The San Patricios
The Saint Patrick Battalion was formed of mostly American immigrants from Ireland by John Riley, who deserted from the British Army in Canada, fled to the United States, joined the US Army, and when war with Mexico broke out, deserted the American Army as well. In April 1846 he deserted to the Mexicans at Matamoros. He formed the battalion from fellow Irish deserters as well as those from Germany, Scotland, the Italian peninsula, and many other countries who had been in the United States Army when the war with Mexico broke out. The battalion was formed as an artillery unit, and engaged the Americans in several battles.
Desertion was a problem for both armies during the war with Mexico, though less so for the Americans than the Mexicans. The American desertion rate was just over 8%; that of the Mexicans was well over 20%. The Mexican government promised substantial rewards for American deserters coming over to their side, including land and gold, which never materialized. Instead many of the deserters found themselves taken prisoners by American troops following defeats in battle. They were enticed with religious arguments as well, with the Mexican propaganda insisting that the war was as much against their shared faith of Roman Catholicism as it was against the Mexican government.
In 1847 Santa Anna ordered the San Patricios reorganized as an infantry unit and placed under the command of a Mexican officer. Volunteers from other European countries were added to its ranks. The San Patricios fought in the battles against Winfield Scott’s army as it pounded its way into Mexico City. The San Patricios were finally defeated at the battle of Churubusco. Of the deserters who surrendered to the American troops, those determined to have left the American army following the outbreak of the war were tried for treason and executed. Forty-eight were executed by hanging, one by firing squad. Thirty were hanged at Chapultepec as the castle was taken.
In Mexico the American deserters were received as heroes, a status they have retained over the years. In the United States the army refused to admit the existence of the San Patricios as a formal unit in order to discourage further desertion from the army of occupation in Mexico. Not until 1915 did the US Army formally admit that it had covered up the existence of the battalion. By then it had become known in Mexican and American folklore, particularly among those of Irish descent. During the 1852 presidential election Winfield Scott campaigned for president, and his treatment of the battalion became an issue with Irish voters.
The motives for the San Patricios who deserted the United States Army to serve in the Mexican Army, where the pay was less, the food worse, and the leadership poor, were as varied as the men themselves. Most army deserters simply tried to go home, not wanting to serve in any army. The San Patricios instead fought well with the Mexican army until the closing days of the war. Most who survived remained in Mexico following the war, though some returned to their homelands. They were not welcome in the United States and few attempted to return there. Many lived the rest of their lives begging on the streets of Mexican towns and villages.