Evaluation of the Fort Monmouth Incident
September 10, 1951

Dr. James E. McDonald:

1. Case 31. Ft. Monmouth, N.J., September 10, 1951. 

It is clear from Ruppelt' s discussions (Ref. 5) that a series of radar and visual sightings near Ft. Monmouth on 9/10/51 and the next day were of critical importance in affecting official handling of the UFO problem in the ensuing two-year period. Many details from the official file on these sightings are now available for scientific scrutiny (Ref. 7). Here, a sighting by two military airmen flying in a T-33 near Ft. Monmouth will be selected from that series of events because the sighting was eventually tagged as a weather balloon. As with any really significant UFO case, it would require far more space than can be used here to spell out adequately all relevant details, so a very truncated account must be employed. While flying at 20,000 ft from a Delaware to a Long Island airbase, the two men in the T-33 spotted an object "round and silver in color" which at one stage of the attempted intercept appeared flat. The T-33 was put into a descending turn to try to close on the object but the latter turned more tightly (the airmen stated) and passed rapidly eastward towards the coast of New Jersey and out to sea. A pair of weather balloons (probably radiosonde balloons but no information thereon given in the files) had been released from the Evans Signal Laboratory near Ft. Monmouth, and the official evaluation indicates that this is what the airmen saw. 

However, it is stated that the balloons were released at 1112 EDST, and the sighting began at about 1135 EDST with the T-33 over Point Pleasant, N.J. In that elapsed time, a radiosonde balloon, inflated to rise at the 800-900 ft/min rate used for such devices, would have attained an altitude of about 17-18,000 ft, the analysis notes. From this point on, the official analysis seems to be built on erroneous inferences. The airmen said that, as they tried to turn on the object, it appeared to execute a 120-degree turn over Freehold, N.J., before speeding out over the Atlantic. But from the upper winds for that day, it is clear that the Ft. Monmouth balloon trajectory would have taken it to the northeast, and by 1135, it would have been about over the coast in the vicinity of Sea Bright. Hence, at no time in the interval involved could the line of sight from T-33 to balloon have intersected Freehold, which lies about 15 miles WSW of the balloon release- point. Instead, had the airmen somehow seen the radiosonde balloon from Pt. Pleasant, it would have lain to about their N or NNE and would have stayed in about that sector until they passed it. Furthermore, the size of the balloon poses a serious difficulty for the official analysis. Assuming that it had expanded to a diameter of about 15 feet as it ascended to about the 18,000-ft level, it would have subtended an arc of only 0.6 min, as seen from the T-33 when the latter passed over Pt. Pleasant. This angular size is, for an unaided eye, much too small to fit the airmen's descriptions of what they tried to intercept. In a press interview (Ref. 40), the pilot, Wilbert S. Rogers of Columbia, Pa., said the object was "perfectly round and flat" and that the center of the disc was raised "about six feet" and that it appeared to be moving at an airspeed of the order of 900 mph. The entire reasoning on which the balloon evaluation is elaborated fails to fit readily established points in the official case-summary. 


The possibility that a pilot can be misled by depth perception errors and coordinate-reference errors to misconstrue a weather balloon as a fast-maneuvering object must always be kept in mind. But in the Ft. Monmouth instance, as in many others that could be discussed in detail, there is a very large gap between the balloon hypothesis and the facts. The basic sighting-report here is quite similar to many other daytime sightings by airborne observers who have seen unconventional disc-like objects pass near their aircraft. 

Dr. James E. McDonald