A Silver color metal and enamel device 1 1/8 inches (2.86 cm) in height overall consisting of a shield blazoned: Gules, a bundle of five arrows, point to base, one in pale and four in saltire surmounted by a yoke (from the arms of Puerto Rico) in chief Argent. Attached below the shield a Silver shield inscribed SEDULITATE in Red letters.
Scarlet and white are the colors of the Corps of Engineers. The arrows and the yoke are taken from the arms of Puerto Rico and are symbolic of that locality. The motto translates to By Diligence.
The distinctive unit insignia was originally approved for the 78th Engineer (Combat) (Corps) on 28 November 1942. It was redesignated for the 78th Engineer Combat Battalion on 31 August 1943. The insignia was redesignated for the 78th Engineer Battalion on 15 November 1956.