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.

Energetic measures were adopted to overcome this latter defect, but it
took time and but few mines were available for laying in the early
months of 1917.

The result of our minelaying efforts is shown in the following table:

Mines laid Deep mines laid
Year. in the Heligoland off our own coasts
Bight. to catch submarines.

1915 4,498 983
1916 1,679 2,573
First quarter of 1917 4,865 )
Second quarter of 1917 6,386 ) 3,843
Third quarter of 1917 3,510 )

In the Straits of Dover, Thames Estuary and off the Belgian coast we
laid 2,664 mines in 1914, 6,337 in 1915, 9,685 in 1916, and 4,669 in the
first three quarters of 1917.

These last mines were laid as fast as the alterations, made with a view
to increasing their efficiency, could be carried out.

During the early part of the year 1917 the new pattern of mine, known as
the "H" Type, evolved in 1916, had been tried, and although not
perfectly satisfactory at the first trials, the success was sufficient
to warrant the placing of orders for 100,000 mines and in making
arrangements for the quickest possible manufacture. This was done by the
Director of Torpedoes and Mines, Rear-Admiral the Hon. Edward
Fitzherbert, under the direction of the then Fourth Sea Lord,
Rear-Admiral Lionel Halsey.

Deliveries commenced in the summer of 1917, but by the end of September
only a little over 1,500 were ready for laying. Some 500 of these were
laid in September in the Heligoland Bight and were immediately
successful against enemy submarines. More were laid in the Bight during
October, November and December, and the remainder, as they were
pro