The Kingdom of Bulgaria entered World War I as an ally of the Central Powers on 4 October 1915. The Aeroplane Section of the Bulgarian Army was reformed with assistance from Germany and Austria. Aircraft were deployed to Kumanovo Airfield in support of advancing Bulgarian forces, but bad weather initially prevented any flying. Until then they had completed 11 combat sorties from an airfield in Sofia (now the central railway station). As the frontline advanced, the unit re-deployed to airfields near Belitsa and Xanthi, in modern Greece. Newly acquired German LVG aircraft were hastily pressed into action. Two more airfields were constructed near Udovo and Levunovo. The Allies began flying reconnaissance and bomber sorties against Bulgarian units on the Southern Balkan Front. Throughout World War I Bulgarian military aviation experienced a steady increase in both numbers and quality of aircraft; however, they remained inferior to those flown by the Allies, especially the British and French. The First Aeroplane Section (the country's only aircraft unit) was attached to the Second Bulgarian Army. It flew 255 sorties compared to 397 flown by the four squadrons of the Entente it opposed, and operated the following types: