▁Also ▁struck ▁was ▁the ▁Bel grade ▁Z oo , ▁sending ▁fright ened ▁animals ▁running ▁through ▁the ▁streets . ▁ ▁British ▁ret ali ation ▁ ▁No . ▁ 3 7 ▁Squadron ▁of ▁the ▁Royal ▁Air ▁Force ▁( RA F ) ▁conducted ▁two ▁bomb ing ▁ra ids ▁on ▁Sof ia , ▁the ▁capital ▁of ▁Bulg aria , ▁in ▁ret ali ation ▁for ▁the ▁bomb ing ▁of ▁Bel grade . ▁Oper ating ▁V ick ers ▁Well ington ▁bom bers ▁from ▁an ▁air field ▁in ▁Greece , ▁the ▁squad ron ▁conducted ▁ra ids ▁on ▁ 6 / 7 ▁April ▁and ▁ 1 2 / 1 3 ▁April , ▁dro pping ▁a ▁total ▁of ▁ ▁of ▁high - expl os ive ▁bomb s ▁on ▁railway ▁targets ▁and ▁nearby ▁resident ial ▁areas . ▁These ▁ra ids ▁were ▁carried ▁out ▁despite ▁the ▁fact ▁that ▁Britain ▁was ▁not ▁at ▁war ▁with ▁Bulg aria ▁until ▁ 1 2 ▁December ▁ 1 9 4 1 . ▁The ▁historian ▁H erman ▁Kn ell ▁calls ▁the ▁ret ali atory ▁just ification ▁for ▁these ▁ra ids ▁" st range ▁and ▁imp laus ible ". ▁The ▁av iation ▁histor ians ▁Sh ores , ▁C ull ▁and ▁Mal izia ▁indicate ▁that ▁these ▁ra ids ▁were ▁attacks ▁on ▁the ▁lines ▁of ▁communication ▁of ▁German ▁forces ▁attack ing ▁Greece ▁and ▁Y ug oslav ia , ▁and ▁note ▁that ▁the ▁ra id ▁on ▁ 6 / 7 ▁April ▁target ed ▁an ▁am mun ition ▁train ▁and ▁other ▁install ations ▁in ▁Sof ia , ▁and ▁the ▁ra id ▁on ▁ 1 2