 Complete the following phrase:  World War I started with Austro-Hungarian declaration of war on Serbia on 28 July 1914. The S.A.F Serbian Air Force saw action from day one. At the beginning of World War I, Serbian pilots who were actually skilled and experienced from the Balkan Wars had succeeded to give the valuable information about the number, the movements, and the position of the enemy troops. They contributed to early Serbian victories in 1914 at 