A very large, bright blip presentation on the scope, inbound to the scope centre then reversing and going back out on the same set of trace radii, is typical of some cyclical source of noise or interfenece - possibly radar interference caused by the spray of pulses from another radar or radars with a slightly different prf and scan rate. It might happen only briefly because of AP conditions. The skew-T plot in the file shows a rather steep
looking inversion at about 2000 ft which could be responsible and a humid layer higher up (humidity gradients are much more important than temperature for radio refractivity).What makes me think that the AF may have been right to suspect internal noise in this case is that the blip always appears right on the 10-mile range rings, suggesting a signal source related to the internal eletronics (the range rings are electronically painted on the tube of course).
In fact a transcript of one operator's phone conversation with another radar facility in real time says not only that the other radar was picking up radar interference in the area reported, but the Patuxent operator was himself seeing interference each time the odd blips appeared. The file says 20 other facilities in the area were checked later but no contacts were made by any other radars. The Patuxent operator himself reports that nothing was showing up on his own "long range" radar, only on one scope.
The visual in the same area alluded to (in the CIA document) is really so vague and third hand it's a rumour. It isn't possible to comment on it and it appears to me that this was only shaken out later because of public excitement, not properly reported or documented at the time.
The file says that Patuxent didn't bother to report the incident at first because personnel didn't think it was of importance, i.e. they dismissed the blips as noise/interference at the time. Clearly it was the fact that a story got into the papers and was given prominence by Keyhoe and Hall at NICAP that caused a belated interest in trying to get information, but at first they couldn't even get the date right (one of the witnesses continued
to maintain that the true date was Dec 29, not Dec 19).
Claims by Keyhoe and others that the AF were rubbishing a Navy report by denigrating Navy competence find no support from the original documents. All information relating to the behaviour of the blips, the absence of confirming tracks by other radars, the relative competences of the three named operators*, and virtually all other info diagnostic of the conclusion that this was an insignificant radar noise/interference artifact inflated by bad press into a saucer story - including that conclusion itself - all of this comes from Navy documents following internal Navy investigation. BB merely passed on the Navy conclusions, with minimal action or commentary (limited mainly to requesting the info from the Navy, requesting an AF meteorologist's temp/dewpoint profile for the area, and maintaining a log of phone calls and letters).
* The Navy documents record that the youngest, least experienced and least reliable of the three - Sujka - was not only the one responsible indirectly for the rumour and the press story, but was the only one of the three who felt the blips were more than noise, and was also the only one of the three to mislead the Navy investigation by giving the wrong date - TWICE, first as Dec 29, then as Dec 28.