I originally posted this on the Walker thread, but since this thread is officially hijacked, I'll post it here:
SWC: Walker, a Captain in the U.S. Mounted Rifles, approached President Polk regarding the new revolver. Polk was so impressed that he ordered William Marcy, Secretary of War to purchase the pistols. Marcy in turn contacted Lt. Col. George Talbot, chief of Army Ordnance, in early December 1846 regarding procurement of Colt's pistols, for which acceptance was given on or about Dec. 7th 1946; the contract was for 1000 pistols in three month's time at a price of $25 each, to be acquired by the Army specifically for the U.S. Mounted Rifles (hence the USMR roll engraving on the cylinder). The orders were approved before Colt approached Whitney to manufacture them. More military orders followed for the "improved" holster pistols (Dragoons), and it was this that put Colt "back in business".
Though several companies of Texas Rangers acted as scouts during the war, Walker was officially a Captain in the Army at the time he collaborated with Colt on the Walker.