Distinctive Unit Insignia. Description: A Silver color metal and enamel device 1 3/32 inches (2.78 cm) in height overall consisting of a shield blazoned: Gules, a pale Argent, on a chief of the last a setting sun of the first. Attached below the shield a Red scroll turned Silver inscribed "SEMPER TENTARE" in Silver letters.
         Symbolism: The shield is red and white, the Engineer Corps colors. The pale represents the Columbia River and the setting sun symbolizes that the organization is allocated to the most western states.
         Background: The distinctive unit insignia was originally approved for the 321st Engineer Regiment, Organized Reserves on 14 July 1930. It was redesignated for the 321st Engineer Battalion on 22 September 1942.

Coat of Arms.
         Blazon:
                 Shield: Gules, a pale Argent, on a chief of the last a setting sun of the first.
                 Crest: That for the regiments and separate battalions of the Army Reserve: On a wreath of the colors (Argent and Gules) the Lexington Minute Man Proper. The statue of the Minute Man, Captain John Parker (H.H. Kitson, sculptor), stands on the Common in Lexington, Massachusetts.
                 Motto: SEMPER TENTARE.
         Symbolism:
                 Shield: The shield is red and white, the Engineer Corps colors. The pale represents the Columbia River and the setting sun symbolizes that the organization is allocated to the most western states.
                 Crest: The crest is that of the United States Army Reserve.
         Background: The coat of arms was originally approved for the 321st Engineer Regiment, Organized Reserves on 11 November 1926. It was redesignated for the 321st Engineer Battalion on 22 September 1942.