(6) Aircraft assistance in the shape of three large seaplane stations on the coast of Ireland, with some 36 machines at each station.

(7) The provision of four coal-burning battleships of the “Dreadnought” type to replace Grand Fleet “Dreadnought” battleships which it was desired to use for other purposes.

Admiral Mayo was informed that some 100,000 mines would be required from the Americans for forming and maintaining that portion of the North Sea Barrage which it was suggested should be laid by them, in addition to the large number that it was proposed that we ourselves should lay in the barrage, and that as the barrage would need patrolling by a large number of small craft, great help would be afforded if the United States could provide some of these vessels.  It was estimated at that time that the barrage would absorb the services of some 250 small vessels in order that a sufficient number might be kept constantly on patrol.

It may be of interest to give the history of the North Sea Barrage so far as I can recollect it.  Our views on such a scheme were sought by the United States Navy Department in the spring of 1917.  Owing to various military circumstances, even at that time we had no prospect of obtaining mines in adequate numbers for such work for at least nine to twelve months, nor could we provide the necessary craft to patrol the barrage.  Our view was that such mines as became available during the last months of 1917 would be more effective if laid nearer to the German North Sea naval bases, and in the Straits of Dover, than at such a distance from these bases as the suggestion involved.  Apart from our desire to stop the submarines near their bases, the pros and cons of the scheme were as follows: 

The advantages were: 

(1) That, except for the difficulty of preventing the submarines from using Norwegian territorial waters for egress, a North Sea Barrage would be a menace to submarines using the Kattegat exit as well as those coming from North Sea bases.

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

The disadvantages were: 

(1) The immense number of mines required—­some 120,000, excluding reserves—­and the improbability of producing them in Great Britain.

(2) The great depth of water in which many of them were to be moored, a depth in which no mines had ever been successfully laid before; time would be required to devise arrangements that would enable the mines to be laid at such depths.

(3) The very large number of patrol craft that would be needed to force submarines to dive into that portion of the minefield which was safe for surface vessels and the difficulty of maintaining them at sea in bad North Sea weather.

(4) The difficulty of preventing egress by the submarines in Norwegian territorial waters, in which, even if mines were laid, they would have to be moored at such a depth as not to constitute a danger to vessels on the surface.