The US got a full report on this which Ruppelt saw and summarized. The summary was in Hynek's files now at CUFOS. It contains some fact which were not in records the British have uncovered.
4. 16 January 1947 - The North Sea Incident
On the evening of 16 January 1947 Flight Lieutenant David Richards was a senior controller and 2nd in Command of the filter room of RAF No. 11 Group, Bentley Priory. This was situated in the grounds of Hill House, a large Victorian mansion at Stanmore, northwest of London. A Bullseye exercise was in progress, involving mosquitoes of 25 and 29 Squadrons, from RAF West Malling in Kent. Two aircraft from 29 Squadron were operating off the East Coast under the control of the GCI at Trimley Heath, near Felixstowe, Suffolk. GCIs reported to 11 Group Operations Room at Uxbridge, who 'told' their plots to the Filter Room at Stanmore. The first clue that something unusual had happened came when Richards received a call on a landline. He recalled:
"Trimley came up on my direct phone to report a strange plot which was either stationary at a great height or moving erratically at a great speed and then stopping again. If this was a conventional aircraft it would have travelled in a straight line, but it did not do that. This was not an aircraft, it was something very odd. 400 mph [quoted in the Daily Mail] is a pretty disappointing figure, as it is within the range of some 1947 aircraft types. Somebody – either at one of the [radar] stations or at Uxbridge [11 Group Operations Room] – had computed speed between the rather intermittent plots and had come up with a startling figure of 1,000 mph." 
A speed of 1,000 mph was truly startling, for it was not until October 1947 that US test pilot Chuck Yeager first broke the sound barrier (760 mph/1,220 kph at sea level) in a Bell X-1 rocket plane. Richards continues:
"This [estimated speed] emphasises that the thing did not appear to move in a straight course, but faded and reappeared and sometimes stood still, before fading again. Without visual identification – there was none – it would be impossible for the [crew] to be certain it was investigating the same object. Note that it [the Mosquito] carried out an interception on a Lancaster during the 40 minutes between. In this time, at even 400 mph a straight course would take the aircraft from the East Coast to Scotland! I can recall this question of plot identification arising in conversations between us, our stations and Uxbridge at the time. They [Trimley Heath GCI] were looking at the tube and could judge if the echoes were the same object or a new one. This probably gave rise to the estimated speed, based on reappearances in a different place and a different height. Trimley were interrogated on this both by ourselves and Uxbridge, but stuck to their guns. After some talk between Uxbridge and the scientific officers at the stations making the observation on the validity of their plots, not a meteorological balloon etc (which I had already done), it was decided to [divert] a Mossie to investigate." 
If the target was a plane, it was displaying unheard of flight characteristics. Yet if it wasn't a plane, what could it be?
Flight Lieutenant Easterling was also present at HQ No 11 Group when the incident began. He recalls the initial radar track occurred somewhere above the Dutch islands before it was acquired by the GCI. "It came across towards us during the course of an hour or so, stopping and starting, towards Norfolk where it crossed the coastline towards Lincolnshire. Mossies were the only aircraft we had that could reach that height with oxygen." David Richards corroborates this impression. He said that since initial contact was made near the Dutch coast "the object was almost certainly detected by our Chain Home stations. These did not normally operate overland and only looked seaward."
Details of the incident which followed have been preserved in the RAF operations record books (ORBs). ORBs were the logbooks compiled by RAF stations and squadrons to record daily and monthly activities, including everything from sporting events to exercises and operations. During the Cold War, security restrictions meant that few, if any, entries were made in ORBs that refer specifically to investigations of "unidentified" radar tracks. For this reason, the records for 1947 are unique as they allow us to reconstruct how the RAF reacted when confronted by the unknown.
The ORB of Eastern Fighter Sector HQ, RAF Horsham St. Faith (Norfolk), dated 16 January 1947, reveals:
'An unidentified aircraft had been plotted in WC 9585 at 38,000 ft., and Eastern Sector Ops were requested by Group to scramble a Mosquito of 23 Sqdn. to intercept. However, as there was no aircraft available with oxygen this was impossible, and Sector Ops were informed by 12 Group that an aircraft of 11 Group which was already airborne on a Bullseye exercise would try to intercept under Trimley Heath Control.' 
