Here's a piece from my "Today In Irish History" file about the San Patricios.

20 Aug 1847 The US Army of invasion overwhelmed the defending Mexican army and captured the Churubusco Convent. Seventy-two members of the "Battalia San Patricio" were captured, including their leader, Col. Frank Reilly. The San Patricios were predominantly Irish-born catholics who had crossed over from the American army. Less than a month after their capture, thirty of the San Patricios were hung by General Winfield Scott as they were made to watch the storming of Chapultepec castle by US forces. (Christenson, 1998 @ 203-4) U.S. President Ulysses S. Grant, then a Lieutenant, was with the invading army and referred to the battle in his Personal Memoir as "the severest battle fought in the Valley of Mexico." He went on to remark that "some of the [Mexican] gunners that stood their ground were deserters [the San Partricio's] from General Taylor's army on the Rio Grande."