In 1920 a French military aviation mission opened a flying training school. The 'Cuerpo de Aviacion Militar de Guatemala' was established in 1929 – with pioneer pilots Jacinto Rodríguez Díaz and Miguel Garcia Granados Solís, among others – and started to expand in 1934. The outbreak of World War II hindered any further expansion until 1942, when Guatemala started to receive lend-lease military assistance. Guatemala signed the Inter-American Treaty of Reciprocal Assistance in 1947 at Rio, Brazil. The air force was renamed the Fuerza Aerea Guatemalteca (FAG) in 1948. In the 1960s, the strike aircraft and basic interceptor used was the F-51 Mustang, supplied from surplus US stocks. The first jet aircraft to enter service was the Lockheed T-33 trainer to fight the growing insurgency; the US supplied four jets in 1963, two in 1964 and two more in 1965. In 1965, the US also supplied four armed Sikorsky UH-19B helicopters, the first military helicopters in Central America. In 1967 the FAG acquired five Bell UH-1B and UH-1D helicopters from the US to reinforce its helicopter force. In 1971 the FAG received eight Cessna A-37 Dragonfly fighter-bombers, a Vietnam-proven light attack jet. Seven more A-37s were supplied in 1974 and 1975.