A sawtooth line, its very shape recalling the work done by Engineers, serves as a proxy bend dexter to divide the 109th Engineer Battalion Distinctive Unit Insignia into and white and scarlet halves, colors of the Engineer Corps. In the upper right is a castle taken from the Spanish Campaign Medal to represent service in the War with Spain; the cactus stands for duty along the Mexican Border; and the fleur-de-lis denotes World War service in France. “ALLONS Y FAIRE” is French for “Let’s Go Do It.”
This Distinctive Unit Insignia was originally approved for the 109th Engineer Regiment on 23 May 1927. It was redesignated for the 109th Engineer Battalion on 2 September 1943. The insignia was amended to add a motto on 15 October 1968.
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 (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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Inactivated in August 2007 as part of the Army’s organizational transformation, the 109th Engineer Battalion recently (November 2019) was reactivated during an uncasing ceremony at its home base in Rapid City, South Dakota. Its history goes back to 1884 and the creation of the Dakota Territory Militia, and its battle honors include campaign streamers from the Philippine Insurrection, World War I, World War II, and Operation Iraqi Freedom.