How well were Vietnam air forces fighting USAF?
The Vietnamese Air force were extremely effective at attacking and defending against US aircraft throughout the war. Northern Vietnam received a large number of MiG fighter jets from the USSR and China also contributed a large number of supplies and trained their pilots throughout the conflict. The USAF was caught completely off guard by the well trained Vietnamese forces and suffered considerable defeats at the beginning of the war.
The Vietnamese used guerrilla tactics in their sorties and often fought defensively, which made it easier to ambush enemy aircraft and defeat them before support could arrive. The reaction of the USAF was to retrain their pilots and create the “Top Gun” school which readdressed many fighting techniques that had not been studied since the end of WWII. Over time the USAF managed to recover from their early losses but the Vietnamese Air force was still a considerable and constant threat to both ground and air troops.