Convent of Churubusco. Painting by James Walker.Wikimedia Commons

While the history of Irishmen fighting in the U.S. military has been well-documented, one story of how a group of Irish rebels fought for Mexico against the United States is not widely known. The San Patricios are far more famous in Mexico than in the US.

St. Patrick’s Battalion of The Republic of Mexico remains the only organized unit of renegade American soldiers ever to fight against the United States.

According to Blogger Regular Joe, “religious bigotry” led the group to renounce allegiance to the Anglo-Saxon Protestant powers of the United States and fight on the side of Latino Catholics in the Mexican-American War, which took place from 1846-1848.

At the same time as the war between the U.S. and Mexico was raging Ireland was suffering from the Famine. The year 1847 was the worst year of the Great Hunger, and hundreds of thousands of Irish emigrated to North America every year, with many of the men ending up in the U.S. army in exchange for pay, food, and citizenship.

At the start of the Mexican War, Catholic Irish soldiers in the U.S. army were denied the right to hold religious services, reports Regular Joe. Desertion rates were high and Mexican generals, realizing the Catholic Irish could be receptive to enticements to cross lines, offered deserters land, money, the chance of promotion and the freedom to practice their religion.

Several hundred Irishmen crossed the lines and formed what became “an elite artillery battalion” under the leadership of John Patrick O’Riley. O'Riley was born in Clifden, Co. Galway and had served in the British army before emigrating and joining the U.S. army as a private. O’Riley, along with several other Irish, is believed to have defected before war was officially declared.

Regular Joe writes: “After fighting as a legion of foreigners at the Battle of Resaca de La Palma, they became St Patrick's Battalion, marching under green flags bearing the emblems of Ireland.

Flag of the San Patricios

Flag of the San Patricios

“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, where they were stationed in the the Citadel, a massive fort blocking the entrance to the city. American General Zachary Taylor wisely avoided a frontal attack on the citadel to capture the city from the flanks.

“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 fought hard and well, pouring cannon fire into the American ranks. They were instrumental in capturing some American cannon, but the Mexicans lost the battle.”

At their final battle at Churubusco, the San Patricios were split up and sent to defend the approaches to Mexico City. Defending a convent against an attack by the U.S. army on August 20, 1847, the Irish were said to have “fought like demons.”

While Mexican officers tried to raise the white flag of surrender three times, the Irish ripped it down every time, says Regular Joe. They surrendered only after they had run out of ammunition.

The city fell and the resistance ended less than a month later.

“John O'Riley was among the 85 San Patricios taken prisoner. Seventy-two of them were tried for desertion (some had defected before war was declared, others had never been in the US army at all and therefore could not be shot for desertion.)

“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).

The hanging of the San Patricios, by Sam Chamberlain. Public Domain.

The hanging of the San Patricios, by Sam Chamberlain. Public Domain.

“O’Riley, because he had crossed the lines before the declaration of war, was among those convicted of lesser offenses. These men received lashes and were branded with a D (for deserter) on their faces or hips. Becoming "marked men." O'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 still fighting for control of the castle.”

After the war, some of the surviving Irish rebels decided to stay on in Mexico, where they would settle down and raise families. Their descendants are still there today.

Although O’Riley was thought for many years to have died soon after the last battle, there is some evidence he survived and simply faded into obscurity.

The San Patricios are even now regarded as heroes in Mexico. Every September 12, Mexicans and Irish meet at the San Jacinto plaza, in San Angel to honor Los San Patricios. Flowers are placed on a memorial while bands play the anthems of both Mexico and Ireland. Names of the San Patricios are read from a list engraved in marble to which the audience responds by calling out “He died for the Fatherland!”

Read more articles from Regular Joe here.

*Originally published in April 2015.