 On 13 February 1913, king Peter I of Serbia adopted the Regulation of the transportation system of devices which run in the air, which made Kingdom of Serbia joining the modern air traffic.It was the fifth country in the world (after Germany, England, France and Austria-Hungary), which regulated legal norms of the air operations.For the Kingdom of Serbia, it was a defense mechanism from Austro-Hungarian planes, which had been flying over Serbian territory, without any permission, since November 1912, as Austro-Hungarian Empire was putting pressure on Serbia to withdraw from the coast of the Adriatic Sea, where Serb units were stationed after the victory over the Turks in the First Balkan War.