A British historian's exhaustive and somewhat plodding examination of submarine warfare during and between two global conflicts. Drawing on a wealth of archival material and secondary sources, Terraine (Trafalgar, The Road to Passchendaele, The Right of the Line, et al.) focuses (perhaps a bit too judiciously) on the formidable role played by Nazi Germany's U-boats during WW II. As the author makes clear, German sub crews performed with deadly effectiveness under the leadership of Admiral Karl Donitz; in fact, the U-boats Korps came perilously close to severing the UK's supply lines. The Allies largely ignored the strategic implications of the submarine's success during the latter half of WW I, Terraine argues; consequently, their shipping proved easy prey for lone raiders and wolfpacks from 1939 through mid-1943. The tide finally turned, he recounts, when the Anglo-American alliance's output of new merchant vessels began to exceed the tonnage sunk. In the meantime, a tough-minded Royal Navy officer named John Walker developed anti-submarine measures that put U-boats on the defensive virtually everywhere they operated. Convoy escorts, radar-equipped aircraft, and improved weaponry exacted a terrible toll on U-boats and the so-called milch cows that permitted flotillas to remain on combat patrols for prolonged periods. All told, 784 German subs were sent to the bottom or captured (against 178 in WW I), and the crews suffered casualties at a rate approximating 85%. Allied forces, however, lost almost 14.7 million tons of shipping and 187 warships to U-boats. By Terraine's account, the victory won by superior manpower and material came none too soon. The Germans were close to deploying a genuine submarine (as opposed to submersible) toward the end of hostilities; if the oceans had not been foreclosed as havens and hunting grounds, moreover, U-boats could have turned D-day into a disaster. Terraine's detailed log is as notable for diligence as drama. General readers with no great interest in annalists' squabbles would be well advised to opt for more vivid narratives, e.g., Dan van der Vat's The Atlantic Campaign (1988) or Edwin P. Hoyt's The Death of the U-Boats (1987).