The Peace Treaty of Paris of 1947 placed severe restrictions on all of the Italian armed forces, but the establishment of NATO in 1949 with Italy as a founding member brought about the necessity for the modernization of all of the Italian armed forces, including the Italian Air Force. American military aid sent by the Mutual Defense Assistance Program brought about the introduction of American-made P-47 Thunderbolt and P-51 Mustang propeller-driven fighter planes. In 1952, the Italian Air Force was granted jet fighters for the first time, American F-84G Thunderjets and F-86D Sabres, together with over 200 licence-built British de Havilland Vampires; these were followed by F-84F fighters and C-119 Flying Boxcar transport planes from the United States. The reborn Italian aviation industry also began to develop and produce a few ingenious aircraft designs of its own, such as the Fiat G91, the Aermacchi MB-326, the Piaggio Aero P.166 and the line of Agusta-Bell helicopters.