In United States military doctrine, unconventional warfare (abbreviated UW) is one of the core activities of irregular warfare. Unconventional warfare is essentially support provided by the military to a foreign insurgency or resistance. The legal definition of UW is: U.S. Department of Defense UW mission UW was the first mission assigned to United States Army Special Forces when they were formed in 1952; they now have additional missions, including foreign internal defense (FID). In the United States, "special forces" refers specifically to the United States Army Special Forces (SF), as opposed to the usage in most other countries, where "special forces" refers to the range of unit types that the U.S. calls "special operations forces" controlled by the United States Special Operations Command (USSOCOM). SF units are tasked with seven primary missions: unconventional warfare (United States Department of Defense doctrine) (UW) foreign internal defense (FID) special reconnaissance (SR) direct action (DA) counter-terrorism (CT) counter-proliferation (CP) psychological operations (United States) (PSYOP) information operations (IO) SF may be given other missions including warfare and support, combat search and rescue (CSAR), security assistance, peacekeeping, humanitarian assistance, humanitarian demining and counter-drug operations; other USSOCOM units or other U.S. government activities may be the specialists in these secondary areas. The UW mission assumes that U.S. forces will work with troops in another country and possibly with other allies and is always multinational. Depending on the particular situation, their role may vary from pure training to leading a joint force in combat. Over more than fifty years, roles and missions have continued to evolve, based on the history of operations. History The idea of UW came from Second World War resistance movements assisted by U.S. personnel, especially against the Empire of Japan's invasion of the Philippines as well as numerous European national resistance against the invasion by Nazi Germany. The main strength of these movements came not from U.S., but local personnel. U.S. "behind the lines" units such as Merrill's Marauders, in modern doctrine, were not conducting UW but DA and SR. The idea extended to resistance against an expected Soviet invasion of Europe following World Rarely, however, did the U.S. create a guerrilla force. Far more often, the U.S. supported an existing national organization. World War II A variety of organizations, including United States personnel, conducted UW missions. Many of the operations in the European Theater of Operations (ETO) were multinational, such as Jedburgh teams,