The following is taken from New York in the War of the Rebellion, 3rd ed. Frederick Phisterer. Albany: J. B. Lyon Company, 1912.

May 29, 1863, Col. Robert M. Richardson received authority to reorganize the I2th N. Y. Volunteer Infantry, discharged by reason of expiration of its term of service, as a regiment of cavalry. The regiment was organized at Syracuse for a service of three years, and the companies were mustered in the service of the United States at Syracuse, A, B and C August 8; D, F and G August 26; E August 15; H September 5; K October 15; at the Cavalry Depot, D. C., Company I November 30, 1863; and at Elmira, Companies L and M January 20, and 24, 1864, respectively.

The companies were recruited principally: A at Syracuse and Oneida; B at Syracuse and Oswego; C at Syracuse, Canandaigua, Geneva, Palmyra and Potter; D at Syracuse; E and F at Syracuse, Batavia, Lockport and Rochester; G at Syracuse, Ithaca and Caroline; H at Syracuse, Lysander, Ithaca and Otisco; I at Syracuse, Oswego, Lansing and Ithaca; K at Syracuse, Ithaca, Utica and Lansing; L at Elmira, Bloomingburgh, Goshen, Cuba, Chester, Port Jervis, Westfield, Dunkirk, Deerpark and Jamestown; and M at Elmira, Westmoreland, Newburgh, Ellenburgh, Whitestown, Oriskany, Vernon, Kingston and Utica.

Companies A, B, C and E left the State September 2, 1863; D, F and G later in September; H and K in October; I in November, 1863; and L and M in January, 1864; and the regiment served at Camp Stoneman, and in 22d Corps, Department of Washington, Va., from September, 1863; in the 2d Brigade, 1st Division, Cavalry of West Virginia, from January, 1864; at Cumberland, Md., Remount Camp, from August 25 to October, 1864, and while there was assigned to the 2d Brigade, 3d Division, Cavalry Corps, Army of the Potomac; in the Army of the Shenandoah from October, 1864; with the Army of the Potomac from March, 1865.

June 17, 1865, the regiment, commanded by Col. John J. Coppinger, was consolidated with the 6th N. Y. Volunteer Cavalry, the consolidated force receiving the designation, 2d Provisional Regiment, N. Y. Volunteer Cavalry, the 15th Regiment being consolidated into four companies, which became Companies F, G, H and K of the new organization.

During its service, the regiment lost by death, killed in action, 3 officers, 18 enlisted men; of wounds received in action, 19 enlisted men; of disease and other causes, 4 officers, 126 enlisted men; total, 7 officers, 163 enlisted men; aggregate, 170; of whom 44 enlisted men died in the hands of the enemy.

The following is taken from The Union army: a history of military affairs in the loyal states, 1861-65 -- records of the regiments in the Union army -- cyclopedia of battles -- memoirs of commanders and soldiers, Volume II: New York, Maryland, West Virginia and Ohio. Madison, WI: Federal Pub. Co., 1908.

Fifteenth Cavalry.—Cols., Robert M. Richardson, John P. Coppinger; Lieut. -Cols., Augustus J. Root, Henry Roessle; Majs., Joseph H. Wood, Henry Roessle, Jeflferson C. Bigelow, Robert H. S. Hyde, Michael Auer, George M. Elicot. In the spring of 1863 Col. Richardson was authorized to reorganize the 12th N. Y. infantry, discharged on account of the expiration of its term of service, as a regiment of cavalry. The regiment was organized at Syracuse, for three years' service, and was there mustered in between Aug. 8, 1863, and Jan. 24, 1864, Cos. L and M being mustered in at Elmira, and Co. I at the cavalry depot, D. C. A large proportion of the men were from Syracuse, and the others were recruited in Onondaga, Ontario, Oneida, Chautauqua, Cattaraugus, Genesee, Tompkins and Erie counties. The regiment was consolidated with the 6th N. Y. cavalry on June 17, 1865, the new organization being designated the 2nd provisional regiment, N. Y. volunteer cavalry. The regiment left the state by detachments from Sept. 2, 1863, to Jan., 1864, and was assigned to the 22nd corps. Department of Washington, until Jan.. 1864, when it was assigned to the 2nd brigade, 1st division, cavalry of West Virginia, with which it was engaged at Hillsboro, Strasburg, Upperville, Franklin, Romney, Moorefield, Luraj-^ gap, Mt. Jackson, New Market, Front Royal, Newtown, Woodstock, Piedmont, Staunton, Waynesboro, Lexington, New London, Diamond hill, Lynchburg (where its losses aggregated 32 men), Salem, Bunker Hill, Bolivar heights, Leetown, Martinsburg, Snicker's gap, Ashby's gap, Kernstown, Winchester and Charlestown. It was then ordered to the remount camp, Cumberland, Md., remaining there from Aug. 25 to Oct., 1864. While there it was assigned to the 2nd brigade, 3d cavalry division. Army of the Potomac, but soon after joined the Army of the Shenandoah and was engaged at Green Springs, Va., with a loss of 46 killed, wounded and missing; at Lacy Springs, with a loss of 29; and near Harrisonburg on the same day, without loss. As a part of the Army of the Potomac it took part in the Appomattox campaign, being engaged at Dinwiddie Court House, Five Forks, Petersburg, Deep creek, Jetersville, Sailor's creek and Appomattox Station. In this closing campaign its losses aggregated 51 killed, wounded and missing. The brave Lieut. -Col. Root was among the killed, losing his life at Appomattox Court House, April 8, 1865, just as the final scenes of the war were being enacted. The only other officers lost in action by the regiment were ist Lieut. William P. Shearer, killed in a skirmish with guerrillas; and 2nd Lieut. Lorenzo W. Hatch, killed at Green Springs. The regiment lost during service 3 officers and 120 men killed or mortally wounded; 4 officers and 126 men died of disease, accidents, in prison, etc., a total of 7 officers and 163 enlisted men, of whom 44 died as prisoners.