From Wikipedia

Vietnam
Episode Nine

Air War Vietnam

The Vietnam Air Force (VNAF) was originally equipped with helicopters such as the CH-21 and propeller powered aircraft such as the T-28 Trojan when jet aircraft were disallowed by treaty. As US involvement increased, most airpower was directly flown by US forces.

Large scale use of helicopters by the US Army in Vietnam led to a new class of airmobile troops, and the introduction of "Air Cavalry" in the U.S, culminating in extensive use of the UH-1 Huey helicopter which would become a symbol of that war, while the CH-54 Tarhe "Skycrane" and CH-47 Chinook lifted heavier loads such as vehicles or artillery. Troops were able to land unexpectedly, strike, and leave again, and evacuate wounded. The specialized AH-1 Cobra was developed from the Huey for escort and ground support duties.

US forces provided close support of ground force over South Vietnam, and strategic bombing of targets over North Vietnam. Many types flying close support or COIN (Counter Insurgency Warfare) missions were propeller powered types such as the O-1 and OV-10 Bronco FAC spotters, A-1 Skyraider, B-26 Invader, and AC-47 "Spooky" gunship. C-123 Provider and C-130 Hercules transports flew supplies into battlefields such as Khe Sanh. "Fast movers" included the supersonic F-100 Super Sabre, while the giant B-52 Stratofortress would be modified to unload a massive high explosive payload on enemy troop concentrations The AC-130 would become the ultimate gunship, while the AX specification to replace the Skyraider would evolve into the A-10 Thunderbolt II

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