By the end of July, the Chinese airfields around Antung held more than 300 MiGs; against them, FEAF had 89 F-86As in the theater, not all combat-ready.
The Communist planes charged into battle in large formations, holding an altitude advantage and outnumbering Sabres by four to one. With no hope of further reinforcement from the US, Fifth AF gave up its fighter-bomber strikes in the area under 'MiG Alley'. The Chinese now were flying the MiG-15bis, an improved model with more thrust, operated from rejuvenated airfields. By the winter of 1951, they had driven the B-29s out of the daylight skies.
In December, the 51st FIW converted to new F-86E models and the Sabres now totalled 127, a number meaningful only on paper. About 45 per cent of the planes were out of commission for parts or needed maintenance, the supply of drop tanks had been exhausted, and there were only about 60 Sabres ready to fight instead of 127. For some yet-unexplained reason, the Communist air offensive turned docile in mid-December. They stopped defending the new airfields, and changed their tactics. It looked as if their high command had made a decision to treat the war as a vast training ground, and to cycle pilot classes through an advanced education.
The Chinese and North Koreans had established a joint operations center at the Antung complex of airfields, and had defended it not only with many MiGs, but with a large number of anti-aircraft artillery batteries of medium and large caliber. Additionally, they had installed more than two dozen early-warning radar sets and about a dozen ground-controlled intercept radars. In May 1952 they began sending MiGs out under GCI direction and the air war heated up again.
The Sabre supply was on the increase, and the first F-86F models began to arrive in June. With more thrust, and the solid leading edge replacing the slotted one of earlier models, the F was a more formidable adversary that could stay with the MiGs in maneuvering. It was tried as a fighter-bomber in Korea, because the straight-winged Republic F-84 Thunderjets just couldn't handle the MiGs consistently, although they did a superb job of delivering their heavy ordnance loads on target.
Two wings of F-86F Sabres, the 8th and 18th FBW, were designated to fly fighter-bomber missions, while the 4th and 51st fought for air superiority.