By 1855, Congress realizing the number of mounted soldiers was not enough authorized the raising of two more regiments, the 1st Cavalry and the 2nd Cavalry. Secretary Of War Jefferson Davis had lobbied hard for two new mounted regiments and consequently appointed the majority of officers.
Among them were in the 1rst Regt., Captain George B. McClellan, (Major General, Commander, Army of the Potomac and the inventor of the famed McClellan saddle), and 2nd Lieutenant James E.B. (Jeb) Stuart, (Major General, CSA, Commander of the Confederate Cavalry Corps).
The 2nd Regt included 12 future generals: field officers Robert E. Lee (who was appointed to succeed to command in 1861), William J. Hardee, and George H. Thomas, and line officers Earl Van Dorn, Edmund Kirby Smith, George Stoneman, Kenner Garrard, William B. Royall, Nathan G. Evans, Fitzhugh Lee, and John B. Hood.
The 1st Cavalry Regiments were constituted on 3 March 1855. The 1rst was organized at Jefferson Barracks, Missouri on 26 March 1855 under the command of Colonel Edwin Voss Sumner.
The 2nd Regt. was organized at Louisville Kentucky under the command of Albert Sidney Johnston.
The 1rst Regt was, upon completion of the organization of the regiment in August 1855, assigned to Fort Leavenworth, Kansas. Its mission was two-fold; to maintain law and order in the Kansas Territory between pro and anti-slavery factions and to protect the settlers from attacks by the Cheyenne Indians. In 1857 the regiment was split with half taking up new quarters at Fort Riley, Kansas and the rest maintaining small garrisons scattered throughout the state. On 3 March 1861, Colonel Robert E. Lee assumed command of the 1st Cavalry only to resign his commission a month later to lead the Confederate States Army in the Civil War.
The 2nd organizing on 28 May 1855. A few months later, on 27 September 1855, the regiment of 750 officers and men marched west to fight in its first Indian Campaign, against the Comanche, reaching Fort Belknap, Texas, in late December.
Both Regts campaigned variously throughout the western frontier from Texas throughout the Kansas Territory engaged against primarily Comanches in the south and the Cheyenne in the north.
As early as 1854, the War Department had been wanting to redesignate all mounted regiments as cavalry and to renumber them in order of seniority. Thus in August 1861 the 1rst Dragoons became the 1rst Cavalry, the 2nd Dragoons became the 2nd Cavalry, the U.S. Mounted Rifles became the 3rd. Cavalry. As the 1st Cavalry Regiment was the fourth oldest mounted regiment in terms of active service, it was redesignated as the 4th Cavalry and the 2nd Cavalry Regiment became the 5th in August 1861.
In 1855 the two new "cavalry" regiments adopted generally the same blue wool uniforms as the three previous regiments with the exception that they were once again trimmed in yellow tape. However the 1rst and 2nd Cav. were issued a new style of hat that would be popular during the early years of the Civil War. Known as the Hardee hat apparently was named after William J. Hardee. Also in 1855 a new "forage cap" was issued often known as the McDowell cap.