My mother’s side of the family is Irish and, a million years ago, I attended St. Patrick’s grammar school here in New York City. So, for me, St. Patrick’s Day usually involved a corned beef and cabbage meal and a day off from school. (Today, I’m a vegan and the only thing Catholic about me is my past.)

Over time, March 17 became an exercise in avoiding the tens of thousands who chose to make a drunken spectacle of themselves or following the annual struggle being waged by gay men and women seeking to participate in the parade. (I never understood why they chose that battle-it’s like disabled people fighting for access ramps to McDonald’s.)

Despite all of this, I’ve finally discovered something worthwhile to commemorate on March 17: St. Patrick’s Battalion.

It was during the buildup to the Mexican-American War (1846-8) that scores of immigrant Irishmen joined the army for the $7 a month. “The U.S. anti-immigrant press of the time caricatured the Irish with simian features, portraying then as unintelligent and drunk and charging that they were seditiously loyal to the pope,” Anne-Marie O’Connor wrote in the Los Angeles Times in 1997. “But cheap Irish labor was welcome. Irish maids became as familiar as Latin American nannies are today.”

Harsh treatment did not end after the Irishmen enlisted in the armed forces. “Anglo soldiers often harassed them, beat them up,” said Robert Ryal Miller, author of Shamrock and Sword.

After President James Polk incited hostilities by sending U.S. troops into disputed territory, many of those Irish soldiers found themselves heading west to fight a war of conquest. The American army at that time, says Howard Zinn, was made up of “volunteers, not conscripts, lured by money and opportunity for social advancement via promotion in the armed forces.” Half were recent immigrants and, as Zinn reminds us, “their patriotism was not very strong.”

“Many of the Irish were also Catholic,” explained Rodolfo Acuña, author of Occupied America. “They resented the treatment of Catholic priests and nuns by the invading Protestants.”

“This is a story about assimilation,” historian Peter F. Stevens added. “A lot of these guys deserted because of the anti-Catholic, anti-foreigner movement.”

One such deserter was John Riley, an Irishman from Galway who swam across the Rio Grande after asking permission to go to Mass. “As the U.S. Army marched through Mexico’s northern deserts, others followed, and Riley became captain of a 200-member rogue column in the Mexican army,” explained O`Connor. “At San Luis Potosi, convent nuns presented them the hand-stitched banner that foreshadowed their eventual romanticization.”

A wartime newspaper correspondent from New Orleans described the banner as made of “green silk, and on one side is a harp, surmounted by the Mexican coat of arms, with a scroll on which is painted, Libertad para la República Mexicana. Underneath the harp is the motto Erin go Bragh (Ireland for Ever). On the other side is painting…made to represent St. Patrick, in his left hand a key and in his right a crook or staff resting upon a serpent.”

The group was unofficially known as the “Irish Volunteers” but Mexicans often referred to the redheaded and ruddy-complexioned men as the “Red Guards.” Formally, the unit was called the “San Patricio Company,” a title that evolved into the more familiar “St. Patrick’s Battalion.”

In five major battles, the San Patricios earned a reputation for bravery that peaked on August 20, 1847 at Churubusco where, over the course of three hours, 60 percent of the San Patricios were killed or captured by a numerically superior American army. One of the prisoners was Brevet Major John Riley.

“At their court-martial,” O’Conner stated, “most San Patricios said they had been forced to desert by the Mexicans, or had too much to drink.”

“They needed an excuse. They couldn’t say Å’I hated the United States,’ so they said they weren’t responsible,” said Miller. In some cases‹including Riley‹this defense was effective. While 50 San Patricios were sentenced to death, five others were pardoned and 15 others received a reduced sentence.

Riley himself was given 50 lashes and was hot-iron branded with a two-inch letter “D” for deserter. The San Patricios who faced the gallows were hanged in their Mexican uniforms and buried in graves dug by Riley and the other branded prisoners.

The war was over and in the name of historical cleansing, the legend of St. Patrick’s Battalion was essentially forgotten north of the border (except for the San Patricios column that marches in the San Francisco St. Patrick’s Day parade each year). The same cannot be said for Mexico where there is even a San Patricios public school.

“In 1997,” O’Connor reported, “Mexican President Ernesto Zedillo commemorated the 150th anniversary of the execution of the San Patricios at a ceremony in Mexico City’s San Jacinto Plaza, where the first of 50 hangings were staged. Irish President Mary Robinson was host of a celebration in Dublin, three days before handing over her post. Both countries issued commemorative postage stamps.” A plaque bearing those 50 names still hangs in San Jacinto Plaza.

Zedillo called the desertions “an act of conscience” and said the men “listened to the voice of justice, dignity and honor, and joined Mexican patriots who faced an aggression that lacked any justification.”

In honor of all who have faced an aggression that lacked any justification, I say Happy St. Patrick’s Day.

Mickey Z. (Michael Zezima) can be reached at mzx2@earthlink.net.