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. The document became famous after its existence was revealed in 1947, and would go down in history as the "Oslo Report". 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.