German minesweepers active in the North and Baltic Sea according to a report of the American Naval Attaché at Berlin, Germany Nr. R562 dated 15 September 1939

Diary note dated Friday 8 September 1939. An item reported that the German navy was sweeping mines in the North and Baltic Seas and that a Polish coastal battery, presumably at Gdynia, was shooting at the minesweepers although with no success.

Source

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