The original tracking placed the target at 38,000 feet moving on a westerly course across the North Sea. According to an Air Ministry memorandum to the US Army Air Force, the incident began 50 miles from the Dutch coast at 52' 52" N 02' 37" E. Later contacts involving Trimley Heath GCI, occurred at lower altitude, placing the "blip" level with the bombers participating in the Bullseye exercise. At Trimley Heath the station's operations log recorded how Mosquito call-sign HAIROIL 27 made an initial contact with an "unidentified" target at 2014 hours when at 17,000 feet but soon lost it. Whilst searching for the target the navigator then picked up a Lancaster or a Lincoln on his airborne radar before GCI guided him towards the "unidentified" target, whereupon:
'five other contacts [were] obtained in quick succession on X. 362 (OPERATION CHARLIE) which was chased from 2120 hours until 2202 hours when interception was abandoned due to A.I. [airborne radar] trouble. This target was completely unidentified. Height at the commencement of the interception was 17,000 feet and target descended to 6,000 feet by 2202 hours.' 
A brief summary of the incident appears in HQ No 11 Group Fighter Command Operations book, which reads:
'...two aircraft operating off the East Coast under Trimley Heath G.C.I. obtained 5 contacts and 5 kills on Lancasters between 15,000 and 18,000 feet...One of these aircraft chased an unidentified aircraft between 2130 and 2200 hours from 22,000 to 5,000 feet. No visual was obtained.' 
The report to the US Army Air Force, attributed to "Air Ministry, Great Britain" summarises the incident as follows:
'During normal night-flying practice at 2230 hours one of British Mosquitos was vectored on to an unidentified A/C at 22,000 ft. A long chase ensued commencing over the North Sea about 50 miles from the Dutch Coast and ending at 2300 hours over Norfolk. Two brief AI contacts were made but faded quickly. The unidentified aircraft appeared to take efficient controlled evasive action.' 
"Evasive action" implies intelligent control and this incident raised fears that an enemy aircraft had intruded upon the exercise. However, it quickly became apparent that no Soviet aircraft could match the performance displayed by this "flying object".
The incident was also linked to another "X raid" tracked by radar earlier that same day. Shortly after 12 noon, Meteors of 74 and 245 Squadrons from RAF Horsham St. Faith were involved in interception practice under the control of the GCI at RAF Neatishead when an unidentified target was tracked at 30,000 feet over Norfolk. The Commanding Officer of 74 Squadron, Squadron Leader Cooksey was asked to divert and intercept but was unable to follow the target due to lack of fuel. Meteor call-sign Kremlin 34 was scrambled but "the aircraft disappeared out of range to the North of [Neatishead]." 
Flt Lt Richards recalled the concern which followed at the Air Ministry and he was ordered to write "a confidential report" on the incident copied to HQ Fighter Command.
"I would assume that the account of the Filter Room picture would have been included in a fuller report from 11 Group which would include similar reports – probably confidential and not included in the ORBs from the GCIs." In summary, Richards said:
"The event has always stuck in my memory as my only 'encounter of the third kind' and although the term 'UFO' was not in use then, we wondered if the wily Russians had produced some secret aircraft from a rapid development of German technology which we in the RAF were beginning to realise was so far ahead of our own." 
Six months later, in July 1947 the FBI agreed to help the USAAF's embryonic study of "flying disks" that would became Project Sign. One of a number of unexplained incidents forwarded to the bureau was a copy of the brief Air Ministry memo concerning the North Sea incident.  The Air Ministry case summary stated that: "no explanation has been forthcoming, nor has it been repeated."This information was not entirely accurate, because a very similar incident had occurred just 24 hours after the North Sea incident. As a direct result, Fighter Command immediately extended its night radar watch. All stations were on alert to watch for the reappearance of "Charlie".
5. 17 January 1947: Operation Charlie Phase 2
On the afternoon of 17 January two Chain Home Low stations in Lincolnshire (Skendleby and Humberstone) tracked what they described as "an exceptionally good track" (U294) at 10,000 feet above the North Sea. With Eastern Sector on alert, Meteor jets from 245 Squadron were placed on standby to scramble if Charlie came within range, but the plot faded from their screens. At 1945 hours the radar station at Humberstone, near Grimsby again tracked an unidentified target over the sea for a period of 30 minutes at a speed of more than 200 mph. The station log records:
'U. 306 [unidentified plot] was followed continuously for 90 miles at 10,000 feet, moving east to west over the North Sea before changing direction towards the south, moving once again across the Wash towards the Norfolk coast.' 
