"Under Article I, Section 8 of the U.S. Constitution, Congress has the power to raise and support armies; provide and maintain a navy; and provide for organizing and disciplining their members. Under this authority, Congress has enacted the Uniform Code of Military Justice (UCMJ), which is the code of military criminal laws applicable to all U.S. military members worldwide. The President implemented the UCMJ through the Manual for Courts-Martial (MCM), which was initially prescribed by Executive Order 12473 (April 13, 1984). The MCM contains the Rules for Courts-Martial (RCM), the Military Rules of Evidence (MRE), and the UCMJ. The MCM covers almost all aspects of military law. Military courts are not considered Article III courts, but instead are established pursuant to Article I of the Constitution and, as a result, are of limited jurisdiction."
CRS In Focus, IF10504
Federation of American Scientists: http://www.fas.org/sgp/crs/index.html