Dover Barrage

The Dover Barrage was an underwater blockade by England of German submarines attempting to use the English Channel during World War I.

[1] The first evidence of effectiveness was on 4 March 1915, when the German U-boat U-8 was taken, caught in the indicator nets.

[2] Both sides initially believed the barrier to be effective and the Germans attributed some submarine losses to it.

The British moved the barrier to cover Folkestone-Cap Gris Nez and used new mines and searchlights, effectively closing the Channel to hostile submarines in August 1918.

[1] Underwater scanning of the area covered by the Dover Barrage shows the wreck of SM UB-109 broken in half.