In July of 1845, General Taylor’s force began moving to Texas. Most of his force embarked from New Orleans bound for Corpus Christi, Texas. The Second Dragoons were the exception, choosing to proceed over land from Fort Jessup to Corpus Christi. They made the 501-mile march in 32 days, and reported to General Taylor in fine shape, contrary to some predictions from others outside the command. In March of 1846 General Taylor was ordered to move his force to the Rio Grande River in order to repel any invasion. General Taylor’s force departed Corpus Christi to establish a base of operations at Point Isabel. The vanguard of his force, led by a squadron from the Second Dragoons and Major Ringold’s Flying Artillery, subsequently moved to establish Fort Texas along the Rio Grande River. This position was directly across from the Mexican city of Matamoras, near what is now Brownsville, Texas.
The Dragoons began an aggressive schedule of mounted patrols along the Rio Grande. Acting as the eyes and ears for General Taylor and maintaining security along the flanks, the Regiment became well acquainted with the area and some of the local ranchers. On 25 April 1846 General Taylor received word that the Mexican Army was crossing the river above and below his position. Two companies of dragoons moved to the lower crossing while Companies C and F went to reconnoiter the upper crossing. The next day one of the Company’s native guides returned to camp claiming that the units had been attacked by a large force of Mexicans near La Rosia and that “all had been either cut to pieces or captured.” The two companies of dragoons, numbering 60 men, were surrounded and ambushed by over 500 Mexican cavalry. They sustained nine dead and two wounded. Thornton was pinned to the ground when his horse was shot dead in mid-air as he cleared an eight-foot wall of chaparral in an attempt to charge through the enemy. The entire command, now under Captain William Hardee, was captured and taken to Matamoras. This battle gave President Polk the excuse he needed to invade Mexico.
During a counter-attack at Palo Alto on 8 May 1846, the Regiment was largely responsible for forcing the enemy to the east and exposing its left flank. The next day at Resaca de la Palma, General Taylor ordered Captain Charles A. May to silence a battery of Mexican cannons that had been blocking the Matamoras Road. May said, “I’m going to charge them,” as he led his squadron (Companies D and E) through the American infantry lines and into the fire from the Mexican artillery. May overwhelmed the battery and captured a Mexican general. May’s order of the day, “Remember your Regiment and follow your officers,” has become the Regiment’s motto.
Another hero of the Mexican war was Sergeant Jack Miller, whose small patrol was ambushed by a force five times its number near Monclova in November 1847. The dragoons were going for their carbines when Miller shouted: “No firing, men! If 20 dragoons can’t whip 100 Mexicans with the saber, I’ll join the Doughboys and cart a fence rail all my life.” The Dragoons charged and killed six Mexicans, wounded thirteen, and captured seventy. Casualties in Miller’s unit were limited to only one man wounded and three mounts lightly scratched.
On 29 June 1846, Colonel Twiggs, the First Colonel of the Regiment, recently promoted to Brigadier General after ten years in command, passed command of the Regiment to his successor, Colonel Harney. Harney remained in command for the duration of the Mexican War. Congress later awarded Twiggs a sword with a jeweled hilt and a gold scabbard as a tribute to his gallantry at Monterey. The Regiment’s service proved invaluable in every major campaign of the war, and it is one of perhaps two regiments in the Army to have had elements participate in every battle. The Regiment added 14 green and gray campaign streamers to the Regimental standard during the war with Mexico.