At the outbreak of the Korean War, the United States Air Force (USAF) had >1000 aircraft in the Pacific region.
Immediately mustered against the North Korean invasion were F-80 Shooting Stars, F-82 Twin Mustangs, B-26 Invaders and B-29 Superfortresses. USAF aircraft were well-equipped and flew from many bases in Japan—out of North Korean reach.
The North Korean People’s Air Force (KPAF) had 2000 personnel and 132 aircraft.
From June 25 to July 20, 1950 North Korean aircraft waged a battle for air supremacy over South Korea.
In the initial phase of the war, North Korean aircraft held air superiority over South Korea.
Despite unsuccessful UN ground action in the early stage of the Korean War, the air battle was successful for UN forces.
After destruction of the small KPAF, the UN air force concentrated attacks on North Korean ground forces, inflicting heavy casualties. In addition, UN bombing of North Korean armor, supplies and ports, greatly hampered enemy efforts to penetrate the Pusan Perimeter.
U.N. bombing continued relatively unhindered for six months of the war ~ until the ominous appearance of the Soviet-built MiG-15 fighter (presumably flying out of Manchuria).