The Oslo Report was one of the most spectacular leaks in the history of military intelligence. Written by German mathematician and physicist Hans Ferdinand Mayer on 1 and 2 November 1939 during a business trip to Oslo, Norway, it described several German weapons, some in service and others being developed.
Mayer mailed the Report anonymously in the form of two letters to the British Embassy in Oslo, where they were passed on to MI6 in London for further analysis, providing an invaluable resource to the British in developing counter-measures, especially to navigational and targeting radars and contributed to the British winning the Battle of Britain.
Background Hans Ferdinand Mayer received his doctorate in physics from the University of Heidelberg in 1920. After spending two years as a research associate there in his doctoral supervisor's (Philipp Lenard) laboratory, he joined Siemens AG in 1922. He became interested in telecommunications and joined Siemens' communication research laboratory, becoming its director in 1936. In this position, he had contacts all over Europe and the United States and had access to a wide range of information about electronics development in Germany, especially in the military sector.
Sending the report After Hitler invaded Poland on 1 September 1939, Mayer decided to divulge to the British as much as he could about military secrets to defeat the Nazi regime. He arranged a business trip to Scandinavia in late October 1939, arrived at his first scheduled stop, Oslo, Norway, on 30 October 1939 and checked into the Hotel Bristol. Mayer borrowed a typewriter from the hotel, and typed the seven-page Oslo Report in the form of two letters over two days. He mailed the first on 1 November, asking the British military attaché to arrange for the BBC World Service to alter the introduction to its German-language programme if he wished to receive the Report. This was done, and he sent the Report along with a vacuum tube from a prototype proximity fuze.
He also wrote a letter to his long-time British friend Henry Turner, asking him to communicate with him via their Danish colleague Niels Holmblad. This indirect communication path was required since Britain and Germany were at war, but Denmark was neutral. Mayer continued his travels to Denmark to visit Holmblad, asking if he could relay information between himself and Turner. Holmblad readily agreed, but once Hitler invaded Denmark on 9 April 1940, this communication route was no longer feasible. Mayer then returned to Germany, and was arrested for political offenses by the Gestapo in 1943. He was imprisoned at Dachau and other Nazi concentration camps until the war ended. The Nazis never knew of the Oslo Report.
British reaction On 4 November 1939, Captain Hector Boyes, the Naval Attaché at the British Embassy in Oslo, received an anonymous letter offering him a secret report on the latest German technical developments. To receive the report, he was to arrange for the usual announcement of the BBC World Service's German-language broadcast to be changed to "". This was done and resulted in the delivery of a parcel a week later, which contained a typewritten document and a type of vacuum tube, a sensor for a proximity fuze for shells or bombs. The document became famous after its existence was revealed in 1947 and would go down in history as the "Oslo Report".Hinsley, 1979, pp. 508–512 Boyes quickly appreciated the Report's potential importance and had a member of the embassy staff make a translation which he forwarded to MI6 in London along with the original.
The Oslo Report was received with indifference or even disbelief by British Intelligence, with the notable exception of Dr. R. V. Jones, a young Ph.D. physicist who had recently been put in charge of a new field called "Scientific Intelligence". Jones argued that despite the breadth of information and a few inaccuracies, the technical details were correct and argued that all the electronic systems divulged therein be further explored. In a 1940 report, Jones summarized his thoughts,
The contribution of this source to the present problem may be summarised in the statements that the Germans were bringing into use an R.D.F. system similar to our own,... A careful review of the whole report leaves only two possible conclusions: (1) that it was a "plant" to persuade us that the Germans were as well advanced as ourselves or (2) that the source was genuinely disaffected from Germany, and wished to tell us all he knew. The general accuracy of the information, the gratuitous presentation of the fuse, and the fact that the source made no effort, as far as it is known, to exploit the matter, together with the subsequent course of the war and our recent awakening with Knickebein, weigh heavily in favour of the second conclusion. It seems, then, that the source was reliable, and he was manifestly competent.R.V. Jones. Air Scientific Intelligence Report No. 7, The Edda Revisited, 17 July 1940. Churchill Archives Centre, Cambridge University, Reginald Victor Jones Papers, RVJO B.24
In his 1989 book, Jones summarized the importance of the Oslo Report,
It was probably the best single report received from any source during the war.... Overall, of course, the contributions from other sources such as the Enigma decrypts, aerial photographs, and reports from the Resistance, outweighed the Oslo contribution, but these were all made from organizations involving many, sometimes thousands of individuals and operating throughout most of the war. The Oslo Report, we believed, had been written by a single individual who in one great flash had given us a synoptic glimpse of much of what was foreshadowed in German military electronics.R. V. Jones (1989), p. 275.
