About 32 years of age at the time of the battle, Silas A. Miller grew up in Orangetown, Rockland County New York. In the 1860 Census he is listed as a railroad conductor, and lived with his wife Margaret and their three young girls, Ellen, Emma, and Anna. Miller enlisted in Company A of the 12th U.S. on August 17, 1861, and received a promotion to Sergeant Major. He was then promoted to 2nd Lieutenant, and eventually 1st Lieutenant.
Assigned to the First Brigade of the Second Division, 5th Corps, the 12th U.S. arrived on the southern portion of the battlefield on the evening of July 2nd commanded by Captain Thomas S. Dunn. Initially, the brigade formed along the Wheatfield Road, just north of Little Round Top, and in support of the Second Brigade of the division. Soon the division advanced across Plum Run Valley to northern extension of Houck's Ridge at the eastern boundary of the Wheatfield. Here Lieutenant Miller and his command could witness some of the action taking place in the Wheatfield, as Caldwell's division of the 2nd Corps reached the apex of its attack and began to fall back in confusion. While not actively engaged in its front, the 12th probably received harassing fire from skirmishers of Benning's brigade posted near Devil's Den.
As federal positions in the Wheatfield collapsed, the Second Brigade of the division would advance in a hopeless attempt to stem the tide. When the Second Brigade also collapsed, it was left to the 12th U.S. and the other members of Colonel Hannibal Day's First Brigade to conduct a fighting retreat in the face of surging Confederate pressure, which the men conducted in good order.
Sadly, during this action Lieutenant Miller was killed. In August, the following article appeared in Lieutenant Miller's hometown paper:
Rockland County Journal
15 August 1863
Lieut. S. A. Miller.
Among the slain heroes at Gettysburg was Lieut. S. A. Miller, son of Silas Miller, at Piermont, and long and favorably known to the people of our county. About 18 months ago he enlisted as a private in the 12th Infantry U.S.A., and conducted himself with such coolness and bravery in the different actions in which he participated, that on the 19th of last April he received a Lieutenant's commission in the same regiment. At South Mountain he was taken prisoner and carried to Richmond, where after an imprisonment of six weeks he was paroled and exchanged. He was in the battle of Fredericksburg and at Chancellorsville, and closed his career as a soldier at Gettysburg, where he was shot in the region of the heart, about 6 o'clock p.m., on the 2d of July. His body was recovered and given a decent burial. We have seen letters from young Miller's brother officers which speak of his bravery and noble qualities in the highest terms. The war has claimed no nobler victim, nor brought low a more shining mark than this gallant soldier of freedom. His memory will be forever embalmed in the grateful remembrance of the nation for which he died.