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.
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 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.
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.
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 "Hullo, hier ist London".
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.
[1] 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.
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.
[Radio Direction Finding, the British name for radar] 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.
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.
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.
The mentioned size of 80 cm (31.5 in)-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 76 mm (3 in).
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.
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.
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 mentions that the British air raid on Wilhelmshaven in September 1939 was detected while the aircraft were 120 km (75 mi) from the German coast using radar.
On 12 February 1947, Jones gave a talk to the Royal United Services Institute that publicly revealed for the first time the existence and importance of the Oslo Report.
[8] It [the Oslo Report] told us that the Germans had two kinds of radar equipment, that large rockets were being developed, that there was an important experimental establishment at Peenemünde and that rocket-driven glider bombs were being tried there.
Jones revealed some of the Report's contents, holding back many details to test anyone claiming authorship but neither Henry Cobden Turner nor Mayer heard of the talk at the time.
On 15 December 1953 the dinner was arranged, during which one of Jones' friends, Professor Frederick Norman of King's College London, excitedly shouted "Oslo!!".