▁found ▁that ▁standard ▁military ▁units , ▁based ▁on ▁relatively ▁inf lex ible ▁tables ▁of ▁organization , ▁were ▁not ▁prov ing ▁to ▁be ▁well ▁adapted ▁to ▁the ▁training ▁mission . ▁ ▁According ly , ▁it ▁adopted ▁a ▁more ▁functional ▁system ▁in ▁which ▁each ▁base ▁was ▁organized ▁into ▁a ▁separate ▁number ed ▁unit , ▁while ▁the ▁groups ▁and ▁squad rons ▁acting ▁as ▁replacement ▁training ▁units ▁were ▁dis band ed ▁or ▁in activ ated . ▁This ▁resulted ▁in ▁the ▁ 3 3 1 st , ▁along ▁with ▁other ▁units ▁at ▁Cas per , ▁being ▁in activ ated ▁in ▁the ▁spring ▁of ▁ 1 9 4 4 ▁and ▁being ▁replaced ▁by ▁the ▁ 2 1 1 th ▁A AF ▁Base ▁Unit ▁( Com bat ▁C rew ▁Training ▁Station , ▁He avy ), ▁which ▁assumed ▁the ▁ 3 3 1 st ▁Group ' s ▁mission , ▁personnel , ▁and ▁equipment . ▁ ▁Very ▁heavy ▁bom ber ▁operations ▁Red es ign ated ▁ 3 3 1 st ▁Bomb ard ment ▁Group ▁( V ery ▁He avy ). ▁Activ ated ▁on ▁ 1 2 ▁July ▁ 1 9 4 4 ▁at ▁Dal hart ▁A AF ld , ▁Texas . ▁Ass igned ▁to ▁Second ▁Air ▁Force . ▁Tra ined ▁for ▁combat ▁with ▁B - 2 9 B ' s ▁initially ▁at ▁Dal hart , ▁then ▁to ▁McC ook ▁A AF ld , ▁Neb r aska . ▁ ▁The ▁ 3 3 1 st ▁was ▁assigned ▁the ▁B - 2 9 B ▁model . ▁This ▁model ▁was ▁built ▁at ▁Bell - At