The tension can be measured by an entry that says this was "the longest watch period ever experienced since the termination of hostilities, operational six and a half hours being released at 01.30 hrs".
By the evening, Mosquitoes from 23 Squadron were on "stand by" for the return of Charlie under the control of RAF Neatishead. Situated in the Norfolk Broads, Neatishead is the oldest operational radar station in the world. It began life in 1941 and became a GCI radar station the following year. In his station log, Squadron Leader S. L. Cruwys, reported how on 17 January one mosquito from 23 Squadron had been "scrambled just before midnight to intercept an unidentified high flying aircraft." Cruwys records how an attempt was made to close when contact was made at 18,000 feet but "the observer was unable to hold it as the target was jerking violently".  Further contacts were obtained as the target fell rapidly to 2,000 feet, when both the blip and the mosquito disappeared below radar coverage.
The logbook of Eastern Sector HQ, adds further details:
'One Mosquito of No. 23 Sqdn, pilot F/L Kent, was at readiness at Wittering to attempt interception of the unidentified aircraft which has been plotted several times lately. At 2040 hrs the Bogey was plotted in WN 6038 [grid square]. The plot was at one time heading south and the Mosquito which had been brought to standby was returned to Readiness, but when the plot again headed into Eastern Sector area the Mosquito was scrambled at 2327 hrs. Although getting within 1-2 miles several times, no interception was made on the target which took violent evasive action. The plot faded at 0015 hrs and after patrolling on a North-South line for some time the aircraft returned to base at 0045 hrs.' 
The pilot of the Mosquito was a Sheffield-born World War II night-fighter veteran, William Kent. His log book confirms the incident, with a red ink entry recording an unusual night sortie of 1 hour, 45 minutes – "a scramble interception". In 2001 we were able to trace and interview Kent, who retired from the RAF at the rank of Group Captain.
He recalled the incident clearly:
"I, being one of the very few pilots with any wartime experience and therefore having some understanding of the request, yelled for my navigator and the duty ground crew and leapt off the ground in under four minutes. On a 'scramble' we never listen to any briefings on the ops phone – speed in the air is paramount – and so I had no idea what was brewing until, climbing to height and taken over by the close controller, I was given a brisk brief on the R/T [radio telegraph]. The ORB record is correct except that on reflection with hindsight the unidentified 'aircraft' was almost certainly not an aircraft. It lost height as stated and the airborne radar contact was far more difficult to establish and hold with the aircraft in descent pointing towards the ground. The navigator's screen became swamped with ground returns and the blip was in amongst the cluttered screen, somewhere..." 
Kent's encounter with "Charlie" over East Anglia continued for 20 minutes as the ground controller supplied instructions and the navigator tried to capture the object on the Mosquito's radar.
"At no time at any height despite sporadic radar contacts did I sight anything visually, but on a dark night closing on a target at a speed of 10-20 knots [11-23 mph], extreme care is needed to avoid colliding and then only by steering a few degrees off centre does one's night vision show a darker silhouette – often frighteningly close!"
After losing the "blip," the adventure ended and Kent continued to patrol the area without further success. The following day he discussed the incident with the Neatishead fighter controller and a report was sent to the commanding officer of 12 Group. They decided that the "unidentified aircraft" was, most probably, a leaking meteorological balloon. The radar target, if this theory was correct, would have been produced by reflections from metal cannisters as the balloon dropped towards the ground. "The report, which I saw, had no comment except a margin sketch of a pricked balloon," Kent recalled.
Kent's scepticism was typical of the RAF's pragmatic attitude both to the "ghost plane" and, in later years, towards the flying saucer enigma. Nevertheless, the intrusions continued and Charlie appeared again on the night of 23 January whilst three senior officers from the Central Fighter Establishment were visiting RAF Neatishead to control an interception exercise. This was cancelled when "an unidentified high altitude aircraft" appeared on the GCI radar at 28,000 foot. Mosquitoes from 23 Squadron, who in normal circumstances would have been scrambled were unavailable as they were moving to RAF Coltishall. The nearest available aircraft, Mosquitoes of 264 Squadron from RAF Linton-on-Ouse in Yorkshire, were scrambled but before they could reach the Norfolk coast Charlie had faded from the radar screen.  During the alert, Eastern Sector turned for help from 74 Squadron's Meteors and Flight Lieutenant Lawrence was scrambled "to intercept an unidentified aircraft out to sea." The 'aircraft' disappeared before an interception was possible and with the weather closing in, Lawrence's Meteor suffered severe icing and was forced to return to Horsham St Faith. 
