Saturday, March 7, 2026

Irish Battalion in Mexican-American War

Men of the San Patricio Battalion

 Translation: "In memory of the Irish Soldiers of the heroic battalion of San Patricio Maritres that gave their life for the Mexican cause during the unjust North American invasion of 1847." (names) "With gratitude from Mexico to the 112 years of your sacrifice. Sept 1955

The Saint Patrick’s Battalion (San Patricios) was a group of 700+ mostly Irish immigrant soldiers who defected from the U.S. Army to fight for Mexico in the Mexican-American War (1846–1848). Driven by nativism, anti-Catholic sentiment, and better pay, they fought fiercely but were captured at the Battle of Churubusco; 50 were executed by hanging in September 1847, making it the largest mass execution in U.S. history. These men were hung in three different locations. The courts-martial were held in Mexico shortly after capture in Tacubaya and San Ángel and during the Battle of Chapultepec. The hangings were held from 10 - 13 Sep 1847

Seventy-two to eighty-five prisoners were court-martialed. Some were considered not-guilty. Fifty were hanged. Those executed below agree with the plaque above. are listed were to include those sentenced to death.

The 1847 court martial records can be found: 
  • National Archives and Records Administration (NARA) Office of the Judge Advocate General (Army), Record Group 153.
  • Be sure to check the Regular Army muster rolls for 1846–1847

Researchers can reconstruct the events from:

  • court-martial summaries
  • military orders
  • correspondence
  • newspaper accounts
  • Mexican archival sources
There are also records in the: 
  • Mexican archives (Archivo General de la Nación)
  • Published trial summaries in military histories
  • Chapultepec campaign records

Why This Post? Shameless Plug
a3Gen Publishing is readying the historical and genealogical research guidebook by Kathleen Brandt of TracingAncestors.org. Volume I, The Early Wars, is the first relief of Behind the Uniform: Every soldier has a story.

We have mentioned its upcoming release on the Hittin' the Bricks with Kathleen podcast. This guidebook covers not only how and where to research your ancestral veterans, but also facts proven using case studies and supporting documents. So much was missing from our History classes.

Volume I of Behind the Uniform: Every soldier has a story covers the French and Indian War to the Civil War (Union and Confederates).

Who were the Irishmen of the San Patricio Battalion?

The San Patricio Battalion was a group of Irish immigrant conscripts who deserted the U.S. Army in 1846 to fight on the Mexican side in the U.S. Mexican War (1846-1848). Here is a historical review of the Irish of St. Patrick's Battalion that explains why these Irishmen deserted the American side to join and serve with their Mexican "Catholic brothers."
A popular novel by Carl Kreuger, "Saint Patrick's Battalion" may also be of interest: 
Mexicans Became USA Citizens
Mexico had abolished slavery by 1829, and this war was viewed as an attempt by the U.S. to reintroduce slavery on "free" Mexican soil. It did succeed in expanding slave land by way of the annexation of Texas.
Brainerd Dispatch, 31 Jul 2018, pg. 6

Approximately 80,000 to 100,000 Mexican citizens (California and New Mexico) became "free persons" under U.S. law. This was not extended to enslaved American persons.

Embarrassment: Swept Under the Rug

U.S. Grant on the Mexican War: 
"I was bitterly opposed to the measure, and to this day regard the war, which resulted, as one of the most unjust ever waged by a stronger against a weaker nation."

“With a soldier, the flag is paramount . . . I know the struggle with my conscience during the Mexican War. I have never altogether forgiven myself for going into that. I had very strong opinions on the subject. I do not think there was ever a more wicked war than that waged by the United States on Mexico. I thought so at the time, when I was a youngster, only I had not moral courage enough to resign. I had taken an oath to serve eight years, unless sooner discharged, and I considered my supreme duty was to my flag. I had a horror of the Mexican War, and I have always believed that it was on our part most unjust.

This War ushered in the Civil War. 


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