Communist China MiG-17 shot down two ROCAF F-84G, killing one of the two pilots, on July 29, 1958. These MiGs were among those deployed to Swatow (汕頭) after the Chinese Communist Party (CCP) Central Military Commission held a meeting on July 18. During the meeting, it was decided that Quemoy should be shelled and additional PLA Air Force fighters should be deployed to Fujian Province. On July 27, 48 MiG-17 took position in the two air bases at Liencheng, Fujian, and Swatow, Guandong.
As the tension across Taiwan Strait was increasing, CIA Det C deployed the U-2 to Okinawa again and Lyle Rudd flow Mission 6017 over China on August 20, 1958, only three days before the shelling. Compared with Mission 6012 on June 19, the area covered by Mission 6017 was further down south. It also covered inland China, as far as Jiangxi Province.
According to the Mission Coverage Summary, Mission 6017 revealed as many as 400 MiG-15/MiG-17 on the airfields covered:
The intelligence obtained from Mission 6017 also indicated the movement of artillery toward Amoy (廈門) near Quemoy, as shown in the following document. However, this intelligence might have come too late since it was dated August 29. Processing and interpretating the images do take time.
