 The Japanese occupation of Indochina that year, the first step toward invasion of the rest of Southeast Asia, created an opportunity for patriotic Vietnamese.The so-called "men in black" were a 10,000 member guerrilla force that operated with the Việt Minh.He oversaw many successful military actions against the Vichy France and Japanese occupation of Vietnam during World War II, supported closely yet clandestinely by the United States Office of Strategic Services and later against the French bid to reoccupy the country (1946–1954).