It would have been a labour of love to tell at greater length and in more detail how the menace was gradually overcome by the gallantry, endurance and strenuous work of those serving afloat in ships flying the White or the Red Ensigns, but I had not the necessary materials at my disposal for such an exhaustive record.
The volume is consequently largely concerned with the successive steps taken at the Admiralty to deal with a situation which was always serious, and which at times assumed a very grave aspect.

The ultimate result of all Naval warfare must naturally rest with those who are serving afloat, but it is only just to the Naval officers and others who did such fine work at the Admiralty in preparing for the sea effort, that their share in the Navy's final triumph should be known.

The writing of this book appeared also to be the only way in which I could show my keen appreciation of the loyalty and devotion to duty of the Naval Staff, of the many clever, ingenious and audacious schemes developed and carried through for the destruction of submarines and the safeguarding of ocean-borne trade, and of the skilful organization which brought into being, and managed with such success, that great network of convoys by which the sea communications of the Allies were kept open.
The volume shows how the officers who accompanied me to the Admiralty from the Grand Fleet at the end of 1916, in association with those already serving in Whitehall and others who joined in 1917, with the necessary and valuable assistance of our comrades of the Mercantile Marine, gradually produced the measures by which the Sea Service conquered the gravest danger which has ever faced the Empire.
There were at times inevitable set-backs as the enemy gained experience of our methods, and new ones had then to be devised, and we were always most seriously handicapped by the strain imposed upon the Fleet by our numerous military and other commitments overseas, and by the difficulty of obtaining supplies of material, owing to the pre-occupation of our industries in meeting the needs of our Armies in equipment and munitions; but, generally speaking, it may be said that in April, 1917, the losses reached their maximum, and that from the following month and onwards the battle was being slowly but gradually won.

By the end of the year it was becoming apparent that success was assured.
The volume describes the changes carried out in the Admiralty Staff organization; the position of affairs in regard to submarine warfare in the early part of 1917; and the numerous anti-submarine measures which were devised and brought into operation during the year.

The introduction and working of the convoy system is also dealt with.