The Regiment of Mounted Riflemen was authorized by an act of Congress in 1846 and brought into existence a new organization in the American Army: a regiment of riflemen, mounted for greater mobility than the infantry, and equipped with percussion rifles to provide greater range and accuracy than the muskets of the infantry or the dragoon's smooth bore carbines.

The Regiment participated in the Mexican War in 1847, distinguishing itself in six campaigns. Its participation there was climaxed by the bloody battle of Chapultepec. At the end of the Mexican War, The Regiment returned to Jefferson Barracks, Missouri, and marched to the Oregon Territory to accomplish the mission for which it had originally been organized.

TACSOP_Accolade.jpgAfter the outbreak of the Civil War in 1861, the Regiment of Mounted Riflemen found itself fighting Confederate Texans as well as Indians and in August of that year the Regiment was redesignated as the 3d United States Cavalry Regiment. Between October 1863 and March 1864, the Regiment fought in Tennessee, Mississippi, Alabama, and North Carolina as part of the advance guard of Sherman's Army. During the Spanish-American War, the 3d Cavalry Regiment participated in the attacks on San Juan and Kettle Hills. After the war, the Regiment was ordered to the Philippines to assist in quelling the Insurrection there. It fought 62 engagements between October 1899 and 1902. With the onset of World War I, the Regiment was transferred to Europe. Arriving in France in November 1917, the Regiment operated three remount depots for the duration of the war.