British merchant ships warned to keep away from the Black Sea according to a letter of the German naval attaché dated 26 September 1939

In his letter dated Istanbul, Turkey 26 September 1939 No. 60g.Kdos reported the German naval attaché to the Oberkommando der Kriegsmarine at Berlin that the radio message warning the British merchant shipping about visiting the Black Sea and to leave the Danube harbours was in local British shipping circles still not confirmed.

Source

Bundesarchiv. German Marineattaché for Turkey, Greece, Romania and Bulgaria 1939-1941. RM 12-II/459.