It was, of course, the obvious counter to the submarine campaign, and it appealed with force to that considerable section which feels vaguely, and rightly, that _offensive_ action is needed, without being quite so clear as to the means by which it is to be carried out.
In this particular case I informed the clever and able officers to whom the planning of the operation was entrusted that they were to proceed on the assumption that we intended to seal the enemy's ports somehow, and that they were to devise the best possible scheme, drawing up all the necessary orders for the operations.

This was done in the most complete detail and with great care and ingenuity, but at the end there was no difference of opinion whatever as to the inadvisability of proceeding with the operations.
It is to be observed in connexion with this question that sealing the North Sea bases would not have been a complete cure, since submarines could still make their exit via the Kattegat, where we could not block channels without violating the neutrality of other nations.
The final conclusion arrived at _was to use a combination of the last three alternatives_ provided that _a satisfactory type of mine_ could be produced in sufficient numbers and a sufficient supply of small craft provided by ourselves and the United States.
Full details were given to Admiral Mayo of the proposed North Sea Barrage on a line totalling 230 miles in length, which was divided into three parts, Areas A, B and C, of which Area A only would be dangerous to surface vessels.
It was estimated that Area A would require 36,300 mines, and it was proposed that this area should be mined by the United States forces with United States mines.
It was proposed that the British should mine Area B, the requirements being 67,500 mines, and that the United States should mine Area C, for which 18,000 United States mines would be required.
The reasons governing the selection of the mine barrage area were fully given, and the advantages arising from the use of the United States pattern of mine instead of the British mine for Areas A and C were stated.
Admiral Mayo was also informed of our intention to establish a mine barrage in the Channel, on the Folkestone-Grisnez line, as soon as mines were available, with a strong force of patrol vessels stationed there, whose duty it would be to compel enemy submarines to dive into the minefield.

He was further made acquainted with our intended policy of still closer minelaying in the Heligoland Bight.
Although Admiral Mayo was not actually informed of the details of the future policy which it was hoped to adopt in the Adriatic for the improvement of the Otranto Barrage, various schemes were at the time being worked out between the British, French and Italian Admiralties, having as their object the prevention or obstruction of the exit of enemy submarines from the Adriatic, in the same way as it was hoped to obstruct German submarines from making their exit from the North Sea without incurring heavy losses.

The great depth of water in the southern part of the Adriatic constituted the main difficulty facing us in the solution of this problem.

In August, 1917, it was, however, definitely decided to establish a barrage of nets and mines across the Straits of Otranto, and the work was put in hand.