The Saint Patrick's Battalion

Los San Patricios

John Riley
Photo by Christopher Minster

The St. Patrick's Battalion—known in Spanish as el Batallón de los San Patricios—was a Mexican army unit comprised primarily of Irish Catholics who had defected from the invading US army during the Mexican-American War. The St. Patrick's Battalion was an elite artillery unit which inflicted great damage on the Americans during the battles of Buena Vista and Churubusco. The unit was led by Irish defector John Riley. After the Battle of Churubusco, most members of the battalion were killed or captured: most of those taken prisoner were hanged and the majority of the others were branded and whipped. After the war, the unit lasted for a short time before being disbanded.

The Mexican-American War

By 1846, tensions between the USA and Mexico had reached a critical point. Mexico was enraged by the American annexation of Texas, and the USA had its eye on Mexico's sparsely populated western holdings, such as California, New Mexico, and Utah. Armies were sent to the border and it didn't take long for a series of skirmishes to flare into an all-out war. The Americans took the offensive, invading first from the north and later from the east after capturing the port of Veracruz. In September of 1847, the Americans would capture Mexico City, forcing Mexico to surrender.

Irish Catholics in the USA

Many Irish were immigrating to America at about the same time as the war, due to harsh conditions and famine in Ireland. Thousands of them joined the US army in cities like New York and Boston, hoping for some pay and US citizenship. Most of them were Catholic. The US army (and US society in general) was at that time very intolerant towards both Irish and Catholics. Irish were seen as lazy and ignorant, while Catholics were considered fools who were easily distracted by pageantry and led by a faraway pope. These prejudices made life very difficult for Irish in American society at large and particularly in the army.

In the army, the Irish were considered inferior soldiers and given dirty jobs. Chances of promotion were virtually nil, and at the beginning of the war, there was no opportunity for them to attend Catholic services (by the end of the war, there were two Catholic priests serving in the army). Instead, they were forced to attend Protestant services during which Catholicism was often vilified. Punishments for infractions such as drinking or negligence of duty were often severe. Conditions were harsh for most of the soldiers, even the non-Irish, and thousands would desert during the course of the war.

Mexican Enticements

The prospect of fighting for Mexico instead of the USA had a certain attraction for some of the men. Mexican generals learned of the plight of the Irish soldiers and actively encouraged defections. The Mexicans offered land and money for anyone who deserted and joined them and sent over fliers exhorting Irish Catholics to join them. In Mexico, Irish defectors were treated as heroes and given the opportunity for promotion denied them in the American army. Many of them felt a greater connection to Mexico: like Ireland, it was a poor Catholic nation. The allure of the church bells announcing mass must have been great for these soldiers far from home.

The St. Patrick's Battalion

Some of the men, including Riley, defected before the actual declaration of war. These men were quickly integrated into the Mexican army, where they were assigned to the "legion of foreigners." After the Battle of Resaca de la Palma, they were organized into the St. Patrick's Battalion. The unit was made up of primarily Irish Catholics, with a fair number of German Catholics as well, plus a handful of other nationalities, including some foreigners who had been living in Mexico before war broke out. They made a banner for themselves: a bright green standard with an Irish harp, under which was "Erin go Bragh" and the Mexican coat of arms with the words "Libertad por la Republica Mexicana." On the flip side of the banner was an image of St. Patrick and the words "San Patricio."

The St. Patricks first saw action as a unit at the Siege of Monterrey. Many of the defectors had artillery experience, so they were assigned as an elite artillery unit. At Monterrey, they were stationed in the Citadel, a massive fort blocking the entrance to the city. American General Zachary Taylor wisely sent his forces around the massive fortress and attacked the city from either side. Although the defenders of the fort did fire on American troops, the citadel was largely irrelevant to the defense of the city.

On February 23, 1847, Mexican General Santa Anna, hoping to wipe out Taylor's Army of Occupation, attacked the entrenched Americans at the Battle of Buena Vista south of Saltillo. The San Patricios played a prominent part in the battle. They were stationed on a plateau where the main Mexican attack took place. They fought with distinction, supporting an infantry advance and pouring cannon fire into the American ranks. They were instrumental in capturing some American cannons: one of the few pieces of good news for the Mexicans in this battle.

After Buena Vista, the Americans and Mexicans turned their attention to eastern Mexico, where General Winfield Scott had landed his troops and taken Veracruz. Scott marched on Mexico City: Mexican General Santa Anna raced out to meet him. The armies met at the Battle of Cerro Gordo. Many records have been lost about this battle, but the San Patricios were likely in one of the forward batteries which were tied up by a diversionary attack while the Americans circled around to attack the Mexicans from the rear: again the Mexican Army was forced to retreat.

