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.

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.

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 motor launches were employed for anti-submarine work, fitted with hydrophones, and worked in company with drifters and torpedo-boat destroyers, or in minesweeping in areas in which their light draught rendered it advantageous and safer to employ them instead of heavier draught vessels to locate minefields, and in the Dover area they were largely used to work smoke screens for operations on the Belgian coast.

Owing to the rise of tide enemy destroyers could pass over the minefields at high water without risk of injury, and they frequently did so pass.

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.

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.

In the case of a convoy encountering a minefield, as in the case of a fleet, several ships may be sunk practically simultaneously.

(2) That the enemy would be unable to sweep up the minefield, owing to its distance (over 200 miles) from his bases.