Air-Defense Radar Museum

A non-profit veterans group of mostly U.S. Air Force veterans dedicated to preserving the memories and history of  Cold War air defense radar stations and associated control centers.

http://www.radomes.org/museum/

Civil War Fortification Study Group

Primarily study the temporary field fortifications and battle sites of the American Civil War era.

http://www.cwfsg.org

Coast Defense Study Group

Their primary purpose is to promote and encourage the study of coastal defense.  They publish the CDSG Journal and a quarterly newsletter.  The CDSG Press has reprinted a number o historical fortification manuals and can provide back issues of their journal on computer disc.

http://www.cdsg.org

Company of Military Historians

Devoted to the study and dissemination of "information on the uniforms, equipment, history and traditions of members of the Armed Forces of the United States worldwide and other nations serving in the Western Hemisphere."

http://www.military-historians.org

Society of Military History

Efforts are devoted to stimulating and advancing the study of military history.

http://www.smh-hq.org