http://www.onwar.com/chrono/1939/nov39/f18nov39.htm
Germans drop mines in British waters
Saturday, November 18, 1939 www.onwar.com
In Britain... German planes parachute magnetic mines into British coastal waters for the first time. Four merchant ships are sunk by magnetic mines off the eastern coast. Meanwhile, IRA activists detonate 4 small bombs in London business premises in Piccadilly.
In the North Sea... The Dutch liner Simon Bolivar is sunk by a German magnetic mine with 86 killed of about 400 passengers and crew aboard.
In Holland... Public opinion is outraged because the mine which sunk the Simon Bolivar was in a major traffic lane. International law requires notification of any such mine-laying.
Looks like its time to start degaussing some ships. Or we could always sell the Germans the detonators from the Mark 14 torpedo for their mines.