At Antietam the Fifteenth sustained one of the most remarkable losses of the war. It was then in Gorman's Brigade, Sedgwick's Division, and was commanded by Lieutenant-Colonel Kimball. It carried into this action 606 officers and men, of whom 318 were killed or wounded. The killed and mortally wounded numbered 108, including a company of the Andrew Sharpshooters, which had been permanently attached to the Fifteenth while at Yorktown, making eleven companies. At Gettysburg the number engaged was 239, officers and men, of whom 148 were killed or wounded--a loss of over sixty per cent. Colonel Ward, who had lost a leg at Ball's Bluff, was killed in this action.

The Fifteenth served in the First Brigade, Second Division; General Harrow commanded the brigade at Gettysburg and General Webb at the Wilderness. Entering the latter campaign with 275 men, it lost, prior to its muster-out, 14 killed, 58 wounded, and 4 missing; not including 67, who were missing or captured at Petersburg.

The Fifteenth was raised in Worcester County. It left Worcester August 8, 1861, and returned July 14, 1864, when it was mustered out, its three years term of service having expired. Its return to Worcester was marked by a grand and memorable ovation on the part of the citizens and State authorities.