In 1845, the expansionist minded President Polk easily convinced Congress to authorize the annexation of Texas, and soon approve the Oregon Treaty which divided Pacific coast Northwest along the 49th parallel. To protect the thousands of settlers moving west in the spirit of Manifest Destiny, President Polk signed the formation of “a regiment of mounted riflemen” into law on 19 May 1846.
The Mounted Riflemen, armed with the Model 1841 Mississippi rifle, would be a separate and distinct branch from the musket armed infantrymen and the carbine armed dragoons (All American cavalry at this point were technically dragoons; hussars, lancers, and cuirassiers were too limited by their battlefield roles and fell out of favor after the War of 1812). They were recruited from across the US, and formed at Jefferson Barracks, Missouri under Colonel Persifor Fraser Smith. Smith’s men rode to battle but fought on foot, and the “The Regiment of Mounted Riflemen” was charged with protecting the settlers on the Oregon Trail.
However, they wouldn’t execute that mission for several years. In early May 1846, Mexican army incursions across the Rio Grande initiated the Mexican American War, and the Regiment was called upon to participate in Gen Winfield Scott’s invasion of Mexico at Vera Cruz in 1847. They lost their horses in the transit and fought on foot for the entire campaign which was actually beneficial as it allowed them to distinguish themselves in battles, as opposed to guarding supply trains and hunting bandits.
On 20 August 1847 after the Battle of Contreras, General Scott addressed the men of the regiment, “Brave Rifles, Veterans – you have been baptized in fire and blood and come out steel. Where bloody work was to be done, “the Rifles” was the cry, and there they were…”
The Regiment of Mounted Riflemen, forever known as the Brave Rifles, would eventually be re-designated to what we know them as today: the 3rd Cavalry Regiment.