6. The Air Ministry Investigation
This was the third occasion that unidentified flying objects had been tracked by stations defending England's east coast and the third time that interception attempts had ended in failure. On each occasion the mysterious blips came in over the North Sea towards Norfolk before descending from great height and disappearing beneath radar cover. Concern was mounting and the ORBs record how, as a direct result of the incidents on 23 January, Flying Officer Sewart of HQ Northern Signals Area spent six days at RAF Neatishead on a special mission to investigate the mysterious events. F/O Sewart's assignment was to produce a report "on the unidentified high flying aircraft that have been plotted in recent months." 
Sewart's report was completed on 27 January 1947 but is missing from the Public Record Office file where it is listed as an attachment to the station logbook. Summarising its contents, Squadron Leader Cruwys said 'evidence appears to be strong' that the unidentified tracks were caused by radio-sonde balloons released from Downham Market in Norfolk. Downham was a World War Two bomber airfield that was used by the USAAF's 8th Weather Squadron in 1947 for the release of balloons for the study of the upper atmosphere. It can be inferred, in the absence of his original report, that Sewart had matched the release of radio-sondes with Charlie's movements. He may have decided that balloons trapped by turbulent upper-air currents that were developing over southern England had been blown back towards their launch station in Norfolk. Their movements whilst trapped in upper air currents had taken radar operators by surprise and had led to the scramble of aircraft.
However statements made by the Air Ministry, firstly to the Press in April 1947 and again to the USAAF in July, flatly contradict Sewart's conclusions and imply that the Air Staff remained open-minded about the identity of Charlie. Even Group Captain Kent's account of the 'unidentified aircraft' ended with this comment: "I mentioned that a burst met balloon was a possibility, deduced afterwards from its 'behaviour'...but at that time these things [flying saucers] were unheard of and not taken at all seriously." 
Other expert opinion attributed the unusual radar blips to freak weather conditions. Operation Charlie coincided with the arrival on 24 January 1947 of a deep cold weather front over southern England, a fact that did not escape attention at the Air Ministry. Before the 1950s, knowledge of the role played by freak weather conditions in the production of "false" echoes nick-named "angels" was in its infancy. Although little understood at the time, the astronomer Dr J. Allen Hynek, who was employed as a consultant to the US Air Force Project Blue Book, believed "atmospheric inversion effects" were the most likely explanation for the English "ghost plane" reports.  This explanation is challenged in a technical assessment of the evidence by Martin Shough (see Appendix).
The Air Ministry may have decided it could dismiss the majority of the mysterious blips on its screens as balloons, but in July when the US authorities began to investigate reports of "flying saucers," the RAF continued to list the North Sea incident as "unexplained". Dr Hynek's notes on this case read: "The object observed here was obviously not astronomical. From the information given, it appears that this was definitely an aircraft..."  This raises an obvious question: if it was an aircraft, then where was it from?
According to Geoff Easterling the RAF's prime suspect was a Russian intruder aircraft flying from a base in occupied Germany. However, if the speed and performance of the target tracked on 16 January 1947 recalled by David Richards (and apparently confirmed by the contemporary press reports) are correct, this becomes an unlikely proposition. Soviet aircraft were unreliable at long range, and it seems inconceivable that an intruder mission would risk an overflight of UK territory in such a reckless fashion during a period of extreme and unpredictable weather. In addition, Soviet versions of the US B-25 were capable of a maximum speed of 250-300 kts, a figure well within the interception ratio of the RAF Mosquito.
It remains unclear if further unidentified radar blips continued to plague the RAF as the "ghost plane" era moved into the age of the "flying saucer." Entries in the logbooks of radar stations on the south coast of England describe a number of similar incidents during April and May, 1947. One entry from the logbook of RAF Rye, a CH station in Kent, reads: "...the most noteworthy track plotted was an unidentified aircraft which was plotted from 52 miles out to the maximum range of 186 miles." 
