On July 28, 1866, the United States Congress reorganized the regular army into five artillery, ten cavalry, and forty-five infantry regiments. Six regiments were reserved for black enlisted personnel, in partial recognition of the role black soldiers had played during the Civil War. Three years later, however, Congress consolidated the regular force, reducing the infantry regiments to twenty-five. As part of this reduction, the Thirty-eighth and Forty-first regiments, two of the units reserved for black troops and including many former slaves, were combined to form the Twenty-fourth Infantry Regiment. On November 1, 1869, Col. Ranald S. Mackenzie, previously head of the Forty-first, assumed command of the new regiment at Fort McKavett, Texas, which had been headquarters for Mackenzie's old regiment. The following year Mackenzie was transferred to the Fourth Cavalry Regiment. He was replaced in his old command by Col. Abner Doubleday, a fellow Civil War combat veteran also known for his work developing the game of baseball. Lt. Col. William R. Shafter assumed second-in-command. The Twenty-fourth helped garrison several posts in western Texas and along the Rio Grande until 1880, when the regiment was transferred to the Indian territory. There it remained until the late 1890s, when it was shifted to Fort Douglas, Utah. During its years in Texas, the Twenty-fourth Infantry, as did most frontier regiments, engaged largely in garrison duty, routine patrols, and minor skirmishing. Several companies, however, took part in Mackenzie's expedition toward the headwaters of the Freshwater Fork of the Brazos River in 1872 and Shafter's 1875 and 1876 forays into the Staked Plains. Strong contingents from the regiment also participated in Shafter's subsequent expeditions into Mexico, which were designed to interdict Indian raids into the United States. Detachments also saw action in the campaigns against Victorio. Composed entirely of black enlisted men and white officers during this period, the Twenty-fourth's soldiers encountered a good deal of racial prejudice despite their strong record in the campaigns against the Indians.
During the Spanish-American War the Twenty-fourth Infantry Regiment once again distinguished itself in the bloody engagements at El Caney and San Juan Hill. The following year it was sent to the Philippines, where the regiment participated in antiinsurgency operations until 1902. In 1916 it served in the punitive expedition against Mexico. A brief stint in Texas the following year saw part of the regiment involved in the Houston Riot of 1917. Following the outbreak of World War II in April 1942, it was the first black unit transferred overseas, to the South Pacific. The regiment was used largely as a service unit in the New Hebrides until some elements saw combat on Bougainville in March 1944. Between December 1944 and August 1945 the Twenty-fourth helped eliminate the remnants of Japanese defenders on Saipan and Tinian. Still segregated, the regiment was assigned to occupation duty in Japan following the war. It was thrown hurriedly into action in Korea in 1950, at which time the regiment came under criticism for its performance in combat and was deactivated in 1951.