Organized August 14, 1862, with Captain C. W. Tilden, of the Second Maine, as its Colonel, who commanded it during its entire service. Arriving at Washington on August 21, 1862, it was ordered immediately on active duty in Maryland. The fatigue and exposure of a campaign without the customary preparatory service cost the regiment many lives, and sent large numbers to the hospital. It was assigned to Root's (1st) Brigade, Gibbon's (2d) Division, First Corps, and marched to Fredericksburg with that command. This was its first battle; but its ranks had become so reduced by the sickness, common among raw troops in active service, that only 427 were present in that action, of which it lost 27 killed, 170 wounded, and 34 missing; of the latter none returned. Another severe loss was sustained at Gettysburg. Of the 248 officers and men engaged in that battle, the casualties amounted to 9 killed, 59 wounded, and 164 captured. At the close of the fight, 2 officers and 15 men alone remained; Colonel Tilden was taken prisoner with his men. Many of the wounded died and nearly all the amputations proved fatal. In March, 1864, the division was transferred to the Fifth Corps; in June the regiment was transferred to Crawford's (3d) Division, and to Baxter's (2d) Brigade of the same corps. It fought in all the battles of the Fifth Corps in 1864-5, its hardest fighting occurring at Spotsylvania, where Major Leavitt fell, mortally wounded. Another severe fight took place at Hatcher's Run (Dabney's Mills) February 6, 1865, in which the regiment lost 3 killed, 60 wounded, and 11 missing.