This site provides some information and links related to U.S. Army insignia – their history, illustrations, references and data that may be useful for researchers and collectors.
William K. Emerson has has researched, written about, and collected US Army insignia for over 40 years. He retired from the army with 20 years of service including two tours in Vietnam.
His books include:
Encyclopedia of United States Army Insignia and Uniforms
Marksmanship in the U. S. Army
United States Army Badges, 1921-2006
U.S. Army Soldiers and Their Chevrons
Chevrons: Illustrated History and Catalog of U.S. Army Insignia
Smithsonian Institution Press, 1983 (Out of Print)