Peter McGrath was born in Ireland, and his family later immigrated to the United States. He enlisted in the Regiment of Mounted Rifles on September 11, 1851. He served in the regiment in New Mexico Territory for the next ten years, as a private, corporal, sergeant and finally first sergeant of Company I. He was commended for his conduct during an expedition against the Navajo Indians in October 1858.
McGrath was one of the original appointees as an officer of the newly-authorized 3rd U.S. Cavalry. He was appointed a second lieutenant in the regiment on May 14, 1861. He never joined his regiment, however. Like all of the officers appointed to the regiment from New Mexico save one, McGrath never left the territory. Trained officers were in short supply, and McGrath was kept busy training and leading volunteers over the next several months.
Peter McGrath was promoted to first lieutenant, 6th U.S. Cavalry on October 24, 1861. This is interesting, since he’s listed on the regiment’s muster rolls as a second lieutenant assigned to Company A whose whereabouts are listed as unknown until February 1862.
On March 9, 1862, Lieutenant McGrath was assigned to a light battery composed of two 12-pound howitzers and two 6-pound guns commanded by Captain John F. Ritter of the 15th U.S. Infantry.
McGrath’s battery fought in the action at Pigeon’s Ranch, or Apache Canyon, New Mexico Territory, on March 28, 1862. Lieutenant McGrath was mortally wounded during the action, and died of his wounds on May 1, 1862.
Heitman, Francis B. Historical Register and Dictionary of the United States Army (Washington: Government Printing Office, 1903), page 667.
Henry, Guy V. Military Record of Army and Civilian Appointments in the United States Army, Volume II (New York: D. Van Nostrand Publishing, 1873), pg 143.
Official Records of the War of the Rebellion, as noted within text.
Muster Rolls, 6th U.S. Cavalry, NARA, M744
Official Records of the War of the Rebellion, Series I, Volume 9, pgs 539-540.