The St. Patrick's Battalion in the Mexican-American War

To celebrate St. Patrick’s Day this year, I read several books about a group of deserters from the U.S. Army of Occupation during the Mexican-American War.  These turncoats were immigrants, primarily Catholic and mainly from Ireland, who established the St. Patrick’s Battalion[1] and fought valiantly against the Americans in five major battles. They are honored to this day as heroes in Mexico, and St. Patrick’s Day is a time when their deaths in battle and by mass execution after capture by the U.S. are memorialized.  The leader of the battalion was John Riley.  He joined the U.S. Army in 1845 in Michigan and drilled at West Point using artillery skills he had learned in his prior service in the British Army. John Riley was an Irish Catholic immigrant who soon found himself taken up in the United States' war against Mexico. 

The war culminated twenty years of tension between Mexico and the United States. It centered their dispute over Texas and the U.S. view that Manifest Destiny ordained a national goal of creating a country stretching from the Atlantic to the Pacific Ocean. The American government offered to buy California and other western territories from Mexico to achieve the latter but was rebuffed. The election of James K. Polk as president of the United States in 1844 strengthened the political faction that wanted to go to war with Mexico to annex her territory in the West. Many Americans cited the unjust nature of the war at the time, which gave rise to the first anti-war movement in our country’s history. “Civil Disobedience” was written by Henry David Thoreau as a protest to the war with Mexico causing Thoreau to refuse to pay a poll tax.  Another critical issue was slavery, and there was heightened Northern concern over the westward spread of slavery. Others were concerned with American soldiers fighting in a foreign land. For these reasons, Texas remained an independent republic for eight years (from April 21, 1836, when General Antonio Lopez de Santa Anna was defeated at the Battle of San Jacinto, until the admission of Texas into the Union in 1845).

With the annexation of Texas by the United States, President Polk sent General Zachary Taylor to lead the Army of Observation, comprised of 3,900 men, which were half the total U.S. enlisted forces.  John Riley was part of Company K, 5th U.S. Infantry.  At this point, the U.S. had 734 officers and 6,563 enlisted men. Fifty percent of these troops were made up of immigrants: 24% - Irish, 10% - German, 6% - English, and 4% West Europe-Canada. The U.S. Congress voted to fund eight additional regiments of infantry, two mounted cavalry units (dragoons), four artillery units, and administrative staff.  Congress also authorized a call for 50,000 volunteers.  As war approached, the U.S. Army increased the number of enlisted men and volunteers by 42,587 and 73,532, respectively.  The Marine Corps strength rose sharply as new units were created for the war, with Mexico going from 42 officers and 986 men before the war to 75 officers and 1,757 men in 1847.  Mexican forces, the Army of the North, numbering approximately 3,700 men under General Pedro de Ampudia, moved to the Rio Grande near Matamoros on April 12, 1846. General Mariano Arista soon replaced Ampudia.[2]

The Mexican government had ordered both Ampudia and Arista to attack the American force under General Zachary Taylor, who established an initial base of operations at Point Isabella in mid-1845 near Corpus Christi before moving to the Rio Grande opposite Matamoros in February 1846, where he established Fort Texas. Negotiations continued with the Mexican government but were not productive.[2] In the meanwhile, desertions from the U.S. Army began in earnest.  Taylor ordered sentries to shoot to kill any soldiers attempting to swim across the Rio Grande to Matamoros.  This problem plagued the army throughout the war: “Out of 40,000 regulars who saw duty during the conflict, a stunning 5,331 -- nearly thirteen percent of the ranks – deserted.”[3] Of the 5,000 Irishmen who enlisted in the regular army, one in five deserted, and many of them fought in what became the St. Patrick’s Battalion. 

Hostilities began on April 25, 1846, when Mexican forces attacked a U.S. cavalry unit, killing eleven, wounding six, and capturing 47.  This bloodshed prompted President Polk to push Congress for a declaration of war, which Congress enacted on May 13th.  Mexico reciprocated with the United States declaring war on July 2, 1846. The U.S. Army of Observation became the Army of Occupation, and the issue of desertion became increasingly important for the Polk administration. 

