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.
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 form 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.