Also known as a unit crest or DUI, 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.
Full guidance on wear of the DUI is found in DA Pamphlet 670-1,
Section 21-22, "Distinctive unit insignia."♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦
The 21st Engineer Battalion Distinctive Unit Insignia was first approved for the 5th Engineer Regiment on 23 May 1928. In November 1944 it was redesignated for the 1277th Engineer Combat Battalion, followed by another redesignation—to 21st Engineer Combat Battalion in August 1951—that gave the unit its numerical designation for the first time. Three years later, it was insignia was given its current designation for the 21st Engineer Battalion.
Like so many Engineer Battalions, the 21st Engineer Battalion can trace its origins all the way to 1861 and the Engineers and Pontoniers of the Union Army, represented here by the crossed oars and anchor image that was used during the Civil War. Yellow and black, the colors used for lower two-thirds of the insignia, were the uniform facings of the Engineer Corps.
The upper third, or chief, commemorates the organization’s WWI service in France, with the red field and white bend representing the Lorraine district; in the center of the bend is the shoulder device of the 7th Division under which the unit served in the Great War. Lastly, the crest recalls the Battalion’s service in Santiago during the War with Spain and during the Philippien Insurrection.
Assigned to the 3rd Brigade Combat Team, 101st Airborne Division, the 21st Engineer Battalion is stationed at Fort Campbell, Kentucky and is now designated as the 21st Brigade Engineer Battalion.