Based on the recently opened Roosevelt-Churchill correspondence as well as more conventional diplomatic sources, this is a rich account of a remarkable collaboration during the pre-Pearl Harbor years of WW II. Unabashedly sympathetic to both men, Lash (Eleanor and Franklin, 1971) underlines their common magnetism, energy, and exasperation with their civil servants; they also shared a preference for extra-official channels, and thus their personal correspondence began when Churchill was still in the admiralty, in September 1939. An ""unspoken naval alliance"" had already been broached by FDR in the spring, Lash records, when the US made secret proposals for naval aid to Britain under cover of a ""neutrality zone."" Somewhat shaken by Churchill's virtual gift of Norway to the Germans, Roosevelt soon exulted at the rise of ""Former Naval Person"" to the prime ministry as the London blitz began, and a destroyer-for-bases deal was worked out which soothed American isolationists. Pursuing his effort to aid Britain, FDR launched an ""undeclared Atlantic war"" in 1942, with the isolationists agreeing to a redefinition of ""defensive waters."" Points of Anglo-American dissension multiplied as the Soviets joined the war and the British pushed for defense of their empire, but Lash says FDR himself agreed with Churchill both on all-out aid to the USSR and on a ""Mediterranean orientation"" for the naval effort. Throughout Lash examines with candor and admiration how FDR manipulated Congress, the bureaucracy, and public opinion, working with Churchill on the phrasing and timing of steps toward American entry into the war. This only enhances the drama, if not the purity, of an intricate collaboration between two undeniable giants.