The use in mining operations of the device known as “taut wire” gear, introduced by Vice-Admiral Sir Henry Oliver, was of great help in ensuring accuracy in laying minefields and consequently in reducing the danger distance surrounding our own minefields.

As our mining operations increased in number we were driven farther and farther out from the German ports for subsequent operations.  This naturally increased the area to be mined as the Heligoland Bight is bell-mouthed in shape, but it had the advantage of making the operations of German minesweepers and mine-bumpers more difficult and hazardous as they had to work farther out, thus giving our light forces better chances of catching them at work and engaging them.  Such actions as that on November 17, 1917, between our light forces and the German light cruisers and minesweepers were the result.  We did not, of course, lay mines in either the Danish or Dutch territorial waters, and these waters consequently afforded an exit for German vessels as our minefields became most distant from German bases.

Broadly speaking, the policy was to lay mines so thoroughly in the Heligoland Bight as to force enemy submarines and other vessels to make their exits along the Danish or Dutch coasts in territorial waters.

At the end of the exit we stationed submarines to signal enemy movements and to attack enemy vessels.  We knew, of course, that the enemy would sweep other channels for his ships, but as soon as we discovered the position of these channels, which was not a very difficult matter, more mines were laid at the end.  In order to give neutrals fair warning, certain areas which included the Heligoland Bight were proclaimed dangerous.  In this respect German and British methods may be contrasted:  We never laid a minefield which could possibly have been dangerous to neutrals without issuing a warning stating that a certain area (which included the minefield) was dangerous.  The Germans never issued such a warning unless the proclamation stating that half the Atlantic Ocean, most of the North Sea, and nine-tenths of the Mediterranean were dangerous could be considered as such.  It was also intended, as mines became available, to lay more deep minefields in positions near our own coast in which enemy submarines were known to work; these minefields would be safe for the passage of surface vessels, but our patrol craft would force the submarines to dive into them.  This system to a certain extent had already been in use during 1915 and 1916.

Schemes were also being devised by Admiral of the Fleet Sir Arthur Wilson, who devoted much of his time to mining devices, by which mines some distance below the surface would be exploded by an enemy submarine even if navigating on the surface.

Such was the policy.  Its execution was difficult.

The first difficulty lay in the fact that we did not possess a thoroughly satisfactory mine.  A percentage only of our mines exploded when hit by a submarine, and they failed sometimes to take up their intended depth when laid, betraying their presence by appearing on the surface.