Lest we forget

  The St Patrick's Battalion were Irish who fought for the Mexican side against the United States in the Mexico-American War of 1846-48. 

 Contrary to the Articles of War, which stipulated that the penalty for desertion and/or defecting to the enemy during a time of war was death by firing squad, regardless of the circumstances members of the Saint Patrick's Battalion were executed by hanging as criminals.

 Although more than 9,000 U.S. soldiers deserted the army during the Mexican–American War, only the San Patricios who unlike almost all other deserters had also fought against the United States were punished by hanging.

Executions for treason took place at three separate locations on three separate dates; 16 were executed on 10 September 1847 at San Ángel, four were executed the following day at the village of Mixcoac on 11 September, and 30 were hanged at Chapultepec on 13 September.

https://en.wikipedia.org/wiki/Saint_Patrick%27s_Battalion