This was a British naval minelaying operation as part of the creation of the Dover Mine Barrage series of minefields (9/16 September 1939).
The minelaying destroyers Esk and Express departed during the night of 9/10 September to lay offensive minefields in the supposed exits of the lanes through the German defensive minefield. Between 11 and 16 September the minelayers Adventure and Plover, supported by a number of auxiliary vessels, laid 3,000 mines in the Strait of Dover with escort provided by the cruiser Cairo and destroyers of the 19th Destroyer Flotilla. The success of the undertaking is attested by the German loss of U-12 on 8 October, and U-16 and U-40 on 24 October.
On the other side of the coin, the patrol vessel Kittiwake suffered mine damage in the area of the South Goodwin light vessel after straying into part of the Dover Mine Barrage between the Goodwin Sands and the Ruytingen bank.