- air craft ▁def ences ▁of ▁Bel grade ▁briefly ▁attempted ▁to ▁meet ▁the ▁over wh el ming ▁Luft wa ffe ▁assault , ▁but ▁were ▁elimin ated ▁as ▁thre ats ▁during ▁the ▁first ▁wave ▁of ▁the ▁attack . ▁S ources ▁vary ▁regarding ▁the ▁success ▁achieved ▁by ▁the ▁def enders . ▁A ▁US ▁Army ▁study ▁first ▁published ▁in ▁ 1 9 5 3 ▁states ▁that ▁the ▁Luft wa ffe ▁lost ▁two ▁f ighter ▁aircraft , ▁down ed ▁ 2 0 ▁Y ug oslav ▁aircraft ▁and ▁destroyed ▁a ▁further ▁ 4 4 ▁on ▁the ▁ground . ▁The ▁military ▁historian ▁Daniel ▁L . ▁Z aj ac ▁writes ▁that ▁the ▁Germ ans ▁lost ▁ 4 0 ▁aircraft ▁during ▁the ▁two - day ▁air ▁battle . ▁Another ▁source ▁indicates ▁the ▁loss ▁of ▁ 1 4 ▁German ▁aircraft ▁on ▁ 6 ▁April . ▁D ive - b om bers ▁in ▁subsequent ▁waves ▁were ▁able ▁to ▁operate ▁at ▁ro o ft op ▁alt itude . ▁ ▁According ▁to ▁the ▁historian ▁Ste van ▁K . ▁Pav low itch , ▁the ▁bomb ing ▁of ▁Bel grade ▁last ed ▁three ▁days . ▁Other ▁sources ▁state ▁the ▁air ▁battle ▁over ▁Bel grade ▁last ed ▁only ▁two ▁days ▁ow ing ▁to ▁poor ▁flying ▁conditions ▁on ▁ 8 ▁April . ▁The ▁most ▁important ▁cultural ▁institution ▁that ▁was ▁destroyed ▁was ▁the ▁National ▁Library ▁of ▁Ser bia , ▁which ▁was ▁hit ▁by ▁bomb s ▁and ▁g utt ed ▁by ▁fire . ▁H undred s ▁of ▁thousands ▁of ▁rare ▁books , ▁maps , ▁and ▁medieval ▁manuscript s ▁were ▁destroyed .