A Silver color metal and enamel device 1 1/4 inches (3.18 cm) in height overall consisting of a shield blazoned: Gules, between a hammer and a saw saltirewise and a pick and a shovel in like position, a railroad track paleways throughout, all Argent. Attached above the shield from a wreath Argent and Gules an oak tree issuant from a split rock Proper. Attached below the shield a Silver scroll inscribed "EXPECT ANYTHING" in Red letters.
The shield is red with the charges thereon in silver (white), the colors of the Corps of Engineers. The railroad track alludes to the World War I service of the organization as railway engineers, while the hammer, hand-saw, pick and shovel represent the present assignment of the organization as general service. The oak tree issuant from a split rock alludes to the organization's service at Verdun and Meuse-Argonne Offensive.
The distinctive unit insignia was originally approved for the 21st Engineer Regiment (General Service) on 9 May 1940. It was amended to change the designation to the 21st Engineer Regiment (Aviation) on 17 July 1940.