The Oslo Report

At the beginning of November 1939 two anonymous packages reached the British legation in Oslo, the capital of neutral Norway. In the first an unknown German asked whether the British wished to learn the secrets of German armaments. The second, sent after an agreed signal, contained a seven-page typescript in German and a small vacuum tube from an experimental fuze. The document, later called the Oslo Report, described German radars, radio guidance systems for bombers, remote-controlled missiles, new torpedoes and fuzes, as well as the experimental establishments at Peenemünde and Rechlin. In London many took it for a German plant. A young physicist assigned to scientific intelligence, Reginald Victor Jones, believed it was genuine and throughout the war checked which of its predictions were coming true. Its author was Hans Ferdinand Mayer, director of the research laboratory of the Siemens & Halske concern in Berlin. His name was made public only in 1989, nine years after his death.

Chronologies spread the affair over three days: on 1–2 November Mayer writes the report, on 4 November he sends a letter to the naval attaché, and on 5 November he sends the report. This version needs several corrections: the attaché’s name was Hector Boyes, not “Boyer”; Britain had a legation in Oslo, not an embassy; and 4 November was the day the letter reached Boyes, not the day it was sent.

Hans Ferdinand Mayer

Hans Ferdinand Mayer was born in 1895 in Pforzheim into a family of modest means. In 1914 he volunteered for the army and on his nineteenth birthday, 23 October 1914, was seriously wounded. After the war he studied mathematics, physics and astronomy at Karlsruhe and Heidelberg, where in 1920 he took his doctorate under the Nobel laureate Philipp Lenard, later an ardent supporter of Hitler and champion of so-called “German physics”. In 1922 he joined the Siemens & Halske laboratory in Berlin and turned to telecommunications, in particular the transmission of signals by cable over long distances. In 1926 he published the theorem of the equivalent current source, formulated independently by the American Edward Norton; in electrical engineering textbooks it is known as Norton’s theorem, and in Germany also as the Mayer–Norton theorem. In 1936 Mayer became head of the concern’s central research laboratory, and in 1938 its director.

Siemens was one of the great German concerns that worked for all three armed services. The head of its laboratory kept in touch with other firms and with military establishments, heard about many programmes and travelled around Europe on business. Mayer was an opponent of National Socialism. According to the accounts he later gave his family, Germany’s attack on Poland on 1 September 1939 convinced him that Hitler’s enemies had to be helped, and he decided to pass on to the British everything he knew about German military technology. The opportunity came with a business trip to Scandinavia planned for the turn of October and November.

Oslo, 1–5 November 1939

Mayer arrived in Oslo on 30 October 1939 and took a room at the Hotel Bristol. Norway was neutral, and the British legation lay a quarter of an hour’s walk from the hotel. Mayer judged, however, that a personal visit was too dangerous: the legations of the belligerent states were watched, and a German entering a British mission would attract attention. He borrowed the hotel’s typewriter from the porter and over two days, 1 and 2 November, wrote his report. He wrote in German, without company letterheads and without names. He signed himself “a German scientist who wishes you well”.

First he sent a letter asking whether the British were interested in information about current and future German weapons. If so, they were to give a sign by radio: at an agreed time the BBC German-language broadcast was to open not with the usual announcement but with the words “Hullo, hier ist London”. According to most accounts Mayer posted this letter on 1 November, and it reached the British naval attaché in Oslo on 4 November. Some chronologies give 4 November as the day the letter was sent, but that is the date it was received. The attaché was Hector Boyes (in some lists wrongly spelt “Boyer”), a retired Royal Navy rear admiral who had returned to service as attaché with the rank of captain. There is sometimes talk of a British embassy, but at the time Britain had a legation in Norway, headed by the minister Cecil Dormer. The message about the signal was passed to London, and the BBC changed its announcement as the stranger had asked. The BBC World Service is also sometimes mentioned; in 1939 this was the German service, broadcast as part of the BBC’s European programmes.

The second package contained the report itself and proof of its credibility: a vacuum tube from a prototype proximity fuze for anti-aircraft shells. According to the German literature and some British accounts, the report reached the legation on 5 November. Mayer himself later said that he posted the two letters on successive days. Some British accounts, however, among them the Military Intelligence Museum, say that the report arrived about a week after the signal was broadcast. In any case the dates 1–5 November are the most widely accepted, and according to some researchers copies of the report with a translation and drawings were sent to London as early as 6 November.

