field amounting to 16 killed, 83 wounded, and 21 missing. In March, 1864, the division was transferred, becoming the Fourth Division of the Second Corps, with General Gershom Mort in command. In this new command the regiment fought at the Wilderness and Spotsylvania, evincing the same heroic bearing which had helped on other fields to make the old Third Corps so illustrious. The order for muster-out came May 20, 1864, while the men were in line at Spotsylvania. The recruits and reenlisted men were tranferred to the Eleventh Massachusetts.