At the battles of Chantilly and South Mountain he commanded his regiment; and at Antietam, after one attempt to carry the bridge in front of Burnside had been made and failed, Col. Griffin was ordered to make the assault with his own regiment and the Second Maryland. The charge was gallantly made, but the approaches were difficult, the enemy's fire destructive, and the column was checked; but re-enforcements were brought up, and the bridge was carried, and the Sixth New Hampshire, with Col. Griffin at its head, was the first to plant its colors on the heights beyond. For gallantry in this action he was recommended for promotion to brigadier-general. At Fredericksburg he commanded his regiment, which again suffered severely in the assault on the heights. Soon after that battle he obtained a leave of absence, and was married to Margaret R. Lamson, of Keene, N. H., with whom he is still living, and by whom he has two sons. Early in the year 1863, the ninth corps was transferred to the department of Ohio, and Col. Griffin was placed in command of the second brigade, second division, serving in Kentucky. From there the first and second divisions were sent to aid Grant at Vicksburg; and, upon the fall of that city, Sherman moved upon Jackson, Miss., the capital of the state, driving Johnston before him. While approaching the town, Col. Griffin was at one time in command of the advanced line, consisting of three brigades, when a sharp attack was made by the enemy, at three o'clock in the morning, with a view to breaking our lines by surprise, but was repulsed with considerable loss. Returning to Kentucky, he took command of the second division, and marched over the Cumberland mountains, joining Gen. Burnside at Knoxville. Several regiments of the corps had been left in Kentucky, and Col. Griffin was sent to conduct them forward to Knoxville. Before they had started on the march, however, Kentucky itself was threatened with raids, in consequence of our defeat at Chickamauga, and Col. Griffin and his troops were retained for the defense of that state. While on that duty his regiment re-enlisted for three years, or the war; and in January, 1864, he was ordered with it to Covington, Ky., where they were remustered into the United States service, and immediately proceeded to New Hampshire on their thirty days' furlough, granted by the terms of re-enlistment.