The first full-scale, unconstrained biography of Sir David Beatty (1871-1936)--""entirely Irish,"" handsome, charismatic, highly ambitious, and, justly, Britain's ""last naval hero"": commander of British battle cruisers at Heligoland Bight, the Dogger Bank, and Jutland (1914-16); commander of the Grand Fleet, after Jellicoe (1916-19); First Sea Lord between 1919 and 1927. Roskill, dean of British naval historians and an expert on naval technology, closely scrutinizes the Royal Navy's notorious deficiencies in fire-control equipment and armor protection, drawing new conclusions from newly-unearthed evidence; he also carefully examines the long-controversial question of Beatty's involvement, as First Sea Lord, in doctoring published accounts of Jutland--finding him culpable, exonerating him partly because he left the relevant documents intact (""to come to light some day""). And, with free use of letters previously suppressed, he lays bare both (American-born, divorced, unstable) Lady Beatty's many infidelities and Beatty's own liaisons, notably--for years--with the wife of a friend. His dash, his hold on his men, and that shady love-affair led, in Beatty's lifetime, to his comparison with Nelson--a comparison which Roskill, citing the latter's far greater influence on events, rejects. His quickness to salt his facts with opinions is, indeed, one of the book's major attractions. And in his portrayal Beatty does come across as a commanding personality, however blemished. Though the amount of technical and strategic detail limits the book to naval buffs, they will find it historically of moment and far more spirited than the norm.