Mayer did not stop at the report. He also wrote to his old friend, the English engineer Henry Cobden Turner, proposing that they correspond through a mutual acquaintance in neutral Denmark, Niels Holmblad. From Oslo he went on to Copenhagen, arranged this with Holmblad and returned to Germany. The channel ceased to work on 9 April 1940, when the Germans occupied Denmark.

What the report contained

Boyes saw at once that the document might be important. He had it translated by a member of the legation staff and sent it to London, to British intelligence, the Secret Intelligence Service (MI6), and to naval intelligence. The original was retyped with copies for circulation; one copy of the German text survives to this day, without the drawings Mayer most likely enclosed. The report consisted of several short chapters. Some of the information Mayer knew only at second hand, and that part proved wrong, but most of it concerned electronics he knew at first hand.

The first chapter dealt with the Junkers Ju 88 bomber, which was supposedly being built at a rate of some 5,000 a month, so that by April 1940 the Luftwaffe would have 25,000–30,000 of them. This was a vast exaggeration: about 15,000 Ju 88s were built in the whole war. The aircraft itself, however, was real, and the British already knew it from combat: on 16 October Ju 88s had attacked warships in the Firth of Forth. Mayer also wrote of an aircraft carrier, the Franken, due to be ready at Kiel in April 1940. He most probably confused the second carrier, whose construction had been halted in September 1939, with the tanker Franken, which was being built next to the carrier Graf Zeppelin.

The report went on to describe remote-controlled gliders carrying explosives, with a span of about three metres and a rocket motor for the final phase of flight, tested at Peenemünde; they resembled later guided missiles such as the Henschel Hs 293. It mentioned an autopilot allowing an aircraft to be flown without a pilot, and remote-controlled, gyroscopically stabilised rocket projectiles of 80 cm calibre. Peenemünde itself, on the island of Usedom on the Baltic, was presented as an important experimental establishment. To British rocket specialists, who were then thinking of small solid-fuel projectiles, that figure seemed absurd. After the war it could be recognised as one of the projects of Wernher von Braun’s team; Mayer simply did not know that the Germans were using liquid fuel. Mayer named Rechlin, on Lake Müritz, as the Luftwaffe’s main experimental establishment, “worth attacking”. He also described the method used to take Polish bunkers in September 1939: smoke shells forced the garrison to retreat deeper inside, and under cover of the smoke soldiers with flamethrowers moved in.

The most valuable chapters were those on electronics. Mayer wrote that the British raid on Wilhelmshaven in September 1939 had been detected while the aircraft were still 120 kilometres from the coast, by devices that sent out short pulses of radio waves and measured the time taken for the echo to return. He gave the power of the transmitters, the duration of the pulses and the range, and even suggested ways of jamming them. The one thing he did not know was the most important: the wavelength. He added that by April 1940 these stations were to be set up along the coast, and that work was under way on a second system using waves 50 cm long. This was a description of German early-warning radar, such as Freya, and of the decimetric radars from which the gun-laying and night-fighter radars later developed. He also described a device being developed at Rechlin which measured by radio the distance of a bomber from a ground transmitter, on a wavelength of about 6 metres. This was an early version of the system the Luftwaffe introduced in 1940–1941 as Y-Gerät.

The chapter on torpedoes described two new types. One was to be guided by radio to the vicinity of a convoy, and over the last few hundred metres by two microphones in the warhead that picked up the noise of a ship’s propellers. The other had a magnetic pistol that exploded beneath a ship’s keel when the steel hull altered the Earth’s magnetic field. Mayer claimed that the Royal Oak had been sunk by such a torpedo, explained how the pistol worked and suggested that it could be countered by generating a suitable magnetic field. The Germans used the same principle in the ground mines that since September had been sinking ships off the British coast.

The last chapter concerned fuzes. Mayer wrote that in artillery shells mechanical fuzes were giving way to electrical ones; he described electrical time fuzes and the idea of a proximity fuze that would detonate when the shell came close to its target, such as an aircraft. The enclosed tube came from just such a fuze. He named the Rheinmetall works at Sömmerda in Thuringia as the manufacturer. The German capacitive fuze he described proved of little use in practice; effective proximity fuzes were introduced during the war by the Americans and the British.

Distrust in London

In London the report was received with indifference or disbelief. The Admiralty considered it “too good to be true”. The sceptics had concrete arguments: no single man could know so many secrets of all three armed services; the German army, navy and air force were known to be rivals that guarded their own programmes; and the figures for the Ju 88 were obviously exaggerated. The report might therefore be disinformation planted by the Abwehr to convince the British that Germany was technically stronger than it really was. According to Jones, the three service ministries threw their copies away.

