▁emb ass y ▁had ▁informed ▁its ▁government ▁that ▁Bel grade ▁did ▁not ▁contain ▁any ▁anti - air craft ▁def ences , ▁but ▁in ▁an ▁effort ▁to ▁justify ▁the ▁attack ▁to ▁the ▁public , ▁German ▁propag anda ▁brand ed ▁the ▁city ▁" F ort ress ▁Bel grade " ▁after ▁the ▁first ▁bomb s ▁were ▁dropped . ▁ ▁By ▁ 6 ▁April , ▁the ▁V V K J ▁had ▁been ▁almost ▁completely ▁mobil ised , ▁and ▁consisted ▁of ▁four ▁air ▁brig ades ▁with ▁more ▁than ▁ 4 2 3 ▁aircraft ▁of ▁Y ug oslav , ▁German , ▁Italian , ▁French , ▁Czech ▁and ▁British ▁design , ▁including ▁ 1 0 7 ▁modern ▁f igh ters ▁and ▁ 1 0 0 ▁modern ▁medium ▁bom bers . ▁Other ▁than ▁a ▁small ▁number ▁of ▁locally ▁made ▁Rog o ž ar ski ▁I K - 3 ▁f igh ters , ▁almost ▁all ▁the ▁modern ▁aircraft ▁available ▁to ▁the ▁V V K J ▁were ▁of ▁German , ▁Italian ▁or ▁British ▁design ▁for ▁which ▁limited ▁sp ares ▁and ▁m un itions ▁were ▁available . ▁The ▁available ▁aircraft ▁were ▁spread ▁all ▁over ▁the ▁country , ▁and ▁only ▁the ▁ 1 st ▁F ighter ▁Brigade ▁was ▁near ▁enough ▁to ▁Bel grade ▁to ▁respond ▁to ▁an ▁attack ▁on ▁the ▁capital . ▁In ▁total , ▁the ▁ 1 st ▁F ighter ▁Brigade ▁field ed ▁ 5 6 ▁Mess ersch mitt ▁B f ▁ 1 0 9 E - 3 a ▁f igh ters , ▁ 1 5 ▁Haw ker ▁H urr icane ▁M k Is