laying. Two old
cruisers had been added to the minelaying fleet and several other
vessels were in hand for the same purpose. The detailed plans of the
arrangements were prepared and the work of fitting out minelayers
carried out under the supervision of Admiral R.N. Ommanney, C.B., whose
services in this matter were of great value. The rapidity with which
ships were added to the minelaying fleet was largely due to his efforts.

On the entry of the United States of America into the war a further
development of mining policy became feasible. The immense manufacturing
resources of the United States rendered a large production of mines an
easy matter, with the result that as soon as the United States Navy
produced a reliable type of mine the idea of placing a mine barrage
across the northern part of the North Sea which had been previously
discussed became a matter of practical politics. With this end in view a
still further addition to the minelaying fleet became necessary, and
since the mining would be carried out at leisure in this case and speed
was no great necessity for the minelayer owing to the distance of the
minefields from enemy waters, an old battleship was put in hand for
conversion.

With the enormous increase in the number of mines on order the problem
of storage became of importance, including as it did the storage of the
very large number, some 120,000, required for the northern barrage. The
Third Sea Lord, Admiral Lionel Halsey, took this matter in hand with
characteristic energy, and in conjunction with United States naval
officers made all the necessary arrangements.

The United States mines were stored in the vicinity of Invergordon, and
the British mines intended for use in the northern barrage were located
at Grangemouth, near Leith, where Rear-Admiral Clinton Baker was in
charge, as well as in other places, whilst those for use in the
Heligoland Bight and Channel waters were stored at Immingham and other
southern depots.

The laying of the North Sea mine barrage was not accomplished without
very considerable delay, and many difficulties were encountered. It was
originally anticipated that the barrage would be completed in the spring
of 1918, but owing to various defects in both British and United States
mines which made themselves apparent when the operations commenced, due
partly to the great depth of water as well as to other causes, a delay
of several months took place; and, even when near comp