Originally designed as the War Department Library, the room was designed by Richard von Ezdorf and completed in 1887. Ezdorf selected an eclectic mix of the French Renaissance, Classical, and Gothic Revival styles. Mixing elements of these styles was very popular in the late 19th Century, and became characteristic of the high Victorian style. Finished eleven years after the State Department Library, the difference in the treatment of the ironwork and the pattern of the English Minton tile floor is evident, as well as the difference in scale.

The ornamentation within the library reflects the War Department.s military heraldry. For example, the terra cotta oak leaves in the cove ceiling represent steadfastness and civic virtue. The acorns in the same detail represent life and productivity. This decoration was once lit by gas jets, the pipes of whish are still in place. The salamanders in the lower level shelving panels suggest bravery and courage. The butterflies in the floor represent immortality. Laurel leaves on the columns may symbolize glory and victory due to Laurel-crowned heroes following Roman-era battles.

The metals in the room are cast iron, which has been treated in a variety of ways to imitate other metals. A patented treatment of the metal following the Bower-Barff process created the dark rough surfaces. The thin pressed panels were created using the Galvano-plastic process, and electroplating created copper surfaces of the fluted columns. The adjustable shelving is also cast iron.

The War Department's library collection included books, charts, maps, and photographs. Prominent among the photographs were all the photographs and their negatives taken by Matthew Brady during the Civil War, whish were acquired by the War Department in 1875 for $25,000.00 when financial difficulties forced Brady to sell them. The U.S. Signal Corps became responsible for the library in 1894, and the War Department occupied the space until 1938 when they vacated the building.

Between 1938 and 1970, the library was used for storage. In 1970, the library was renovated for use as a conference room. The renovation installed carpeting over the tilled floor, a dropped acoustical ceiling reduced the height of the room to one story, and gold-colored drapes hid the perimeter metal paneled walls from view.