It was inadvisable to use merchant ships, since every vessel was urgently required for trade or transport purposes, and the alternative was to fit men-of-war for minelaying.  The only old vessels of this type suitable for mining in enemy waters were ships of the “Ariadne” class, and although their machinery was not too reliable, two of these vessels that were seaworthy were converted to minelayers.  In addition a number of the older light cruisers were fitted with portable rails on which mines could be carried when minelaying operations were contemplated, in place of a portion of the armament which could be removed; a flotilla of destroyers, with some further flotilla leaders, were also fitted out as minelayers, and several additional submarines were fitted for this purpose.

For a projected special scheme of minelaying in enemy waters a number of lighters were ordered, and some of the motor launches and coastal motor boats were fitted out and utilized for mining operations on the Belgian coast towards the end of 1917.

By the end of that year 12 light cruisers, 12 destroyers and flotilla leaders and 5 submarines had been fitted for minelaying.  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.