While Jones trusted the Oslo Report, the Admiralty thought that the Report was "too good to be true" and was deception by the Abwehr, with its fantastic claims written by psychological warfare experts. An additional argument raised by the doubters was that no person could have such wide knowledge of weapons technology as discussed in the Report. This was mainly because of service rivalry in Britain and the US and it was known that there was similar rivalry in Germany. The Oslo Report is concentrated on electronic technology; several big German companies were involved in such projects for all three armed forces and some scientists in these companies would have had knowledge of much of the research being conducted.
Report contents The original typed report was seven pages long. It was retyped, with a number of carbon copies being made for distribution. No specimen of the original translation is known and the German version held by the Imperial War Museum is one of the carbon copies and lacks the sketches that were apparently included in Mayer's original. A typed copy in German can also be found in the Public Record Office, while the report has been published twice in English translation.Public Record Office, AIR 40/2572.F.H. Hinsley (1979), Appendix 5.R.V. Jones (1989), Appendix A. The section headings given here correspond to those in the report. Some of the information Mayer heard was second-hand and later proved to be incorrect.
Ju 88 programme Junkers Ju 88 medium bomber production levels are stated to be probably 5,000 per month, with a total of over 25,000–30,000 predicted to be produced by April 1940. This turned out to be a huge exaggeration of production levels, as total production of the Ju88 during the entire war was 15,000.
Franken The report states that the German navy's first aircraft carrier is at Kiel, and was expected to be finished in April 1940. The carrier was referred to as Franken. It is sometimes suggested that Mayer was mistaken and that he was instead identifying the carrier Graf Zeppelin. The construction of Graf Zeppelin was well known to Allied navies. Following Kriegsmarine ship naming policy, she was known as "Flugzeugträger A" prior to her launch and naming on 8 December 1938.
A second carrier known as "Flugzeugträger B" was also laid down in Kiel in 1938 with a launch date planned for July 1940, possibly to be named as Peter Strasser. Work on this second carrier was halted in September 1939 and she was broken up the following year. It is possible that Mayer misinterpreted the construction of the large naval tanker Franken for this second aircraft carrier and wanted to alert the Allies to this development.Franken at german-navy.de Retrieved 26 June 2011. The naval tanker (launched on 8 March 1939) was being built next to the Graf Zeppelin, itself still under construction.
Remote-controlled gliders This section of the report described remote-controlled gliders with a wingspan and long, carrying an explosive charge, fitted with an altimeter intended to maintain them at an altitude of above the water, the horizontal stage of their flight to be powered by a rocket motor. This description is similar to the Blohm & Voss BV 143, or if the wingspan alone is considered, it could have referred to the Henschel Hs 293 design, controlled with an FuG 203 Kehl transmitter in the aircraft and an FuG 230 Straßburg receiver in the ordnance.
Autopilot Here, Mayer briefly described another remote-controlled system, this time for an aircraft instead of for a rocket.
Remote-controlled projectiles The German word Geschoss was used in the report, which can be translated to mean artillery shell, but the German text clearly states that a rocket was meant. This is also clear from the remark that the projectile is highly unstable when fired, while artillery shells would be spin-stabilized (or fin-stabilized in the case of mortar projectiles). The mentioned size of -calibre was seen as a curious item at the time; even by 1943, British rocket developers were focused on solid fuels and thinking in diameters of around . A solid fuel rocket of more than ten times this diameter would have caused a credibility gap, which did in fact happen when more information later became available to British intelligence. With hindsight, the description can be recognised as the A8 rocket, which had a diameter of . The crucial item of information omitted by the author of the Oslo Report was the use of liquid fuels in the German ballistic rocket program.
Rechlin Rechlin is a small town on the southern shore of Lake Müritz north of Berlin, with the turf-covered airfield – some north of the 21st century Rechlin–Lärz Airfield – being the core of the Luftwaffe's central Erprobungstelle aviation test facility, first built as a military airfield by the German Empire in August 1918. The facility's main grass airfield, set up in the manner of a pre-WW II aerodrome without clearly defined runways, was bounded by a roughly hexagonal-layout perimeter road that is extant. Mayer noted that the Luftwaffe's laboratories and research centers were there and that it was a "worthwhile point of attack" for bombers.
Methods of attacks on bunkers Mayer noted during the invasion of Poland in 1939, Polish bunkers were attacked using smoke shells which forced their crews to withdraw deeper into the bunkers, following which soldiers armed with flamethrowers attacked under cover of the smoke.
Air raid warning equipment