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.