Historians often refer to the Mexican-American War (1846-1848) as the forgotten war since it was quickly overshadowed by the discovery of gold in California, which occurred just as the peace treaty was signed and the United States took possession of the former Mexican province. But the conflict dramatically changed the relationship between the U.S. and Mexico in ways that still reverberate.
The St. Patrick’s Battalion became an artillery force manned by primarily recently immigrated foreigners that fought directly against the same American soldiers they had mustered in and trained with.
Among the many unique ramifications of the American aggression against Mexico is that it was the only time that U.S. troops deserted and formed their own military unit within the enemy’s army. The St. Patrick’s Battalion became an artillery force manned by primarily recently immigrated foreigners that fought directly against the same American soldiers they had mustered in and trained with.
Despite a lack of combat experience, U.S. artillery units were considered among the best in the world at the time, known for their proficiency at rapid deployment and firing of their heavy weapons. The crippling tactic was known as flying artillery. The Irish battalion’s cannon and howitzers, however, supplied by Mexico, were inferior to the Americans in both range and explosive power. But the men fighting in the St. Patrick’s Battalion proved themselves skilled, formidable opponents.
Irish and German Catholic defectors were inspired to desert because of abuse and discrimination by American Protestant officers who denied the recruits the right to hold religious services, among other abuses and indignities. The bigotry was encouraged by the Nativist movement, a political policy and cultural attitude that was anti-Catholic and anti-immigrant and particularly strong in the U.S. Army at the time. Although there were a variety of nationalities among the men who choose to fight for Mexico, the Irish renegades in particular decided that they could not fight against Mexican soldiers who were also Catholic and defending their homeland, much like the Irish were against the British back home.
The leader of St. Patrick’s Battalion was Irish immigrant John Patrick Riley, a strapping, red-headed, Irish-born former sergeant major in the British Army. In September 1845, Riley joined Company K of the 5th U.S. Infantry. His new commander, Capt. Moses Merrill, was impressed with the new recruit. He recognized a kindred soul in Riley, noting that he was, “a master of arms, a well-groomed, genial, well-spoken, restless man of action.” Merrill was correct, Riley was an intelligent and highly capable soldier. However, due to discrimination and mistreatment of Irish enlistees in the American army, he and fellow Irishman Patrick Dalton, another British army vet, deserted Company K in the spring of 1846, just before Congress declared war on Mexico.
Many of the early deserters were Irish. Between 30 and 40 abandoned their posts for Mexico prior to the outbreak of hostilities after they decided it was immoral to kill Mexican soldiers trying to defend their country. These men would become part of a fighting unit that included their countrymen and other Europeans who were legal residents in Mexico to form what they initially called the Foreign Legion. Because this first phase of resistance to the American invasion was heavily dominated by Irishmen, Mexicans called the unit Colorados (Redheads).
Riley named his fighting force the Saint Patrick’s Battalion — in Spanish that translated into San Patricios. Riley also had a distinctive banner created for his unit. Composed of green silk, it had the image of St. Patrick embroidered in silver on one side, with a shamrock and a harp on the other. Later in the war, as the U.S. Army was approaching Mexico City for the ultimate battle for the country’s capital, the San Patricios artillery unit would be joined by a handful of Americans residing there, as well as by other European-born civilians, including Irish, Germans, Poles and even some Englishmen. These disparate individuals joined Riley’s battalion when they felt that their adopted homeland, lifestyle and families were threatened by the “Yankee invasion.”
The Americans had superior field artillery and small arms, but were hampered by long, logistically challenged supply lines far from the U.S., a lack of horses and mules to transport food, medicine and ammunition, susceptibility to numerous tropical diseases in the lowlands, as well as issues with desertion and a general lack of loyalty by its volunteer militias. Many volunteers simply abandoned the conflict and returned home as soon as their one-year enlistment was up. The challenges frustrated U.S. military commanders beyond reason, but despite the apparent edge held by Mexican forces, the spirited Americans were victorious in every meaningful engagement, although often with significant losses on both sides.
Over the course of the war, the two countries fought a series of intense skirmishes as U.S. forces pushed their way toward Mexico City. American naval squadrons established blockades on Mexico’s Pacific and Gulf of Mexico coasts to control ports and offload military materiel, including men, draft animals and weaponry. The Mexican infantry —the country had no navy — had the advantages of home terrain, choice of where to fortify resistance points, numerical superiority in the field and the mobility of highly trained, horse-mounted regiments that proved lethal with guns and lances in close combat.
The last major and by far bloodiest battle of the war occurred on Aug. 20, 1847, at a well-fortified Franciscan monastery just a few miles outside Mexico City. The compound was called the Convent of Santa Maria de Los Angeles at Churubusco, an Aztec word meaning “the place of the war god.” Although the artillery skills of the San Patricios had been a serious thorn in the side of the Americans in previous altercations, it was during the fight for Churubusco where the unit displayed exceptional bravery and lethality against their former comrades-in-arms. Their actions that day elevated the St. Patrick’s Battalion into national hero status in Mexico, where they are still honored today with monuments and celebrations. The battle would be the most hard-fought of the war, an epic clash dubbed Bloody Friday.
The Mexican army had barricaded the bridge over the Churubusco River with breastworks behind which they positioned cannons, mortars and riflemen. In the monastery itself, members of the San Patricios watched from the narrow windows embedded in the adobe structure’s 12-foot high walls. Directly in front of the Churubusco Monastery, John Riley’s men had constructed a fieldwork that protected their four 8-pound cannons. As Riley and the Mexican troops readied their positions, they watched thousands of fellow soldiers fleeing up the road past them. They had a pretty good idea what was chasing them.
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