In this book our concern is with the war at sea, and with a part only of that gigantic effort. But of this part, every word that has been said holds good. The submarine and anti-submarine campaign is not a series of minor operations. Its history is not a mere episode among chapters of greater significance. On the contrary, the fate of Britain, and the fate of Germany, were speedily seen to be staked upon the issue of this particular contest, as they have been staked upon no other part of the world-wide struggle. The entrance of America into the fellowship of nations was involved in it.