i ▁and ▁H ai ▁Ph ong , ▁they ▁were ▁ag gress ively ▁challeng ed ▁by ▁North ▁Vietnam ese ▁Mi G ▁f igh ters . ▁ ▁P rel ude ▁The ▁year ▁of ▁ 1 9 6 7 ▁started ▁badly ▁for ▁the ▁Vietnam ▁People ' s ▁Air ▁Force ▁( VP AF ). ▁During ▁the ▁early ▁years ▁of ▁the ▁war , ▁the ▁rules ▁of ▁eng agement ▁prevent ed ▁U . S . ▁f ighter - b om bers ▁from ▁hitting ▁North ▁Vietnam ese ▁air ▁bases , ▁and ▁that ▁allowed ▁North ▁Vietnam ese ▁f ighter ▁pil ots ▁to ▁attack ▁American ▁bom ber ▁form ations ▁as ▁they ▁were ▁approaching ▁their ▁targets , ▁thereby ▁forcing ▁U . S . ▁pil ots ▁to ▁j ett ison ▁their ▁bomb ▁loads ▁before ▁they ▁even ▁reached ▁their ▁target . ▁Then , ▁instead ▁of ▁du eling ▁with ▁U . S . ▁strike ▁aircraft , ▁North ▁Vietnam ese ▁pil ots ▁would ▁normally ▁retre at ▁to ▁the ▁safety ▁of ▁their ▁bases . ▁To ▁pre empt ▁further ▁attacks ▁on ▁U . S . ▁bom ber ▁form ations ▁by ▁the ▁North ▁Vietnam ese ▁Air ▁Force , ▁the ▁United ▁States ▁Air ▁Force ▁became ▁interested ▁in ▁l uring ▁North ▁Vietnam ese ▁Mi G ▁f igh ters ▁up ▁against ▁a ▁de co y ▁target , ▁and ▁shoot ▁them ▁down ▁in ▁the ▁air ▁using ▁miss ile - ar med ▁f ighter ▁aircraft . ▁By ▁ 1 9 6 7 , ▁the ▁North ▁Vietnam ese ▁Air ▁Force ▁had ▁become ▁more ▁ag gress ive ▁towards ▁U . S . ▁strike ▁form ations , ▁and