Francis Ridge:
There was a date discrepancy on this case. Ruppelt said it was the 12th and subsequently NICAP listed that date in The UFO Evidence. Project Blue Book, which didn't list this as an "Unknown", showed it clearly as August 5, 6, and the documents (see below) show that this case as "unsolved." This incident always impressed me, and apparently it impressed a lot of others, too. For the die-hard skeptics at Project Blue Book this was the one they had always asked for.  Here was a good UFO sighting. "This was an unknown, one of the best", a ground witnessed visual, with a ground radar tracking, and the pursuit of the object by a jet interceptor that also locked on with its radar, with all the maneuvers independently verified. The UFO was playing a cat & mouse game with an F-84 "Thunderjet",  the first USAF jet fighter able to carry a tactical atomic weapon. Major Lawrence Tacker not only confirmed this case, but he wrote one NICAP member and told him the Air Force had gun-camera photos of the object and radarscope photos. (FSTS,243). Ellsworth AFB is located about 12 miles from Rapid City, and in 1947, the base hosted the 28th Bombardment Wing (BMW), flying the B-29. In July 1949, the 28th began conversion to the gigantic B-36 bomber. Ellsworth was one of the original five Air Force Operational Storage Sites for nuclear weapons, and first received its atomic bombs in 1952.

Joel Carpenter:
I've been checking on the model of F-84 assigned to SAC, and it turns out that the F-84G was the one based at Rapid City at the time. This was a tactical-nuclear-capable day fighter-bomber with straight wings and gun ranging radar.