Lamar raised, and funded out of his own pocket, the 19th Mississippi Infantry Regiment. Mott was commissioned colonel, as he had served as an officer in the war with Mexico, and Lamar was commissioned as lieutenant colonel. Lamar resigned his professorship in the university and was, on May 14, in Montgomery, offered his regiment to the Confederate War Department. On May 15, 1862, Colonel Lamar, while reviewing his regiment, fell with an attack of vertigo, which had previously disabled him; his service as a soldier was ended.