Propaganda leaflets from the Mexican government were distributed, highlighting the war as a campaign against Roman Catholicism by the predominantly Protestant United States. The plea was for Irish and other immigrant Catholics to protect the faith against a Protestant onslaught.  President Polk asked Georgetown College to provide two priests to act as Catholic chaplains to the Army of Occupation.  There was also an effort to curb the harsh discipline applied to immigrant soldiers.  A significant number of officers also supported Nativism, which called for discrimination against Catholic immigrants.[4]  As the U.S. began to recruit heavily for an expanded army, a full one-third of the recruits were immigrants from Ireland, Great Britain, and other countries.  The U.S. Army’s treatment of these immigrants is thought to have contributed to the high desertion levels. In this setting, John Riley deserted on April 12, 1846, and accepted a commission in the Mexican Army of the North and a monthly pay of $57, which was eight times greater than his pay in the U.S. Army.

After joining the Mexican Army, John Riley asked General Arista to serve in an artillery company, and with 48 other deserters, primarily Irish, he formed an artillery battery that saw its initial action in the bombardment of Fort Texas.  Zachary Taylor left a small force at Fort Texas (later Fort Brown and Brownsville) and took the main body down the Rio Grande to the coast and onto Point Isabell to protect his supply lines. After he accomplished that, he marched his forces back toward Matamoros to relieve the siege of the fort.

General Arista sent his main force against the American force.  He encountered Taylor and the main body of his army at Palo Alto on May 8th along the coastal road from Point Isabell to Ft. Texas.  The battle started at 2 pm and lasted until dusk.  The Mexican forces were forced to retreat and assume a defensive position at Resaca de la Palma, where a second battle occurred on May 9, 1846.  The Mexican forces were routed, and they retreated to Matamoros. After the battles, General Taylor noted the bravery of Irish soldiers but also highlighted the support provided to the Mexicans by Irish deserters.  John Riley later wrote that he had participated in the shelling of Ft. Texas, where the commanding officer, Major Brown, was wounded and died three days later. The loss of Major Brown and other American officers and enlisted men at the hands of the Irish and immigrant manned artillery caused deep hatred for these deserters.  

After the retreat of the Mexican army, Ampudia was put back in charge and marched a strengthened Army of the North of 7,300 men to Monterrey.  The American forces, 6,200 men, moved up the Rio Grande and then turned south toward Monterrey.  Taylor attacked the city on September 21, 1846, in a battle that lasted three days with heavy losses on both sides.  During the first day, the Army of Occupation lost ten percent of its total force with 400 casualties as the Mexicans fought bravely from strong defensive ramparts.  At the end of the third day, General Ampudia asked for a parley with General Taylor. To prevent more civilian deaths, Ampudia agreed to leave the city if he and his men could take their small arms and two batteries of cannon. Taylor agreed, and the Mexican army marched out of the city on September 24, 1846. John Riley and around 100 other deserters were part of the Mexican army that left Monterrey marching out between the ranks of the U.S. Army.  The San Patricios went unmolested, although the U.S. troops made their anger at the turncoats known through oaths and shouts at them.[5]  

Retreating to Saltillo and then to San Luis Potosi, the Mexican army came under the command of General Santa Anna in October 1846. Realizing the potential value of U.S. deserters, he began making a plan to entice 2,000 soldiers to come over from the American side.  “Santa Anna believed that a unit in which the deserters would serve as a body rather than scattered through the Mexican units would prove a powerful attraction for immigrants.” [6]

Based on the heroism shown at the Battle of Monterrey by John Riley and the deserters serving with him as part of the artillery company, Santa Anna approved the formation of the St. Patrick’s Battalion. During the six weeks after the Battle of Monterrey, the Army of Occupation suffered through another round of desertions.  A major in the First Regiment of Ohio Volunteers noted that more than fifty regulars crossed over to the Mexican side: “These the enemy joyfully received and speedily enrolled in their ranks, where they served with courage and fidelity, they never had exhibited in ours. Doubtless, the humblest soldier of the battalion of St. Patrick was honored with much consideration by the Mexicans.”

Many desertions were recorded in the muster rolls of the U.S. army at Monterrey.[7] Official Mexican government documents indicated that an army payroll was registered in November 1846 for the “Voluntarios Irlandeses.” Captain Francisco Rosendo Moreno was named the unit’s commander and John Riley was made responsible for training in artillery tactics and battle command. He also designed the unit battle banner.[8]

The Battle of Buena Vista took place on February 23, 1847.  Santa Anna, with 20,000 men against Zachary Taylor’s 5,000 soldiers, seemed to have broken through the left flank of the American army.  Taylor ordered Jefferson Davis’ Mississippi Rifles and the 3rd Indiana to hold the line, which they did successfully. Riley and the artillery he commanded proved deadly to the U.S. forces: “What Riley did not know yet was that his performance and that of his men at Buena Vista had awed the Mexican generals and had even earned accolades of American officers.”[9]  Zachary Taylor lost 14 percent of his army at Buena Vista.  Nevertheless, the Americans held the field and inflicted heavy losses on the Mexican army. Santa Anna retreated on February 24, 1847.

