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.
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.
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.