Argent a bend Gules, in base an eagle close of the last gorged with a collar Or bearing a Lorraine cross of the second. On a sinister canton of the second a demi-sun Gold charged with an Aztec banner Vert garnished of the field (for the 3rd Field Artillery).
On a wreath of the colors Argent and Gules, a dolphin embowed Argent.
PROGRESSI SUNT (They Have Advanced).
The regiment was formed from the 3rd Field Artillery which is shown on the canton. The red bend denotes artillery support. The eagle with collar, one of the supporters of the arms of St. Mihiel, symbolizes the most important engagement in which the regiment participated.
The dolphin represents overseas service.
The coat of arms was originally approved for the 21st Field Artillery Regiment on 5 February 1921. It was amended to correct the blazon on 20 May 1921. It was redesignated for the 21st Field Artillery Battalion on 13 December 1940. The insignia was redesignated for the 21st Artillery Regiment on 30 August 1957. Effective 1 September 1971, the insignia was redesignated for the 21st Field Artillery Regiment.