Also known as a unit crest or DUI, a Distinctive Unit Insignia is 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 (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.
Enlisted personnel wear the insignia centered on a shoulder loop by placing it an equal distance from the outside shoulder seam to the outside edge of the shoulder-loop button. Officers (except Generals) wearing grade insignia on the shoulder loops center the DUI by placing it an equal distance between the inside edge of the grade insignia and the outside edge of the button.
Full guidance on wear of the DUI is found in DA Pamphlet 670-1, Section 21-22, "Distinctive unit insignia" and 21–3(d) and (e), "Beret" and "Garrison Cap," respectively.
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The Distinctive Unit Insignia the 123rd Armor Regiment, Kentucky Armor National Guard was originally approved for the 149th Infantry Regiment on 27 October 1925. It was amended less than a year later to correct the blazon (heraldic term referring to the formal description of an emblem or design), and in January 1956 it was redesignated for the 241st Tank Battalion. It was redesignated for the 123rd Armor Regiment on 23 September 1960 and was subsequently amended to change the symbolism on 2 October 1969.
Blue is used for the shield portion of the insignia to reflect the unit’s heritage that began with the organization in 1846 of the 2nd Kentucky Volunteer Infantry Regiment. Civil War service is signified by the white saltire from the flag of the Confederacy (but with the red portion now blue), and service in the Mexican War at the Battle of Buena Vista is denoted by the cactus and snake taken from the Mexican flag. Ermine in the chief (upper one third of the shield) represents World War service in Europe and is from the coats of arms of Nantes and Brittany. The unit motto, ESTO PERTUA, is a Latin phrase meaning “May It Live Forever.”