The first was the knowledge that the Germans themselves had laid minefields in some portions of the Bight, and it was necessary for our minelayers to give such suspected areas a wide berth.

Sir Reginald Bacon had put forward a proposal for a deep minefield on the line FolkestoneCape Grisnez, but confined only to the portion of the line to the southward of the Varne Shoal.

The provision of "flares" for illuminating minefields at night, and a system of submarine detection by the use of electrical apparatus were also matters which were taken up and pressed forward during 1917.

Some disagreement arose on the subject of the provision of the necessary number of vessels for patrolling the minefield with a view to forcing the submarines to dive.

This fact constituted the principal disadvantage in the use of a buoyed channel, but in certain places where the traffic was heavy the procedure was inevitable, and it greatly simplified the work of the patrol craft and minesweepers; the only precautions possible lay in the use of alternative marked channels, and in the laying of defensive deep minefields outside the channel in which enemy submarines might compass their own destruction.

Admiral Bacon suggested later the extension of the minefield to the westward of the Varne Shoal, so as to make it a complete barrier across the Channel.

With this end in view a still further addition to the minelaying fleet became necessary, and since the mining would be carried out at leisure in this case and speed was no great necessity for the minelayer owing to the distance of the minefields from enemy waters, an old battleship was put in hand for conversion.