 While its strength in ground forces initially overwhelmed UN forces, the Chinese People's Liberation Army Air Force (PLAAF) was, at the time, small and no better equipped than the KPAAF.While the Soviet Union never officially entered the war, on 1 November 1950, the 64th Fighter Aviation Corps (64 IAK) of the Soviet Air Forces was attached to the PLAAF, under the 1st United Air Army.That same day, Soviet-piloted MiG-15s began operating over North Korea and the first clashes between MiG-15s and US aircraft occurred, when eight aircraft from the Soviet Air Forces intercepted about 15 United States Air Force P-51 Mustangs flying a ground support mission.