▁Y ug oslav ▁coup ▁d ' état . ▁He ▁was ▁replaced ▁by ▁his ▁ 1 7 - year - old ▁nep hew ▁Peter . ▁ ▁Pre par ations ▁▁ ▁The ▁day ▁of ▁the ▁coup , ▁Hitler ▁issued ▁Direct ive ▁ 2 5 , ▁which ▁stated ▁that ▁the ▁coup ▁had ▁changed ▁the ▁political ▁situation ▁in ▁the ▁B alk ans . ▁He ▁ordered ▁that ▁" even ▁if ▁Y ug oslav ia ▁at ▁first ▁should ▁give ▁declarations ▁of ▁loyal ty , ▁she ▁must ▁be ▁considered ▁as ▁a ▁fo e ▁and ▁therefore ▁must ▁be ▁destroyed ▁as ▁quickly ▁as ▁possible ". ▁German ▁reconna issance ▁aircraft ▁frequently ▁viol ated ▁Y ug oslav ▁air space ▁in ▁the ▁after math ▁of ▁the ▁coup . ▁V V K J ▁f igh ters ▁were ▁placed ▁on ▁constant ▁alert . ▁The ▁German ▁inc urs ions ▁demonstrated ▁that ▁the ▁Y ug oslav ▁ground ▁observation ▁post ▁network ▁and ▁supporting ▁radio ▁communic ations ▁were ▁in ade qu ate . ▁Hitler ▁decided ▁that ▁Bel grade ▁would ▁be ▁bom bed ▁as ▁pun ishment ▁for ▁the ▁coup , ▁under ▁the ▁cod ename ▁Operation ▁Ret ribution ▁( Un ter nehmen ▁St raf gericht ). ▁On ▁ 2 7 ▁and ▁ 2 8 ▁March ▁ 1 9 4 1 , ▁Reichs mar sch all ▁Hermann ▁G ör ing ▁transferred ▁about ▁ 5 0 0 ▁f ighter ▁and ▁bom ber ▁aircraft ▁from ▁France ▁and ▁northern ▁Germany ▁to ▁air fields ▁near ▁the ▁Y ug oslav ▁border . ▁The ▁commander ▁of ▁Luft fl otte ▁IV , ▁General ober st ▁( General ) ▁Alexander ▁Lö hr