One of the oddest episodes in American military history occurred during the Mexican War. In 1846 the Mormons were beginning their epic trek West which would end with their carving a Mormon Zion out of the wilderness in what is now Utah. The Mormons, realizing they would need at least tacit Federal approval to accomplish this, sent representatives to Washington. The Polk administration asked for a quid pro quo. The Federal government would render assistance if a battalion of Mormons would enlist to fight in the Mexican War. Brigham Young readily agreed, and a battalion was raised after much cajoling by Young, due to the suspicion of most Mormons of the Federal government as a result of Federal indifference to the persecution of Mormons in Illinois and Missouri.
Along with the approximately 500 men, the Battalion was accompanied by 30 Mormon women, 23 of whom served as laundresses, and 51 children. The Mormons were mustered into the Army on July 16, 1846. They were assigned to the Army of the West under General Kearney, a tough regular. From Fort Leavenworth on August 30, 1846, the Mormon Battalion made the longest infantry march in US military history, 1900 miles to San Diego, California which they reached on January 29, 1847. The Battalion captured Tuscon, Arizona on the way to California, but saw no fighting, although the harsh climate and terrain they marched through more than made up for the absence of human adversaries.
The Battalion was discharged on July 26, 1847 in Los Angeles, and most of the men began the long trek to rejoin the Mormons in Utah. Among the men who marched in the Mormon Battalion was George Stoneman, a future governor of California. The video below at the end shows members of the battalion rejoining a Mormon wagon train after their service in the Mexican War.
The Mormon Battalion was the only religiously based unit ever to serve in the US military. Antagonism continued between the Mormons and the Federal government after the Mormons settled in Utah, breaking out into a small almost bloodless brief war in the 1850s. For many years most Mormons in the decades following the Mexican War viewed the creation of the Mormon Battalion as an unjust Federal imposition on their church. Their descendants, Mormons long ago having become part of the American mainstream, tend to look back on the Battalion with patriotic pride.
Donald R. McClarey
Paul Zummo
Almost Chosen People 
My own ancestor was a sergeant in the battallion, leaving behind his wife and seven children. At the end of the march he helped discover gold in Sutter’s Mill but left the gold behind to go back to Utah, where he helped build the transcontinental railroad and drive the golden spike. They don’t make ’em like they used to.
We stand on the shoulders of giants Adam.