Date: Wed, 16 Mar 2011 11:29:14 -0500
Subject: February 2, 1952 TIME: night CLASS: R/V shipboard radar/deck visual
Source: Radar Catalogue: A Review of Twenty One Ground and Airborne Radar UAP Contact Reports
              Generally Related to Aviation Safety for the Period October 15, 1948 to September 19, 1976


5. DATE: February 2, 1952 TIME: night CLASS: R/V shipboard radar/deck visual

LOCATION: SOURCES: Hynek (1978) 126

Sea of Japan

Near S. Korean coast

RADAR DURATION: approx. 10 minutes

EVALUATIONS: Blue Book - unknown

PRECIS: The aircraft carrier USS Philippine Sea was making 13 knots on a 180-degree (S) heading off the E coast of Korea. A single target was detected on radar at 0 degrees (N) range 25 miles approaching the ship. At range 20 miles the target began a wide turn to the E, radius 11-12 miles. The radar operator queried the aircraft controller for an ID of the target. At this point three signal observers on deck independently reported visual sightings to the bridge of an object or objects resembling three "exhaust flames" at 30 degrees elevation and turning away from the ship at the same azimuth as the radar target, which at this time was shown at an altitude of 52,000', range 17 miles and increasing. The aircraft controller determined that the target was not a friendly aircraft, and the general alarm was sounded. The target continued to turn away onto a heading approximately NW until it returned to a 0-degree bearing from the carrier, range now 55 miles, where it split and opened as 2 contacts several miles apart. At this point the radar operator began to make "careful plots, checking constantly" for 3 minutes while the 2 targets headed N abreast on a slightly zigzag course, fading from the scope at range 110 miles. During this period the targets accelerated:

"Measured speed 10 miles per minute (600 mph) for first minute, 15 miles per minute (900 mph) for second minute, 30 miles per minute (1800 mph) for third minute."

NOTES: According to Hynek's commentary on the intelligence report: "During the time it was in view, the coast of Korea and the island of Ullung Do were visible at a distance of twenty miles, and an escorting destroyer was visible on the scope 2,000 yards from the carrier." Presumably this means that the coast and island were both seen on radar, rather than visually, although this is unclear. But it should be noted that Ullung Do is some 80 miles from the nearest point on the coast of South Korea at Ulchin, so that at no time could the ship have been 20 miles from both. However this inconsistency is probably an introduced error, and should not be taken to signify any extraordinary propagation conditions.

The radarscope map of the incident is consistent with all speeds, ranges and azimuths cited. It should also be emphasised that independent visual observers estimated the elevation of the "exhaust flames" as 30 degrees when turning past the ship, whilst radar at this point showed the target at 17 miles (slant) range, altitude 52,000', or almost exactly 30 degrees. It is worth noting that at this point it would be irrational to conclude that the target was anything other than aircraft, and if the incident had ended there no "UFO" report would have been submitted. Even the separation of the target would not of itself challenge this conclusion, since more than one aircraft flying within the resolution cell could be displayed as a single echo, and the three "exhaust flames" could be said to confirm this interpretation.

However, the rather careful plotting of speeds up to 1800 mph instantly changes the complexion of the incident, and once it has become a "UFO report" it invites us to attempt all manner of contorted interpretations. The question in a case such as this is whether the a priori improbability of a "UFO" (whatever that might mean) outweighs the prima facie probability that a target consistently tracked on radar and confirmed visually was physically present. This question is not answerable in practice. Suffice it to say that the radar incident has no easy explanation in terms of super-refractive AP of sea clutter or surface ships, partial inversion reflection, CAT, birds, insects, balloons or other wind borne objects, side lobe returns, multiple-trip returns from targets beyond the unambiguous range, spurious internal signals or RFI. A "ghost" echo from an efficient surface reflector (say, the angle made by the side of a ship with the sea - a destroyer was in the vicinity) received via an aircraft as primary reflector might achieve the speeds reported, but: a) no such aircraft, which must ex hypothesi have been within the radiation pattern, was separately detected, and no known aircraft were reported to be in the area; and b) a total radar duration on the order of 10 minutes and a track painted continuously to a range of 110 miles makes any ghost reflection involving a ship only ? mile away extremely improbable. (A ghost reflection with the ship as primary reflector could not achieve the >45 degrees change in azimuth reported, being displayed always on the ship's true azimuth.)

The target behavior appears to have been rational and consistent, without erratic jumps, disappearances or course-reversals, executing a smooth turn with a radius of some 12 miles in the manner of an aircraft, though at somewhat high altitude. Together with multiple independent visual sightings at a position consistent with the concurrent radar target, it is reasonable to conclude that the incident was most probably caused by a real radar-reflective object or objects emitting light resembling that from an aircraft exhaust. However no aircraft in 1952 was remotely capable of speeds up to 1800 mph, and this is the crux of the case: if the displayed speed can be explained then the object(s) can be explained as probable aircraft.

The intelligence report has this to say, pertinent to the possibility of operator error:

A thorough debriefing was made of the radar operator. Personnel stated that the operator was very intelligent, efficient and cooperative. Operator was cognizant of capabilities and limitations of the radar equipment . . . . The three minutes of careful plotting were made after the object had turned and was heading away from the station. Operator was sure of the accuracy of the plots for the three minutes, and was adamant that the speeds shown were approximately correct.

The likelihood of gross malfunction in the radar display(s) would appear to be minimised by the very close match with the visual azimuth and elevation reported as the target turned past the ship. It is conceivable, however, that there was a range-scale error on the PPI. If, for example, a selected range-scale of 100 miles was actually giving a 30-mile scale due to electromechanical fault, and if the operator failed to notice the error, then there would be a factor-three error in plotted ranges, leading to a true maximum speed on the order of 600mph during the final 60 seconds of the track - roughly the maximum speed of, say, an F-94 in a powered descent. Angular position and motion would of course be preserved.

This hypothesis is highly speculative and, it must be said, not particularly plausible. It is first of all unlikely that an operator with the stated experience would neglect to notice so basic a fault during or after the ten minutes or so of the event whilst making "careful plots, checking constantly", evidently cognisant of the abnormal nature of the track, and the (presumably known) position of the escort destroyer - concurrently displayed at 2000 yards from the carrier - would have been an unmissable and constant reference datum on-scope long before and long after the appearance of the target, not to mention the coasts of Korea and Ullong Do island. (The aforementioned ambiguity in the stated range of these land echoes is unfortunately not relevant to this hypothesis, since: a) if there is an original error here it is in the wrong direction - that is, the displayed range would be exaggerated by 3 to 120 miles, not reduced to 20 miles; and b) it is anyway much more likely that this is a constructional error in Hynek's case summary, the figure of 20 miles referring either to the mainland or to Ullong Do, clearly not to both.)

In conclusion there appears to be no reasonable explanation of the object(s) observed.

STATUS: Unknown