The Battle of Churubusco

The Battle of Churubusco was the St. Patricks' greatest and final battle. The San Patricios were divided and sent to defend one of the approaches to Mexico City: Some were stationed at a defensive works at one end of a causeway into Mexico City: the others were in a fortified convent. When the Americans attacked on August 20, 1847, the San Patricios fought like demons. In the convent, Mexican soldiers three times tried to raise a white flag, and each time the San Patricios ripped it down. They only surrendered when they ran out of ammunition. Most of the San Patricios were either killed or captured in this battle: some escaped into Mexico City, but not enough to form a cohesive army unit. John Riley was among those captured. Less than a month later, Mexico City was taken by the Americans and the war was over.

Trials, Executions, and Aftermath

Eighty-five San Patricios were taken prisoner in all. Seventy-two of them were tried for desertion (presumably, the others had never joined the US army and therefore could not desert). These were divided into two groups and all of them were court-martialed: some at Tacubaya on August 23 and the rest at San Angel on August 26. When offered a chance to present a defense, many chose drunkenness: this was likely a ploy, as it was often a successful defense for deserters. It didn't work this time, however: all of the men were convicted. Several of the men were pardoned by General Scott for a variety of reasons, including age (one was 15) and for refusing to fight for the Mexicans. Fifty were hanged and one was shot (he had convinced the officers that he had not actually fought for the Mexican army).

Some of the men, including Riley, had defected before the official declaration of war between the two nations: this was, by definition, a much less serious offense and they could not be executed for it. These men received lashes and were branded with a D (for deserter) on their faces or hips. Riley was branded twice on the face after the first brand was "accidentally" applied upside-down.

Sixteen were hanged at San Angel on September 10, 1847. Four more were hanged the following day at Mixcoac. Thirty were hanged on September 13 in Mixcoac, within sight of the fortress of Chapultepec, where the Americans and Mexicans were battling for control of the castle. Around 9:30 a.m., as the American flag was raised over the fortress, the prisoners were hanged: it was meant to be the last thing they ever saw. One of the men hanged that day, Francis O'Connor, had both his legs amputated the day before due to his battle wounds. When the surgeon told Colonel William Harney, the officer in charge, Harney said "Bring the damned son of a bitch out! My order was to hang 30 and by God, I'll do it!"

Those San Patricios who had not been hanged were thrown in dark dungeons for the duration of the war, after which they were freed. They re-formed and existed as a unit of the Mexican army for about a year. Many of them remained in Mexico and started families: a handful of Mexicans today can trace their lineage to one of the San Patricios. Those who remained were rewarded by the Mexican government with pensions and the land that had been offered to entice them to defect. Some returned to Ireland. Most, including Riley, vanished into Mexican obscurity.

Today, the San Patricios are still a bit of a hot topic between the two nations. To Americans, they were traitors, deserters, and turncoats who defected out of laziness and then fought out of fear. They were certainly loathed in their day: in his excellent book on the subject, Michael Hogan points out that out of thousands of deserters during the war, only the San Patricios were ever punished for it (of course, they were also the only ones to take up arms against their former comrades) and that their punishment was quite harsh and cruel.

Mexicans, however, see them in a vastly different light. To Mexicans, the San Patricios were great heroes who defected because they could not stand to see the Americans bullying a smaller, weaker Catholic nation. They fought not out of fear but out of a sense of righteousness and justice. Every year, St. Patrick's Day is celebrated in Mexico, particularly in the places where the soldiers were hanged. They have received many honors from the Mexican government, including streets named after them, plaques, postage stamps issued in their honor, etc.

What's the truth? Somewhere in between, certainly. Thousands of Irish Catholics fought for America during the war: they fought well and were loyal to their adopted nation. Many of those men deserted (men of all walks of life did during that harsh conflict) but only a fraction of those deserters joined the enemy army. This lends credence to the notion that the San Patricios did so out of a sense of justice or outrage as Catholics. Some may simply have done so for recognition: they proved that they were very skilled soldiers -arguably Mexico's best unit during the war - but promotions for Irish Catholics were few and far between in America. Riley, for example, made Colonel in the Mexican army.

In 1999, a major Hollywood movie called "One Man's Hero" was made about the St. Patrick's Battalion.


  • Eisenhower, John S.D. So Far from God: the U.S. War with Mexico, 1846-1848. Norman: the University of Oklahoma Press, 1989
  • Hogan, Michael. The Irish Soldiers of Mexico. Createspace, 2011.
  • Wheelan, Joseph. Invading Mexico: America's Continental Dream and the Mexican War, 1846-1848. New York: Carroll and Graf, 2007.
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Your Citation
Minster, Christopher. "The Saint Patrick's Battalion." ThoughtCo, Aug. 26, 2020, Minster, Christopher. (2020, August 26). The Saint Patrick's Battalion. Retrieved from Minster, Christopher. "The Saint Patrick's Battalion." ThoughtCo. (accessed March 27, 2023).