The 166th Infantry Regiment Distinctive Unit Insignia (DUI), also called a unit crest, was approved on 31 July 1926. Its white and blue colors are a testament to the unit’s rich heritage, dating to 1846: white was the Infantry color at that time, and blue did not replace it until 1903. The insignia’s most prominent element, a tri-colored rainbow, is the device of the 42nd Division in World War I, its parent organization while assigned to the 83rd Infantry Brigade. A black Maltese cross below commemorates the Regiment’s service in Puerto Rico in the Spanish-American War (also known as the War with Spain). “Follow Me” is the unit motto.
Distinctive Unit Insignias are worn by all Soldiers (except General Officers) in units that have been authorized to be issued the device. It is worn centered on the shoulder loops of the Army Green Service Uniform (AGSU) and the blue Army Service Uniform (ASU, Enlisted only) with the base of the insignia toward the outside shoulder seam. DUIs are not worn on the Dress variations of either uniform, however.
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The Regiment’s lineage begins with the organization of the 2nd Regiment, Ohio Volunteer Infantry from existing companies in South-Central Ohio, a group that was mustered into Federal service and which took part in the Buena Vista campaign in the Mexican War. By the time of the Civil War, it had been redesignated as the 3rd and 4th Regiments, Ohio Volunteer Infantry; the two units served in the Union army from 1861 to 1864 (1865 for 4th Regiment, which had been reorganized as the 4th Battalion by that time) and fought in eleven campaigns. During the War with Spain, the unit—now designated as the 4th Ohio Volunteer Infantry—was called into served and fought in Puerto Rico, earning a campaign streamer for its overseas service.
Though mustered into Federal service for Mexican Border duty in 1916, the Regiment was not part of the Mexican Expedition (also called the Punitive Expedition), but it would soon see combat after it was drafted into Federal service e on 5 August 1917 and reorganized and redesignated as the 166th Infantry. Assigned to the “Rainbow Division,” it would fight in two campaigns during World War I, the Meuse-Argonne offensive and the Battle of St. Mihiel.
The Regiment would be reorganized between the wars and was assigned to the 37th Division up until February 1942. During the war, the Regiment’s 1st Battalion served garrison duty in the Caribbean, while the 3rd Battalion was assigned to Replacement and School Command at Fort Sill, Oklahoma. None of the Regiment’s units saw combat during the war, and in fact World War I would mark the last conflict in which the Regiment saw action.
The Regiment underwent several reorganizations after the end of World War II, most consisting of changing either the number of its allotted battalions or the parent units of which they were elements; between 1963 and 1977, its 1st Battalion was reorganized from being an element of the 37th Infantry Division to the 38th Infantry Division and then the 73rd Infantry Brigade. Withdrawn from the Combat Arms Regimental System in 1989, the Regiment was consolidated with the 148th Infantry and the consolidated unit given the 148th Infantry designation and acquired the 166th’s lineage, battle honors, and military decorations.