For some time we had been using Decoy vessels, and with some success; it was possible to increase the number of these ships at the cost of taking merchant ships off the trade routes or by building.  A very considerable increase was arranged.

The use of our own submarines offensively against enemy submarines had also been tried, and had met with occasional success, but our numbers were very limited (the total in December, 1916, fit for oversea or anti-submarine work was about forty).  They were much needed for reconnaissance and offensive work against surface men-of-war in enemy waters, and only a few were at the time available for anti-submarine operations, and then only at the cost of other important services.

The hydrophone had been in the experimental stage and under trial for a considerable period, but it had not so far developed into an effective instrument for locating submarines, and although trials of the different patterns which had been devised were pushed forward with energy, many months elapsed before it became a practicable proposition.

One of the best offensive measures against the enemy submarines, it was realized, was the mine, if laid in sufficiently large numbers.  Unfortunately, in January, 1917, we did not possess a mine that was satisfactory against submarines.

Our deficiency in this respect was clearly shown in the course of some trials which I ordered, when one of our own submarines was run against a number of our mines, with the result that only about 33 per cent. of the mines (fitted, of course, only with small charges) exploded.  The Germans were well aware that our mines were not very effective against submarines.

We possessed at the time mines of two patterns, and whilst proving unsatisfactory against 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.