John Riley & St Patrick’s Battalion Part 1: The Irish Heroes of the Mexican-American War

Words by Stephen Canavan

The creation and existence of the St Patrick’s Battalion (El Batallón de los San Patricios) during the Mexican-American War of 1846-48 is perhaps the most controversial and shocking story to emerge from that bitter war. A crack artillery unit of principally, but not exclusively, Irish and German Catholics, their story would end in glorious defeat and shocking mass executions. It would be covered up by the US military for more than 70 years.

Led by Galway born Irishman John Riley, the battalion would prove during the war to be the US Army’s toughest opponents. Riley, a tall black-haired man, was born in Clifden in County Galway, and first entered the United States in 1843 in Michigan, having served for a time in the British Army. Perhaps through boredom or the belief that his old military skills would be welcomed; Riley joined the US Army in Michigan in 1845.

Riley soon found that the US Army, especially it’s officer class, to be deeply racist, anti-Catholic, and anti immigrant, reflecting the opinions and prejudices held by a great many American citizens at the time.


A bust of John Riley in San Jacinto Square, Mexico City.
A bust of John Riley in San Jacinto Square, Mexico City.


They were the so called ‘Nativists’, who viewed all immigrants, but especially Catholic immigrants, as the enemy of native born Protestant Americans. Riley saw that these beliefs were reflected in the disproportionate number of his countrymen or co-religionists being punished for the most trivial offences, with punishments like being ‘Bucked and Gagged’ or ‘Riding the Horse’ especially popular. He also found that despite his previous military experience, his skills as an artillerymen were being either deliberately ignored or consciously neglected, much to his personal indignation.

Despite these resentments, by March 1846, Riley was marching towards the Rio Grande, serving in the mostly Irish Catholic and German ranks of Company K, the 5th US Infantry Regiment, under the command of General Zachary Taylor.

They camped threateningly in the imposing Fort Brown, across the river facing the Mexican city of Matamoros. War between the United States and Mexico seemed inevitable, for the issue of Texan independence and it’s annexation into the Union had not been satisfactorily resolved, despite the Texan Army defeating Mexican forces at San Jacinto and the Treaties of Velasco in 1836. Mexico still refused to recognise Texas as either an independent nation or state.

When new President James Polk signed the legislation formalising the ‘Lone Star State’ as a part of the Union on December 29th 1845, the wheels for war with Mexico were set in motion. The United States, under the complex and expansionist ideological banner of ‘Manifest Destiny’, would soon be marching to war.

An anti-Catholic cartoon from the 1840s
An anti-Catholic cartoon from the 1840s

John Riley’s Break with the US Army 

Conditions on the Rio Grande only seemed to increase the hostility of the officers towards the Irish and the Catholics in Riley’s regiment. Officers such as Braxton Bragg and Thomas Sherman were notorious ‘Nativists’ and anti-Catholics, and this bigotry, combined with his professional frustration and unease at being part of a Protestant army invading a Catholic nation, increased Riley’s sense of alienation from the US army. He deserted on 12 April 1846.

Writing later he said:

Listening only to the advice of my conscience for the liberty of a people which had war brought on them by most unjust aggression…I separated myself from the American forces.

He would not be the last Irishman to do so.

Drafted into a Mexican regiment known as the Legion de Extranjeros (Legion of Foreigners), Riley had soon organised a company of 48 Irishmen, known as the ‘Voluntarios Irlandeses’.

This fledgling battalion, now named the Batallón de San Patricio, would fight for the first time on the Mexican side at the Battle of Monterrey on 20 September 1846. Manning the field guns, they repelled at least three concerted assaults on their positions by US troops.

Despite their artillery prowess, the Mexican forces were defeated and when the Mexican General Ampudia surrendered the city to Taylor’s forces, Riley was forced to march past his shocked and disgusted former colleagues, who hurled much abuse at seeing their former comrades in the uniform of their enemy. Despite this defeat, Santa Anna turned over his heaviest guns to Riley’s regiment – his 24 and 16 pounders – and Riley, alongside fellow Irishman and deserter, Captain Patrick Dalton, immediately began drilling his gun crews in the revolutionary tactics of the US Army.

A modern reconstruction of the flag of the St Patrick's Batallion
A modern reconstruction of the flag of the St Patrick’s Batallion

Birth of the St Patrick’s Battalion

At Buena Vista – on 23 February 1847 – the banner of the San Patrick’s Battalion was first flown in battle. The San Patricio – numbering approximately 80 men – were assigned the high ground, a position not only of trust but of honour on the battlefield, and given the three heaviest field guns – the 16 pounders.

Bombarding the enemy, they were quick to fire down upon the US troops, before decimating Washington’s 4th Artillery, D Battery position. Members of the San Patricio then raced from behind their gun positions to help capture two US Cannons – the first time American artillery pieces had been lost to an enemy on a field of battle.

Enraged by their actions US Commander Zachary Taylor, memorably ordered a squadron of the 1st Dragoons to “Take that damned battery,” but they were repelled with typical ferocity and were forced to retreat. US Officer’s Braxton Bragg crack artillery unit halted the charge though – raining shot and canister down upon on the Mexican infantry – crippling their advance – and he and his battery became locked in a deadly battle with Riley’s San Patricio’s.

As both sides poured deadly shot and canister into the others position’s, Riley’s regiment lost one third of its men in the deadly duel of metal, until they were forced to retreat again, much to the relief of the equally shattered Americans. Mexican General Francisco Mejia concluding that the San Patricio were “worthy of the most consummate praise because the men fought with daring bravery.”

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  • The Rogue’s March: John Riley and the St Patrick Battalion 1846-48 by Peter F Stevens
  • The Irish Soldiers of Mexico by Michael Hogan
  • Wherever Green is Worn by Tim Pat Coogan
  • Shamrock and Sword: The St Patrick’s Battalion in the US – Mexican War by Robert Ryal Miller