On May 3, 1861, about a month after Fort Sumter, President Abraham Lincoln called for the formation of some regular army regiments. One of these was the 15th Infantry Regiment. It fought with the armies in the west, participating in major battles such as Shiloh, Chickamauga, and in Sherman's March to the Sea.
A few years after World War I, this unit was assigned, in order, to the Philippine Division, American Forces in China, and was relieved from China in 1938. Two years later, it was assigned to the 3rd Division. In 1957, it was relieved from that division, and organized as a parent unit in the Combat Arms Regimental System, and remains in that "position" today.
This unit fought in various campaigns, including: