Red and white are the branch colors of the Corps of Engineers and are used predominantly on the 105th Engineer Battalion Unit Crest, which was approved on 6 February 1997. According to The Institute of Heraldry, the symbolism is copied from the authorization letter of the former 105th Engineer Battalion’s coat of arms upon which this insignia is based. The trio of fleurs-delis are taken from the coat of arms of St. Quentin and represent the principal engagements in which the unit took part during World War I. The white, eradicated bend denotes that the unit participated as combat troops in breaking the Hindenburg Line, bringing the war to a swift conclusion. "Conquer The Impossible" is the unit's aspirational motto.
The 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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The 105th Engineer Battalion first saw action during World War I when it was assigned to the 30th Division (redesignated as the 30th Infantry Division after February 1942) while designated as the 105th Engineer Regiment and Train. Demobilized after the war, it was given battalion status on 7 February 1942 through the consolidation of the 2nd Battalion, 105th Engineer Regiment (an element of the 30th Division) and the Headquarters, Headquarters and Service Company, 105th Engineer Regiment (whose lineage went back to 1861) to become the 105th Engineer Battalion. It was reorganized and redesignated as the 105th Engineer Combat Battalion on 1 August 1942, and before its November 1945 inactivation it would earn a Presidential Unit Citation.
It is unclear when the Battalion was reactivated, but Army records do indicate that the Headquarters and Headquarters Company, 105th Engineer Battalion was awarded a Meritorious Unit Commendation for its service between 4 January 2010 and 3 November 2010 in support of the War on Terrorism.