Originally approved on 27 September 1954, the 391st Engineer Battalion Distinctive Unit Insignia—more commonly referred to as a “unit crest” or "DUI" by Soldiers—was amended nearly forty years later in order to change the motto on 18 April 1994, followed by a second amendment to alter the description of the insignia on 31 May 1994.
The insignia’s scarlet shield containing a silver (white) saltire, or “x” shape, incorporate the two branch colors of the Corps of Engineers; they are also the reverse colors of the Florida state flag (scarlet saltire upon white background). A blue disc superimposed over the saltire’s intersection simulates a lake as an allusion to the organization’s former location in Lakeland, Florida, while the saltire also points to a brace used in Engineering construction; the two crosses of the saltire are also reflect the two battle honors afforded the unit for World War II service.
The sea lion on the disc is adapted from the Philippine coat of arms (it is also used on myriad government seals, flags, and documents in the Philippines) and is employed here as a reference to the Philippine Presidential Unit Citation the unit earned in World War II. “Build And Destroy,” the unit’s motto, bluntly describes the two main tasks facing Engineer: The creation of facilities and infrastructure for friendly and Allied units while destroying those of the enemy.
Extensive guidance on wear of the DUI is found in DA Pamphlet 670-1, Section 21-22, "Distinctive unit insignia" and 21–3(d) and (e), "Beret" and "Garrison Cap," respectively.
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Constituted on 5 May 1942 in the Army of the United States as 1st Battalion, 52nd Engineers, 391st Engineer Battalion became the 1st Battalion, 52d Engineer Combat Regiment just three months later. During the two campaigns it took part in in the Pacific Theater, it would serve under the designation of 52nd Engineer Combat Battalion, earning the Philippine Presidential Unit Citation (alluded to on its DUI), as well as an Arrowhead device denoting its participation in an assault landing during the Western Pacific campaign.
Inactivated following the end of the war, it would be redesignated as the 391st Engineer Combat Battalion and allotted to the Organized Reserves on 27 June 1947 and then receive its current designation on 12 February 1953, by which time the Organized Reserves had become the Army Reserve. Though called into active military service at home stations from October 1961 to August 1962, the organization would not be deployed into to support military operations in a hostile zone until 2005.
While serving in Afghanistan during that 2005 callup, the Battalion—less Company A—earned a Meritorious Unit Commendation for building hundreds of kilometers of roads and carried out road clearance operations. And for its part, Company A’s extraordinary heroism in actions against an armed enemy between 7 July 2005 to 1 September 2005 while attached to the 864th Engineer Battalion was recognized with a Valorous Unit Award issued in April 2008.
As of Autumn 2023, the 391st Engineer Battalion is a subordinate unit of the 926th Engineer Brigade, 412th Theater Engineer Command, U.S. Army Reserve. It is headquartered at Greenville, South Carolina.