New minefield laid in the North Sea according to a report of the American Naval Attaché at Berlin, Germany Nr. R562 dated 15 September 1939

Diary note datedMonday 4 September 1939. An item reported that according to the Foreign Office a mine field was laid in the North Sea with as postions latitude 53.36 and56.30 North and longitude 4.25 and 6.02 East.

Source

National Archives. FDR Presidential Library&Museum Roosevelt PSFC000175. War diary Naval Attaché Berlin, volume 1 (1 September 1939-26 May 1940)