2 1 ▁f igh ters ▁of ▁the ▁V P AF ▁ 9 2 1 st ▁F ighter ▁Regiment ▁were ▁shot ▁down . ▁ ▁St ung ▁by ▁that ▁dev ast ating ▁defeat , ▁the ▁North ▁Vietnam ese ▁Air ▁Force ▁ground ed ▁their ▁f ighter ▁force ▁several ▁times ▁between ▁June ▁and ▁August ▁ 1 9 6 7 , ▁in ▁order ▁to ▁work ▁on ▁their ▁training ▁and ▁tact ics . ▁On ▁ 2 3 ▁August ▁ 1 9 6 7 , ▁the ▁North ▁Vietnam ese ▁Air ▁Force ▁employed ▁their ▁newly ▁de vised ▁t actic ▁against ▁a ▁U . S . ▁strike ▁formation , ▁while ▁it ▁was ▁conduct ing ▁ra ids ▁against ▁a ▁rail ▁yard . ▁The ▁air ▁battle ▁concluded ▁with ▁the ▁US AF ▁losing ▁three ▁F - 4 D ▁f igh ters . ▁ ▁Background ▁ ▁On ▁ 2 ▁March ▁ 1 9 6 5 , ▁the ▁United ▁States ▁Government ▁launched ▁Operation ▁Rol ling ▁Th under , ▁a ▁major ▁bomb ing ▁campaign , ▁with ▁several ▁object ives . ▁First ly , ▁the ▁operation ▁was ▁supposed ▁to ▁ret ali ate ▁against ▁North ▁Vietnam ▁for ▁their ▁military ▁activities ▁inside ▁South ▁Vietnam , ▁thereby ▁raising ▁the ▁mor ale ▁of ▁the ▁South ▁Vietnam ese ▁people , ▁especially ▁the ▁Army ▁of ▁the ▁Republic ▁of ▁Vietnam ▁( AR V N ). ▁Second ly , ▁it ▁aim ed ▁to ▁imp ede ▁North ▁Vietnam ' s ▁ability ▁to ▁w age ▁war ▁by ▁reducing , ▁if ▁not ▁stopping , ▁the ▁flow ▁of ▁men ▁and ▁material ▁into ▁South ▁Vietnam . ▁Third ly , ▁the ▁overall ▁objective