Jefferson Davis' commission for the Mexican-American War with the signature of Albert Gallatin Brown, the 14th Governor of the State of Mississippi. The commission marks an important moment in Davis's political and military careers. At signing, Davis became the colonel in charge of Mississippi's oldest National Guard unit, the First Regiment of Mississippi Volunteers, better known as the "Mississippi Rifles." It is dated June 20th, 1846 and states that it was written and signed in the state capital Jackson, Mississippi. At the time of his election to colonel, Davis was in Washington, D.C. representing the State of Mississippi in Congress. He had previously graduated from West Point and served during the Black Hawk War. In 1846, Davis resigned as Congressman to join the Mississippi volunteers. Due to Davis' insistence and political connections in Washington, his regiment was the first to be armed with official use, rifled muskets. Colonel Davis left Washington and joined his regiment near New Orleans July 21, 1846. They used their M1841"Mississippi" Rifles proficiently and fought bravely to help General Taylor successfully defeat the Mexican Army at the Battle of Monterrey in September. Of their conduct at Monterrey Davis later wrote: "I saw no exhibition of fear, no want of confidence, but on every side the men who stood around me were prompt and willing to execute my orders." On February 22-23, 1847 at a ranch called Buena Vista the Mississippi Rifles fought successfully under Davis' command. Taylor ordered the First Regiment to save the line. Davis, although injured in the foot early in the battle, led his men and engaged the enemy. By nightfall, the Mississippi Rifles turned the Mexicans back. During the war, the Mississippians lost more men then any other volunteer unit with 39 dead in combat and another 123 lost to accidents or disease. Their bravery and victory at Buena Vista made Taylor a national hero and greatly aided him in his successful campaign for the White House in 1850. Davis also won national acclaim for his tenacity and skillful command in battle. In 1847, Taylor appointed Davis as Senator for Mississippi. Though he returned severely wounded, Davis entered the Senate and shortly thereafter became chairman of the Military Affairs Committee. Six years later, President Franklin Pierce made him secretary of war.