Misawa AFB 7th Fighter Bomber Squadron USAF pilot Second Lieutenant James Henry Petty was flying F-80C jet fighter in a slight turn to the left at 25,000 feet 320 mph (IAS?) heading northeast about 45° azimuth to meet up with a lead aircraft (apparently another F-80C) piloted by Lieutenant Sofbom of 7th Fighter Bomber Squadron, also heading northeast at 45° at this point in a sharper gradual left turn, when he saw an unidentified object about three miles away at his two o'clock position following the lead aircraft in a tracking position about 1,000 feet below and to the right-rear from the lead aircraft traveling about 275-300 mph, silhouetted against clouds. During the lead aircraft's wide left turn that eventually resulted in a 260° heading, the UFO "accelerated" and pulled up to level position (at three o'clock) and climbed to the lead plane's altitude while the F-80C rapidly approached and overflew both the lead aircraft and UFO, having to climb to avoid collision, but getting "a very good look from the top and both sides" of the UFO, Petty saw that it was a rectangular cream-colored flat object appearing to be made of "muslin" about 20 feet high, 60 feet long, but only about two inches thick, oriented vertically, not reflecting sunlight despite bright sun, no exhaust, no apparent means of propulsion, not wavering or fluttering. Petty first thought it was an aerial tow target but knew there was no aerial gunnery scheduled. After being overflown, UFO pulled away from lead aircraft, accelerated to 600 mph on a 330° heading, overtook and crossed in front of Petty's F-80C from behind and left to right and disappeared in the distance against a clear sky. Similar incident next day near Wakkanai.

Google map of this location.