In about as topical a book as a sea-writer could produce today, a United States Navy officer tells how the Atlantic has been defended in two world wars, and how it may have to be defended against the Russians in a third. The book states its case simply. The Atlantic has been, and is still, our major lifeline to our allies abroad. We must be prepared to keep its sea lanes open and clear of enemy submarines at all costs. His argument is an effective one. He recounts how Germans of two wars---men like Otto Hersing or Hans Rose in World War I; Joachim Mohr or Guenther Prien in World War II----captained submarines which achieved fantastic victories against Allied convoys. But history is not enough. He also discusses at some length how the Soviet Union built its own submarine force (much of it from captured German equipment or technicians), what that force consists of now, and what steps the U.S. Navy is taking to be ready to combat it. The book ends with an interesting description of the possibilities of the atomic submarine in Atlantic underwater combat. A must for the reader interested in current defense problems!