In 1846, the only religiously based unit to ever serve in United States military history included more than 500 volunteers from The Church of Jesus Christ of Latter-day Saints during the Mexican-American War. The group was known as the “Mormon Battalion.”
The battalion’s service (including a 2,000-mile march from Iowa to San Diego—one of the longest military marches in history) helped secure critical territory and aid westward expansion, though it came at great cost for the Latter-day Saints: during this time, members of the Church were fleeing persecution and violent mobs and enduring great hardship and sacrifice on their westward trek to the Great Salt Lake.
Nevertheless, when President James K. Polk appealed to the Church for men to fill the ranks of the United States army, more than 500 men accompanied by 80 women and children stepped forward to support their country in what proved to be a difficult military mission.
The Church acknowledges that military service may be necessary or beneficial to honoring and upholding the law of one’s country (Article of Faith 1:12). While Latter-day Saints believe they are to “renounce war and proclaim peace,” they also believe that it is a worthy duty to serve their country by protecting their family and neighbors, their “homes and their liberties, their wives and their children … their rites of worship and their church.” Latter-day Saints share a commitment to both peace and freedom, and as such, “support the defense of liberty wherever it is in jeopardy.”
The Church of Jesus Christ of Latter-day Saints supports and prays for those who dedicate their lives to defending freedom and peace and who honorably serve their countries. Many Latter-day Saint men and women around the world have and are enlisted in military service, whether as chaplains, scientists, medics, soldiers, and so on.
In some places, the mission service that young Mormon men and women offer to the Church (between the ages of 18 to 25) may conflict with military service. However, some choose to and are able to do both.
The Church offers a pre-military orientation for those who choose to enlist, helping servicemen and women learn how to fulfill their commitment to both their military and religious service while in the armed forces. The Church also has a Military Relations program that helps those enlisted receive support from Mormon congregations or, in their absence, receive approval from the military chaplain or commanding officer to organize service member groups.
 D&C 98:16.
 Alma 43:45-46, as quoted by former President Gordon B. Hinckley, “War and Peace,” Ensign,May 2003.
 Hinckley, “War and Peace.”
 Church Handbook, 13: Military Relations. See also http://www.lds.org/callings/military-relations