Primarily this is the submarine war- from September '39 to April '49 with a brief summary of the final period after the upward curve of disaster had turned is favor of the Allies. With the Atlantic sea lanes a vital link to victory, cooperation was reached only after deadlocks and overcoming weaknesses in defense and skill. As in his earlier books, Morison succeeds in combining basic factual data with magnificent episodic story telling. Good reading.