Saint Patrick's Battalion

The Saint Patrick's Battalion (Spanish: Batallón de San Patricio), later reorganized as the Foreign Legion of Patricios, was a Mexican Army unit which fought against the United States in the Mexican–American War. Consisting of several hundred mostly Irish and other Catholic European expatriates and immigrants, including numerous men who had deserted or defected from the United States Army, the battalion was formed and led by Irishman John Riley.

Source: Wikipedia — Saint Patrick's Battalion (CC BY-SA 4.0)