Dec. 12, 1951.  5 mi SE of Hastings, Minn. (BBU)
3:50 p.m. (CST).  USAF 133rd FI Wing pilot Donald K. "Deke" Slayton [future NASA astronaut] flying F-51 fighter at 10,000 ft at 280-300 mph heading [NW] back to Wold-Chamberlain Field, Minneapolis, Minn., saw a 1-1/2 to 2 ft white (or gray) object off his left wing about 1 mile away and 1,000 ft below flight level [about 10° below local horizon or 8° below earth’s horizon] at (about 8 o’clock position) looking like a kite at first, then like a weather balloon then 2 rapidly counterclockwise revolving discs overlapping with centers about 1 ft apart.  He went into left 180° turn to intercept, approached to about 1,500 ft [heading SE] with object at about 1 o'clock (level ?) position, object accelerated to about 380-400 mph turning to the left, Slayton made 30° bank to turn left with object, but object outpaced him on the outside of turn [heading roughly SW at end of turn], changed appearance to look like a single object, then it made a sudden 45° climbing left turn, accelerated and disappeared.  In 1980 Slayton estimated angular size as grapefruit at arm's length or about 11° but size/distance data indicate about 0.1°.  Wing Intell ofcrs told Slayton a balloon research team [General Mills] sighted the same or similar UFO near a large balloon [Skyhook?] launch.  (Sparks;  Maxwell Microfilm Roll 1, pp. 537-8, 563-4, Roll 9, pp. 660-5;  BB Grudge Status Rpt. 2, pp. 3-4, Rpt. 3, pp. 5-6;  Project 1947;  Richard Haines;  etc.)