By all appearances, the U.S. Army in 1846 was unprepared for the demands of waging a major war on foreign soil. In the four years since the end of the Second Seminole War, the army had been used almost exclusively for purposes of frontier defense. U.S. Army forts of the Jacksonian period typically held one or two companies (less than 100 men). Serving in small, remote outposts scattered across the western frontier, few officers and enlisted men had ever trained in regimental and brigade-sized formations, which would be required during the war with Mexico.
Officially, the U.S. army in 1846 had an authorized strength of 8,613 officers and men, composed of fourteen regiments: eight infantry, four artillery (used primarily for coastal defense), and two regiments of dragoons. In an effort to economize, the troop strength of an army company had recently been cut from 100 to forty-two enlisted men – thereby reducing the maximum size of the army to 7,883 enlisted men. In fact, the actual strength of the army was considerably smaller—approximately 5,300. The bureaucracy that administered the nation’s military establishment was similarly understaffed. William H. Marcy, appointed to head the War Department in 1845, would undertake the management of the nation’s first foreign conflict with a staff that numbered only nine clerks and two messengers.
The average infantry regiment on the eve of the war with Mexico had twenty-eight officers and 433 men on its rolls present for duty. The Third Infantry Regiment may serve as a typical example. While stationed at Corpus Christi, its January 1846 roster listed the regimental strength at forty officers and 471 enlisted men, for a total present and absent strength of 511. Twenty-two officers, sixty-four sergeants and corporals, eighteen musicians (buglers, drummers, and fifers), thirteen band members, and 262 privates were available for duty. The regiment listed two officers and forty-six enlisted men on the sick list, five officers and sixteen enlisted men on detached service, four officers and two non-commissioned officers on furlough, and nineteen enlisted men under arrest. The ten-company unit averaged twenty-six privates, twenty less than the authorized strength of forty-six.
In the years leading up to the war with Mexico, the army suffered from a lack of field leadership. With no retirement system in place, unfit and infirm officers often remained on the rolls. Indeed, only one-third of the majors, lieutenant colonels, and colonels actually served with their regiments in Mexico. A typical case was Colonel James B Many, commander of the Third Infantry. Commissioned in 1798, he had held command of the Third Regiment since 1834. Many had been on leave for several years because of age and infirmity, and command in Mexico devolved to the regiment’s lieutenant colonel, Ethan Allen Hitchcock. Not surprisingly, the limited opportunities for promotion caused resentment among younger officers, who advanced only through resignation or upon the death of a senior officer.
Despite its lack of large-scale battlefield experience, the U.S. Army could draw upon the technical experience of its highly skilled lower-grade officers, many of whom were graduates of the military academy at West Point. Established at the turn of the century, West Point had emerged after the War of 1812 as the nation’s premier engineering school, graduating forty commissioned officers each year. More than 700 served in the war with Mexico, three-quarters of the regular army’s officer corps. West Point graduates dominated the more technical branches of the army, such as artillery, engineers, and topographical corps. The war would provide valuable training for West Pointers such as Robert E. Lee, George McClellan, P.T. Beauregard, and many others who would rise to prominence in the Civil War.
Enlisted recruits typically hailed from the cities of the northeast. While the army preferred rural, native-born Americans, the majority of recruits were laborers and newly-arrived immigrants. Foreigners comprised a significant number of the enlisted men, drawn into the army by economic circumstances. As many as two thirds of army regulars had emigrated from Germany, Ireland, or England.
Although the War Department ordered the production of percussion-cap muskets during the war with Mexico, at the outset of the conflict the predominant infantry weapon was the flintlock smoothbore musket. Based on a French design, the musket had changed little since the American Revolution. Weighing ten pounds and just under five feet long--to which was attached a sixteen-inch long socket bayonet--it fired a .69 caliber ball and had effective range of approximately 100 yards. Though inaccurate by modern standards, the weapon served its purpose in an era in which military tactics relied on massed firepower.
Each artillery regiment had one company trained as "flying artillery." Equipped with Model 1841 bronze 6 and 12-pounders, this horse-drawn artillery had tremendous mobility on the battlefield. The 6-pounder was capable of throwing a solid six-pound shot 1,700 yards; the 12-pounder could throw a twelve-pound projectile 1,800 yards. The flying artillery companies would prove decisive in the earliest battles of the war, at Palo Alto and Resaca de la Palma.
With the declaration of war in May 1846, Congress authorized the call-up of fifty thousand volunteers, to be raised under the auspices of the state militias for a twelve-month period. The War Department issued the call to the following states: Alabama, Kentucky, Illinois, Indiana, Ohio, Mississippi, and Tennessee. The first of these troops would not arrive in Mexico until June and July. Congress also took steps to increase the strength of the regular army, raising the number of privates in a company to one hundred, and creating an engineer company and a new regiment, the U.S. Mounted Rifles. Nine months later, Congress passed the Ten Regiment Bill, authorizing the creation of ten regiments, approximately 11,000 men, to serve for the duration of the war.
Returns from Regular Army Infantry Regiments, June 1821–December 1916. NARA microfilm publication M665, rolls 1–244, 297–300 of 300. Records of the Adjutant General's Office, 1780's–1917, Record Group 94, and Records of United States Regular Army Mobile Units, 1821–1942, Record Group 391. National Archives and Records Administration, Washington, D.C.
Coffman, Edward M. The Old Army: A Portrait of the American Army in Peacetime, 1784-1898. New York: Oxford University Press, 1986.
Henry, William Seaton. Campaign Sketches of the War with Mexico. New York: Harper & Brothers, 1847.
Stewart, Richard W., General Editor. American Military History Volume 1 The United States Army and the Forging of a Nation, 1775–1917. Washington, D.C.: Center of Military History, United States Army, 2009.
Watson, Samuel J. "Manifest Destiny and Military Professionalism: Junior U.S. Army Officers’ Attitudes Toward War with Mexico, 1844-1846." The Southwestern Historical Quarterly, Vol. 99, No. 4 (April, 1996): 467-498.
Winders, Richard Bruce. Mr. Polk’s Army: The American Military Experience in the Mexican War. College Station, Texas: Texas A&M University Press, 1997.