Sorefingers, Los San Patricios were real!
Look at the data and websites posted in thread 25561 about Los San Patricios. The desertions were from the US Army in the Mexican War. Their leader was Capt. John Riley. He escaped hanging but was branded. His history is documented on both Mexican and Irish websites.
Songs San Patricios

See the songs about them in this thread. John Riley is taught about in Mexican schools. I believe one of the songs about him is in the DT.