President Polk, concerned that Zachary Taylor was becoming too famous from his victories in Mexico and could become a strong political rival, ordered that Taylor turn over command of the U.S. army to Winfield Scott, who was heading to Veracruz with a naval assault force.  The navy bombarded Veracruz, and the Marines and the army took the city with little resistance.  The Battle of Cerro Gordo followed with heavy losses by both armies.  The Mexicans withdrew to the Mexico City valley. On August 20, 1847, the last major battle of the San Patricios was fought at Churubusco.  Santa Anna lost half his army, while 12 percent of the American forces were lost. The Americans prevailed and captured the surviving members of the St. Patrick’s Battalion. John Riley and the other deserters were tried, and 51 were sentenced to hanging. Riley and 15 others were whipped and branded with a “D” for deserter.

To me, the lessons from this history are: (1) political and cultural movements such as Nativism have repercussions in a multi-cultural society – we need to be conscious of the secondary effects of nationalism and anti-immigrant rhetoric; (2) the First Amendment guarantees religious freedom was, and is, important – trying to force a religion on others can create significant backlash; and (3) as citizens we have a moral obligation to oppose unjust actions by our nation’s leaders.

[1] “The Rogue’s March”, p.197

[2] During the six weeks after the Battle of Monterrey, the Army of Occupation suffered through another round of desertions.  A major in the First Regiment of Ohio Volunteers noted that more than fifty regulars crossed over to the Mexican side: “These the enemy joyfully received and speedily enrolled in their ranks, where they served with courage and fidelity, they never had exhibited in ours. Doubtless, the humblest soldier of the battalion of St. Patrick was honored with much consideration by the Mexicans.” Many desertions were recorded in the muster rolls of the U.S. army at Monterrey.

[3] “The Rogue’s March,” p. 166.

[4] “Shamrock and Sword” P. 47.

[5] John Riley created the banner of the St. Patrick’s Battalion and it was to become the most famous or infamous of the war. On September 9, 1847, the New Orleans Daily Picayune provided this description: “The banner is of green silk, and on one is a harp, surmounted by the Mexican coat of arms, with a scroll on which painted, ‘Libertad Por la República Mexicana’ – underneath the harp is the motto ‘Erin go Bragh’ (Ireland Forever), on the other side is a painting of St. Patrick and underneath is written ‘San Patricios.’

[6] “The Rogue’s March” Peter F. Stevens, p. 2.

[7] Note: It is thought that this type of prejudice could have reminded the Irish of the economic, social, religious, and military repression of the Irish by the British. The subsequent famine and poverty caused massive outmigration with many of the immigrants coming to the United States (175,000 Irish immigrants entered the United States from 1840 to 1844).

[8] “The Mexican War 1846 -1848, K. Jack Bauer, Macmillan Publishing Company, New York, N.Y. 1974.

[9] In the “Shamrock and Sword,” Robert Ryal Miller cited the failed negotiations of John Slidell with the Mexican government.  His objective was to offer payment of Mexico’s debt to the U.S. in exchange for their recognition of the Rio Grande as their border with Texas and the United States.  He was also authorized to offer $25 million to purchase California. The Mexican government refused to accept Slidell, citing the encampment of a U.S. army on Mexican soil (Texas). While Slidell was waiting to present his credentials, a coup removed the Mexican president with the new leader, Major General Mariano Paredes y Arrillaga, refusing to see Slidell and vowing to maintain Mexico’s border to the Sabine River, the Texas – Louisiana border.

Note: The St. Patrick’s Battalion (the San Patricios) consisted primarily of Catholic immigrants, a plurality of whom were Irish (39 percent), fought in five major battles.  George Ballentine, an English soldier in the U.S. army, wrote of the St. Patrick’s Battalion that they “fought like devils” and at the Battle of Churubusco just outside Mexico City, they inflicted heavy casualties on several American units and “settled old scores by seeking and killing dozens of West Point officers with the malignity of private revenge.”