One of the most important pieces of military intelligence throughout the entire Second World War arrived through a surprising channel. An anonymous report was received in neutral Norway offering to share German military secrets. This would become known as the Oslo Report and its contents would be some of the most underappreciated, but vital, of the war.

The report was written by Hans Ferdinand Mayer, a German mathematician, physicist and businessman who had decided to leak military secrets to the British in order to aid in the defeat of the Nazis. Due to his position as the director of the telecommunications research laboratory for the large industrial company Siemens, he had access to a large amount of military information through the contracts the company maintained. In late October 1939, Mayer travelled to Oslo, Norway for a supposed business trip and from his hotel room, started to write the seven page report. On the 4th November, the British Naval Attache at Oslo, Captain Hector Boyes, received an anonymous letter with the offer of German military secrets. If he wished to receive them, the BBC World Service German service was to change its introduction to ‘Hullo, hier ist London.’ After some deliberation the change was made and a week later the report was delivered, along with a prototype for a proximity fuse. Recognising the potential importance of this report, Boyes ordered a translation made which he sent to MI6 along with the original due to the technical drawings included by Mayer.

The report was received with disbelief in London, who thought of it as a hoax crafted by the Abwehr (German Military Intelligence) partly as they could not see how one man would be able to know all this information. However, the report was passed to Dr Jones, the new lead in the Scientific Intelligence department who believed it’s credibility and argued this with his superiors.

The contents of the report focused on numerous areas and while some of the statistics stated were inaccurate it contained vital insight into the German war machine.
Key pieces of information contained in the report are;
- the first references to the German rocket programme situated at Peenemünde, where eventually V1 and V2 rockets would be developed and tested. This would prove a valuable piece of information for future bombing campaigns
- The site of the Luftwaffe’s main research site in the development of new aircraft at Rechlin, Mayer remarked it would make a good target to bomb
- Two new torpedo types in use by the Kreigsmarine, the second of which Mayer described how Allied ships could defeat by eliminating a ship’s magnetic field
- Detailed descriptions of aircraft rangefinders to guide Luftwaffe bombers to their targets for nighttime raids. With these descriptions the British could counteract the guiding transmissions
Most importantly however, was his analysis and drawings of the German early air raid warning system. Mayer described how the British air raid on Wilhelmshaven in September 1939 went disastrously due to radar detecting them 75 miles before they reached the German coast and gave the technical characteristics of how it worked, as well as details to exploit its vulnerabilities. This section of the report really displayed Mayer’s knowledge of radar technology and allowed the development of a countermeasure known as Window, to effectively jam enemy radar, which would be vital to saving the lives of Allied pilots in the air campaign over Germany.

While this report was to be overshadowed by the later cracking of the Enigma code, it still was incredibly significant to the British and Allied war effort and has been called the single most important intelligence report of the entire Second World War. While initially viewed as unreliable, other intelligence gathered would prove time and time again the value of the 1939 Oslo Report.

By Daniel Smith