The United States Southern Command (USSOUTHCOM) traces its origins to 1903 when the first U.S. Marines arrived in Panama to protect the Panama Railroad connecting the Atlantic and Pacific Oceans across the narrow waist of the Panamanian Isthmus. The Marines remained to provide security during the early construction days of the Panama Canal.
     
     In 1904, Army Colonel William C. Gorgas was sent to the Canal Zone (as it was then called) as Chief Sanitary Officer to fight yellow fever and malaria. In two years, yellow fever was eliminated from the Canal Zone. Soon after, malaria was also brought under control. With the appointment of Army Lieutenant Colonel George W Goethals to the post of chief engineer of the Isthmian Canal Commission by then President Theodore Roosevelt in 1907, the construction changed from a civilian to a military project. 
     
     In 1911, the first troops of the U.S. Army’s 10th Infantry Regiment arrived at Camp E. S. Otis, on the Pacific side of the Isthmus. They assumed primary responsibility for Canal defense. In 1914, the Marine Battalion left the Isthmus to participate in operations against Pancho Villa in Mexico. On August 14, 1914, seven years after Goethals’ arrival, the Panama Canal opened to world commerce. 
     
     The first company of coastal artillery troops arrived in 1914 and later established fortifications at each end (Atlantic and Pacific) of the Canal, with mobile forces of infantry and light artillery centrally located to support either end. By 1915, a consolidated command was designated as Headquarters, U.S. Troops, Panama Canal Zone. The command reported directly to the Army’s Eastern Department Headquarters at Fort Jay, Governor’s Island, New York. The headquarters of this newly created command was first located in the Isthmian Canal Commission building in the town of Ancon, adjacent to Panama City. It relocated in 1916 to the nearby newly designated military post of Quarry Heights, which had begun construction in 1911. 
     
     On July 1, 1917, the Panama Canal Department was activated as a geographic command of the U.S. Army. It remained as the senior Army headquarters in the region until activation of the Caribbean Defense Command on February 10, 1941. The CDC co-located at Quarry Heights, was commanded by Lieutenant General Daniel Van Voorhis, who continued to command the Panama Canal Department. 
     
      The new command eventually assumed operational responsibility over air and naval forces assigned in its area of operations. By early 1942, a Joint Operations Center had been established at Quarry Heights. In the meantime, military strength in the area was gradually rising and reached its peak in January 1943, when 68,000 personnel were defending the Panama Canal. Military strength was sharply reduced with the termination of World War II. Between 1946 and 1974, total military strength in Panama fluctuated between 6,600 and 20,300 (with the lowest force strength in 1959). From 1975 until late 1994 total military strength in Panama remained at about 10,000 personnel. 
    
     In December 1946, President Truman approved recommendations of the Joint Chiefs of Staff for a comprehensive system of military commands to put responsibility for conducting military operations of all military forces in various geographical areas, in the hands of a single commander. Thus, the principle of unified commands was established and the Caribbean Command was one of them. Although the Caribbean Command was designated by the Defense Department on November 1, 1947, it did not become fully operational until March 10, 1948, when the old Caribbean Defense Command was inactivated. 
     
     On June 6, 1963, reflecting the fact that the command had a responsibility for U.S. military operations primarily in Central and South America, rather than in the Caribbean, it was formally redesignated as the United States Southern Command. 
     
     In January 1996 and June 1997, two phases of changes to the Department of Defense Unified Command Plan (UCP) were completed. Each phase of the UCP change added territory to SOUTHCOM’s area of responsibility. The impact of the changes is significant. 
     
     The new AOR includes the Caribbean, its 13 island nations and several U.S. and European territories, the Gulf of Mexico, as well as significant portions of the Atlantic and Pacific Oceans. The 1999 update to the UCP ─ known as VISION 21 ─ also transfers responsibility of an additional portion of the Atlantic Ocean to SOUTHCOM. On 1 October 2000, USSOUTHCOM assumed responsibility of the adjacent waters in the upper quadrant above Brazil, which was presently under the responsibility of USJFCOM. The new AOR encompases 32 nations (19 in Central and South America and 13 in the Caribbean), of which 31 are democracies, and 14 U.S. and European territories covering more than 15.6 million square miles. 
     
     With the creation of the Department of Homeland Security, USSOUTHCOM Area of Responsibility (Oct 2002) experienced minor upper boundary redistribution or changes decreasing its total boundary by 1.1 square miles. (14.5 million square miles (23.2 million square kilometers.) 
     
     With the implementation of the Panama Canal Treaties (the Panama Canal Treaty of 1977 and the Treaty concerning the Permanent Neutrality and Operations of the Panama Canal), the U.S. Southern Command was relocated in Miami, Florida on 26 September 1997. 
     
     The Southern Command, which has about 3,000 permanently assigned military and civilian personnel, has the following components: United States Army South (USARSO) at Fort Buchanan, Puerto Rico; Commander U.S. Naval Forces Southern Command (COMNAVSO), at Naval Station Roosevelt Roads, Puerto Rico; U.S. Southern Air Forces (12th Air Force at Davis-Monthan Air Force Base in Arizona); U.S. Marine Forces South (MARFORSO) in Miami, Florida; and Special Operations Command at Roosevelt Roads, Puerto Rico. In addition, under the Southern Command there are the Joint Inter-Agency Task Force-East (JIATF-East) located at Naval Air Station Key West, Florida; the Joint Task Force-Guantánamo located at U.S. Naval Base Guantánamo Bay, Cuba; the Joint Southern Surveillance Reconnaissance Operations Center (JSSROC) located at Truman Annex, NAS Key West, Florida; the Joint Task Force-Bravo located in Honduras; and 26 Security Assistance Organizations (SAO) throughout the region. These SAOs are organized as Military Groups (MilGps), Military Liaison Offices (MLOs), Office of Defense Representative (ODRs), Offices of Defense Cooperation (ODCs), Office of Defense Assistance (ODCs) and Military Assistance Advisory Group (MAAGs).