 The first civilian aircraft to fly over Serbia before the end of World War I postal service flights carrying mail.In cooperation with the Postal and Telegraphic Department several flights were organized in Thessaloniki, where pilots of the First Serbian Squadron, AP 521, carried mail between Skopje and Thessaloniki.When the Kingdom of Serbs, Croats and Slovenes was established in December 1918, two-seaters Breguet 14 flew a regular route from Novi Sad through Belgrade and Niš to Skopje almost daily.