The Armory was added to the National Register of Historic Places in October, 1998. The complete application is available via the link below, and contains detailed historic information on the structure and use over time.
National Register of Historic Places application

Significance
According to the National Register of Historic Places and the Idaho State Historical Society, the structure is architecturally significant. It was designed by the prominent Idaho architectural firm Tourtellotte & Hummel and represents an excellent example of the firm’s Depression-era design work and the Art Deco modern movement. This WPA project reflects the period’s focus on utility and economical construction techniques, and is counted as the most important of Tourtellotte & Hummel’s major commissions during the New Deal era.

The Armory is also historically significant; it represents the culmination of state and local efforts (spanning nearly three decades) to professionalize and expand Idaho’s National Guard during the early 20th century. When dedicated in the summer of 1937, the building became the state’s largest and best-equipped armory; it remained in active use by the Idaho National Guard through the 1970s. A second floor was added to the front of the structure in 1956 to complete the original Tourtellotte & Hummel design.

As mentioned elsewhere, historic designation in itself does not offer protection, although the City and many local residents have so far indicated a desire to preserve the building’s original exterior.

Read the entire National Register application for yourself to see what conditions had to be met for the structure to acheive historic status.

You can also view scans of the original Tourtelotte and Hummel elevation drawings of the Armory via the following links (we’re looking for the original files and will relink to them soon):

1993 Warranty Deed showing transfer to City of Boise.
Armory Deed