Is Britain’s frontier on the Rhine or on the Straits of Dover? Since July, 1940, this question has been a poignant one. It has a more than military significance, however, for it comports great moral issues, the duty or indifference which Britain owes to the Continent of Europe. That it owes only indifference is the theme of one of the most interesting books which the war has produced in English. Sea tower, by T 124, is a book lucid in its composition and extremely compelling in its conclusions. Briefly, the author sets out to show that the original Anglo-French Entente, which first caused us to send great armies to the Continent, arose out of the threat to British sea-power when the Germans began to build a large navy in the first years of this century. This German construction was the result of the appreciation by the Kaiser and his advisers of the doctrine elucidated in Mahan’s classic work on sea-power, that ‘Great Britain, the wealthiest country in the world, possessor of the world’s greatest empire,’ had achieved that position through her naval supremacy. The author maintains that, as the threat was a naval one, it was paradoxical to contribute a great land-army to the struggle on the Continent, and successfully shows that the responsibility rests chiefly upon two men; these were Sir Edward Grey and Sir Henry Wilson, two men whose reputations become more questionable year by year. An expeditionary force, he says, was no more necessary to our interests in 1939 than it was in 1914.