Composed mostly of men of Irish birth. It was organized at Boston, and left the State January 11, 1862. Proceeding soon after to Hilton Head, S.C., it remained in that Department until August, when it sailed for Virginia; it was then in Stevens's Division, Ninth Corps, in which command it fought at Manassas and Chantilly. In these engagements, under command of Major Cartwright, its casualties amounted to 33 killed, 188 wounded, and 13 missing; total, 234. At Antietam- then in Willcox's Division- the regiment numbered less than 200 in line, but it lost in that battle, 12 killed and 36 wounded. It was transferred, in November, 1862, to Hancock's (1st) Division, Second Corps, in which division it afterwards remained. It was placed in the Irish Brigade, and charged with it at Fredericksburg, losing 14 killed, 124 wounded, and 20 missing, out of 4,6 engaged. In May, 1864, it crossed the Rapidan with 505 officers and men--General Barlow in command of the division. At the Wilderness the regiment lost 15 killed, 86 wounded, and 14 missing. At Spotsylvania its losses were 23 killed, 79 wounded, and 8 missing; half its losses there occurred in the affair of May 18th, in which Major Andrew J. Lawlor was killed. Colonel Byrnes, an able and gallant officer, fell at Cold Harbor. The regiment was mustered out December 13, 1864; the recruits and reenlisted men remaining in the field were consolidated into a battalion of five companies which served through the rest of the war.