Aug. 15-20 (approx.), 1947 Rapid City Air Base [Weaver?], South Dakota (BBU)
Major Hammer sitting in the parking lot near the flight line shortly after dark saw to the NW about 12 elliptical objects about the span of a B-29 (140 ft) with a yellow-white luminous glow in a tight diamond formation, approaching in a shallow descent, level off at about 5,000 ft altitude [height?] at 300-400 mph, make a gentle 110° turn to its right about 4 miles away climbing to the SW, accelerating rapidly. No sound or trail. 1 min? (FOIA; FUFOR Index)

Aug. bt.15-20, 1947; Rapid City AFB, South Dakota (BBU)

9:30 p.m. local. Intelligence Officer Major Elmer H. Hammer observed about 12 elliptical objects in a tight diamond formation at an estimated altitude of 6,000 to 10,000 feet approaching from the NW in a shallow descent moving at an estimated 300-400 mph. The objects then leveled off at approximately 5,000 feet and made a gentle large radius turn of about 110 degrees to the right about 4 miles from the observer. The objects started climbing at an angle of 30 to 40 degrees and appeared to accelerate rapidly in the climb. The objects were approximately 100 feet long and had a brilliant yellow-white luminous glow. No sound was heard from the objects. The objects sighted were visible for approximately 1 minute.

Fran Ridge:
This is one of the reports cited in the notes about the Top Secret EOTS which quoted an interview with this Major from the Rapid City AFB (now Ellsworth AFB) who said he saw twelve UFOs flying a tight formation.

Detailed reports and documents
reports/470815rapidcity_report.htm (Dan Wilson)