st submarines, they were also found to be somewhat
unreliable when laid in minefields designed to catch surface vessels,
owing to a defect in the mooring apparatus. This defect was remedied,
but valuable time was lost whilst the necessary alterations were being
carried out, and although we possessed in April, 1917, a stock of some
20,000 mines, only 1,500 of them were then fit for laying. The position,
therefore, was that our mines were not a satisfactory anti-submarine
weapon.

A _new pattern mine_, which had been designed on the model of the German
mine during Sir Henry Jackson's term of office as First Sea Lord in
1916, was experimented with at the commencement of 1917, and as soon as
drawings could be prepared orders for upwards of 100,000 were placed in
anticipation of its success. There were some initial difficulties before
all the details were satisfactory, and, in spite of the greatest
pressure on manufacturers, it was not until November, 1917, that mines
of this pattern were being delivered in large numbers. The earliest
minefields laid in the Heligoland Bight in September and October, 1917,
with mines of the new pattern met with immediate success against enemy
submarines, as did the minefields composed of the same type of mine, the
laying of which commenced in November, 1917, in the Straits of Dover.

When it became possible to adopt the system of bringing merchant ships
in convoys through the submarine zone under the escort of a screen of
destroyers, this system became in itself, to a certain extent, an
offensive operation, since it necessarily forced the enemy submarines
desirous of obtaining results into positions in which they themselves
were open to violent attack by depth charges dropped by destroyers.

During the greater part of the year 1917, however, it was only possible
to supply destroyers with a small number of _depth charges_, which was
their principal anti-submarine weapon; as it became feasible to increase
largely the supply of these charges to destroyers, so the violence of
the attack on the submarines increased, and their losses became heavier.

The position then, as it existed in the early days of the year 1917, is
described in the foregoing remarks.

The _result_ measured in loss of shipping (British, Allied, and neutral)
from submarine and mine attack in the first half of the year was as
follows in gross tonnage:

January - 324,016
February - 500,573
March - 555,991
April - 8