8 th ▁and ▁ 3 6 6 th ▁T act ical ▁F ighter ▁W ings ▁fle w ▁in ▁a ▁formation ▁which ▁res emble d ▁an ▁F - 1 0 5 ▁strike ▁force , ▁towards ▁the ▁V P AF ' s ▁Ph uc ▁Y en ▁Air ▁Base . ▁There ▁were ▁four ▁fl ights ▁of ▁F - 1 0 4 ▁f igh ters ▁flying ▁in ▁esc ort , ▁to ▁simulate ▁the ▁F - 4 s . ▁ ▁When ▁the ▁U . S . ▁f ighter ▁form ations ▁were ▁detected ▁by ▁North ▁Vietnam ese ▁rad ar , ▁Mi G - 2 1 ▁f igh ters ▁of ▁the ▁V P AF ▁ 9 2 1 st ▁F ighter ▁Regiment ▁based ▁at ▁Ph ú c ▁Y ên ▁Air ▁Base ▁and ▁K ép ▁Air ▁Base ▁were ▁immediately ▁placed ▁on ▁category ▁one ▁red ▁alert , ▁which ▁was ▁the ▁highest ▁state ▁of ▁alert . ▁However , ▁unknown ▁to ▁the ▁U . S . ▁pil ots ▁at ▁the ▁time , ▁the ▁V P AF ▁High ▁Command ▁forb ade ▁their ▁pil ots ▁from ▁taking ▁off ▁until ▁U . S . ▁f igh ters ▁were ▁ ▁away ▁from ▁No i ▁B ai . ▁A part ▁from ▁the ▁late ▁reaction ▁of ▁the ▁V P AF ▁High ▁Command , ▁weather ▁conditions ▁over ▁North ▁Vietnam ▁also ▁fav ored ▁U . S . ▁air cre ws ; ▁North ▁Vietnam ese ▁bases ▁at ▁No i ▁B ai ▁and ▁K ep ▁were ▁covered ▁by ▁ 1 0 / 1 0 th ▁cloud , ▁which ▁started ▁at ▁a ▁height ▁of ▁