On a blue four-leaf clover two crossed arrows in white, points up, superimposed thereon a red acorn fimbriated white all on a 2 3/4 inches (6.99cm) square Army Green background.
The crossed arrows are representative of the fighting power of the organization, the acorn is indicative of strength, and the four-leaf clover represents good fortune.
The shoulder sleeve insignia was originally approved for the XXI Army Corps on 3 Apr 1944. It was redesignated for the XXI U. S. Army Corps, Army Reserve on 11 Oct 1957and on 4 Nov 1957 it was amended to delete the words "Army Reserve." The insignia was amended on 28 May 1959 to change the background color from olive drab to Army Green. A distinctive unit insignia was not approved for the XXI U. S. Army Corps. (TIOH Drawing Number A-1-270)