, ▁after ▁they ▁had ▁exam ined ▁U . S . ▁air ▁tact ics , ▁North ▁Vietnam ese ▁command ers ▁decided ▁that ▁Mi G - 1 7 ▁pil ots ▁should ▁attack ▁U . S . ▁form ations ▁from ▁either ▁side , ▁while ▁Mi G - 2 1 ▁pil ots ▁would ▁strike ▁from ▁above . ▁Before ▁the ▁North ▁Vietnam ese ▁Air ▁Force ▁could ▁implement ▁their ▁new ▁tact ics , ▁however , ▁the ▁V P AF ▁ 9 2 1 st ▁F ighter ▁Regiment ▁was ▁with dra wn ▁from ▁combat ▁for ▁several ▁months ▁to ▁recover ▁from ▁the ▁blo ody ▁defeat ▁it ▁had ▁suffered ▁as ▁a ▁result ▁of ▁Operation ▁B olo . ▁ ▁In ▁April , ▁North ▁Vietnam ese ▁Mi G ▁f igh ters ▁were ▁back ▁in ▁the ▁air ▁to ▁challenge ▁U . S . ▁Navy ▁and ▁Air ▁Force ▁f ighter - b om bers ▁again , ▁but ▁they ▁only ▁experienced ▁mixed ▁results ▁with ▁heavy ▁losses . ▁As ▁a ▁result , ▁between ▁late ▁June ▁and ▁early ▁August ▁ 1 9 6 7 , ▁North ▁Vietnam ese ▁Air ▁Force ▁f igh ters ▁were ▁ground ed ▁several ▁times , ▁so ▁their ▁pil ots ▁could ▁work ▁on ▁their ▁training ▁and ▁new ▁tact ics . ▁While ▁the ▁North ▁Vietnam ese ▁pil ots ▁were ▁under going ▁training , ▁American ▁air power ▁was ▁concentr ated ▁on ▁striking ▁at ▁H ano i ' s ▁line ▁of ▁communic ations , ▁especially ▁the ▁rail ▁lines ▁running ▁north - east ▁and ▁north - west ▁into ▁China , ▁and ▁the ▁transport ation ▁network ▁which ▁linked ▁North ▁Vietnam '