Most lines would be extended to the inner suburbs. The first to leave the city proper was Line 9, extended in 1934 to Boulogne-Billancourt; more followed in the 1930s. World War II forced authorities to abandon projects such as the extension of Line 4 and Line 12 to the northern suburbs. By 1949, eight lines had been extended: Line 1 to Neuilly-sur-Seine and Vincennes, Line 3 to Levallois-Perret, Line 5 to Pantin, Line 7 to Ivry-sur-Seine, Line 8 to Charenton, Line 9 to Boulogne-Billancourt, Line 11 to Les Lilas and Line 12 to Issy-les-Moulineaux.