The exception was Reginald Victor Jones, a 28-year-old Oxford physicist who since 1936 had worked at the Royal Aircraft Establishment at Farnborough. In September 1939 the Air Ministry attached him to its intelligence branch as the first scientist in the history of the British intelligence services. His task was to investigate new German weapons, real and rumoured. The Oslo Report was passed to him by Frederick Winterbotham, head of the air section of MI6. Jones is sometimes described as Assistant Director of Intelligence at the Air Ministry, but he took up that post, with the suffix “Science”, only later in the war; in the autumn of 1939 he was a young scientist with no standing in the hierarchy. Jones noted that although the report mixed solid information with rumour, the parts dealing with electronics were technically coherent and consistent with what the British themselves knew about radar. He concluded that the author was competent and that his knowledge came from work in the electrical industry, which supplied equipment to all the services. In a report of 1940 he wrote that only two explanations were possible: either it was a plant intended to convince the British that the Germans were as advanced as they were, or the source had genuinely turned against Germany and wanted to pass on everything he knew. The second possibility was supported by the general accuracy of the information, by the fact that the fuze had been enclosed without any demands in return, and by the author’s making no attempt to gain anything from the affair.

Jones kept his copy and, as he recalled after the war, “in the few dull moments of the war” he would look up the report to see what else was coming. After the war he called it “probably the best single report received from any source during the war”.

The author’s secret

The British did not know who the author was, and the Germans never learned of the report’s existence. Mayer, however, ran into trouble for another reason. In 1943 the Gestapo arrested him for listening to foreign radio stations, the BBC among them, and for criticising the regime. Thanks to the intervention of the Siemens management and, according to some accounts, of his former supervisor Lenard, he escaped trial before the People’s Court, which could have ended in a death sentence. Until the end of the war he was a prisoner in concentration camps, among them Dachau and Sachsenhausen. At Dachau he ran a radio engineering laboratory in which prisoners from twelve countries worked, among them Kazimierz Drewnowski, former rector of the Warsaw University of Technology.

After the war Mayer went to the United States, where he worked in the military aviation laboratories at Dayton and then taught at Cornell University. In 1950 he returned to Germany and until 1962 headed Siemens’s telecommunications research department in Munich. Jones revealed the existence of the report in a lecture in London on 12 February 1947, without knowing who its author was. In 1953 he met Henry Turner by chance, and Turner told him about a letter from a friend in Oslo. In 1955 Jones met Mayer in Munich and satisfied himself that he was the man. The two agreed to keep the secret so as not to expose Mayer and his family to accusations of treason. Mayer told his family that he was the author of the report only in 1977, stipulating that the matter be revealed after his own death and that of his wife. He died in 1980. Jones gave his name in a book published in 1989.

Significance

The Oslo Report did not change the course of the war at a stroke, nor could it have done, since in November 1939 hardly anyone in London believed in it. Its value emerged gradually as one prediction after another came true. It gave Jones and his small team a map of what to look for, and the conviction that the Germans had radar similar to Britain’s. In the summer of 1940, when Jones uncovered the German bomber guidance system Knickebein (PL), and then further radio systems, including the one described in Oslo, the so-called Battle of the Beams began: the British jammed and distorted the German radio beams, and some of the bombs meant for cities fell on fields instead. This struggle was fought in the background of the Battle of Britain and the night raids on Britain in 1940–1941.

Knowledge of German radars working on a wavelength of about 50 cm later helped to prepare the simplest countermeasure: strips of aluminium foil of the right length, dropped from bombers. The British called them Window; in modern terminology they are known as chaff. They were first used in July 1943 during Operation Gomorrah, the raids on Hamburg. The name Peenemünde, mentioned in the report, reappeared in intelligence reports in 1942–1943, when the British were searching for the site where the Germans were building V-2 rockets; in August 1943 the RAF bombed it in a great night raid. Acoustic torpedoes, remote-controlled air-launched missiles and proximity fuzes came into service in 1943–1944.

The Oslo Report affair showed how important technology had become in this war and how few people on either side understood it. It also shaped British scientific intelligence, which in the following years combined information from agents, decrypted Enigma messages, aerial photographs and the interrogation of prisoners, and whose head was none other than Jones. Finally, the report is one of the earliest examples of German resistance to Hitler that took the form of neither a conspiracy nor an assassination attempt: a lone engineer, devoted to his country but not to its rulers, decided in the first weeks of the war that he must help to bring down Hitler’s regime, and did so without any gain for himself.