A point which, until recently, unaccountably seemed to have escaped notice was that the work of the Dover Patrol was carried out on behalf of all the {15} Allies and of the United States. It was not a British force acting solely in British interests. Though it is difficult, and perhaps invidious, to apportion the credit for protecting the Allied lines of communication, yet there is no shadow of doubt that the troops from Canada and from the United States of America owed to the Dover Patrol force a tremendous debt of gratitude for their safe passage overseas. Recognition of this fact has since been shown by the erection at New York, and on the French coast, of memorials to the Dover Patrol. When the late war has faded into history, and those of us who took part have long since "gone west," such memorials will remain to bear witness to the splendid sacrifice and unselfish gallantry of those hardy seamen who did their utmost to uphold the honour of civilisation and to destroy the forces working for its overthrow. (This opportunity of acknowledging the success of their extremely arduous efforts, humble and brief though the acknowledgment may be, partially counterbalances my regrets at not having had the chance of serving with the "Dover Patrol" except on the occasion which this book is designed to describe.) [Illustration: CAPTAIN ALFRED F. B. CARPENTER, V.C., R.N.] The final closing of the Straits, however, was far from accomplished by the spring of 1918. At that time we had reason to believe that a large percentage of the total Allied losses in merchant ships was caused by the Flanders submarines, and that the percentage was on the increase.