Group Captain Kent recalls: "I have no other sorties listed in my log books as 'scramble intercepts' such as that of 17 January 1947, but I did fly a few others against 'odd' and 'strange' blips as seen by ground radars in an around East Anglia. I flew at least one in daylight but nothing was seen." 
When rumours concerning the panic of January 1947 leaked to the national newspapers in April the Air Ministry decided to deny all knowledge. A spokesman told the Daily Telegraph they were taking no further action. 'We have found no evidence to support the reports at all,' he said. The Yorkshire Post was less inclined to dismiss the mystery completely and its editorial looked at the problem from a different angle:
Radar has plotted some strange things in its time, from children's kites and raindrops to formations of geese. But it surely never plotted a stranger thing than this. What is the aircraft? Speculation takes us into those regions where the scenes are laid for so many thrilling stories in the boys' magazine. Is it a diamond or drug smuggler? Is it conveying a secret agent from one foreign Power to another? In that event it would of course have the secret papers and probably also a beautiful woman spy on board. Is it a guided missile?
The newspaper compared the ghost plane mystery with the reports of phantom German Zeppelins that had circulated before the outbreak of World War I and observed: "It seems to be established that it is only at times of peculiar stress that the public is in the psychological state to receive and circulate such stories." The practical steps to solve the mystery were clear: "Fast RAF fighters must continue trying to intercept the visitor if it should return. Our air service has the fastest fighters in the world and should not find it impossibly difficult – meanwhile we may enjoy the atmosphere of mystery and imagination which surrounds the ghost aircraft." 
The most intriguing reference to Operation Charlie is found not in the pages of a newspaper, but in the memoirs of the one-time head of Project Blue Book, Captain Edward Ruppelt. In his book The Report on Unidentified Flying Objects, published in 1956, the retired officer devoted several pages to a description of an intelligence briefing document drawn up by Project Sign staff early in 1948. This was the legendary "Estimate of the Situation" which listed a number of unexplained sightings and concluded that the most probable explanation "was that they [flying saucers] were interplanetary." The estimate travelled upwards to the highest echelons of the US Air Force where the Chief of Staff, General Hoyt S. Vandenberg, batted it back. "The general wouldn't buy interplanetary vehicles [and] the report lacked proof," wrote Ruppelt. "Some months later it was completely declassified and relegated to the incinerator." 
Controversy has surrounded the status of the Estimate ever since Ruppelt wrote these words. Not one single copy appears to have survived, and some have suggested it never existed. However, Ruppelt describes reading one copy that had escaped destruction, and he described it as "a rather thick document with a black cover... stamped across the front were the words TOP SECRET." Included in the Estimate was a collection of UFO reports that preceded Kenneth Arnold's sighting of 24 June 1947. The report's authors used these to support their interplanetary theory, arguing that pre-Arnold sightings could not be dismissed as hype or rumour triggered off by media stories. Among the cases used to prove this point were "the English 'ghost airplanes' that had been picked up on radar early in 1947." 
This investigation into the British records has established that six months before Kenneth Arnold's sighting, the RAF had logged its first official report of an "unidentified flying object." Furthermore, by July 1947 when the first sightings of "flying saucers" were made in the USA, the Air Ministry remained unable to explain the intruder it had logged in January of that year. This implies that an exchange of intelligence on "unidentified flying objects" between the USA and UK began in 1946-47 with the ghost rocket and ghost planes. Cold War historian Richard Aldrich writes that air power was the cutting-edge of post-war strategy "and it was appropriate that Anglo-American air intelligence was in turn the cutting edge of Western intelligence co-operation." 
Air Intelligence files relating to "Operation Charlie" cannot be traced at the Public Record Office or the RAF Air Historical Branch at Bentley Priory. However, documents at the US National Archive show the Air Ministry's Assistant Chief of Air Staff (Intelligence), Air Vice Marshal Sir Thomas Elmhirst, working closely with his opposite number in the US Army Air Force (General George McDonald) during the "ghost rocket" alarm in 1946. Whilst the Swedes were asking the RAF "to take all possible measures to prevent the Americans finding out about Swedish full co-operation in investigating the mysterious missiles," Elmhirst was discreetly passing all intelligence on the subject to McDonald in Washington.  Given the level of co-operation that existed between the allies post-war, we can be confident that a dossier on what Ruppelt called "the English ghost planes" (Operation Charlie) would have been shared at the highest level with the Americans when Project Sign was created. What the study contained and concluded remains a mystery.