Several Internet sites state that on the night of 12th/13th November 1939, 4 German Destroyers - Hans Ludemann (Z-18), Hermann Kunne (Z-19), Karl Galster (Z-20), and Wilhelm Heidkamp (Z-21) laid a minefield in the South Edinburgh channel. I have not yet found a primary source for this information, but it seems plausible. The C-in-C Nore’s report at the time states that an enemy minefield is the most likely cause of the incident and cites the observation of two isolated explosions by Adventure and/or Basilisk as evidence for this. The fact that four ships were struck on the same day would also tend to indicate a fairly extensive and newly laid minefield, which would therefore imply surface ship or possibly submarine laid mines.
Hans Ludemann's operations record