Shield
Or, an anchor debruised by two oars in saltire Sable; a chief Gules, on a bend Argent the insignia of the 7th Division Proper (a Black hour glass on a Red disc).
Crest
On a wreath of the colors Or and Sable, a five-bastioned fort Or and thereon a crescent Gules.
Motto
FORESEE AND PROVIDE.
Shield
This unit was organized in 1917 by expanding companies C and D of the 2nd Engineers. The original components of the 2nd date back to 1861 and the 5th is not a descendent of the older regiment but is a part of it under a new name and so actually dates its historical record from 1861. The old elements were a part of the Army of the Potomac and the crossed oars and anchor is the old badge of the Engineers and Pontoniers. The colors yellow and black were each at times the facings of the Corps. The chief indicates the 5th's participation in World War I, the red field and the white bend representing Lorraine. On the bend is the shoulder device of the old Division.
Crest
The crest alludes to the old organization's service in the Santiago campaign and the Philippine Insurrection.
The coat of arms was originally approved for the 5th Engineer Regiment on 20 January 1922. It was amended to correct the wording in the crest on 16 January 1928. It was amended by the addition of a motto on 3 April 1936. It was redesignated for the 1277th Engineer Combat Battalion on 10 November 1944. The insignia was redesignated for the 21st Engineer Combat Battalion on 14 August 1951. It was redesignated for the 21st Engineer Battalion on 13 August 1954.