A hell-and-high-water saga that adds luster to the feats of Nazi Germany's storied U-boats during the six months after America's entry into WW II, whilst heaping further obloquy on the US Navy's wholly inadequate response. Drawing on interviews with surviving members of sub crews, ships' logs, and recently declassified archives, Gannon (History/Univ. of Florida) offers a tellingly detailed account of what it was like to wage war from an unterseeboot, plus a wealth of big-picture perspectives. Within days of the Japanese assault on Pearl Harbor, Admiral Karl Doenitz ordered his submariners to prey on shipping that plied sea planes off America's East Coast with the injunction to ""beat the waters like a drum."" Despite ample warning and advice from the experienced British, Admiral Ernest King and his inept subordinates stubbornly refused to accept the necessity of convoying; nor had they the wit to insist on blackouts. In consequence, the U-boat campaign took a terrible toll on unescorted craft, many of which were silhouetted against shoreline lights. By mid-1942, German subs had sunk nearly 400 allied merchant vessels in the eastern Atlantic, Caribbean, and Gulf of Mexico. Gannon's narrative focuses on one of the Fatherland's deadliest marauders, the U-123; commanded by Reinhard Hardegen, it sent 18 ships to the bottom on just two cruises. Among other bold deeds, the ex-skipper recalls passing a night on the bottom of New York Harbor, listening to chamber music broadcast by a local radio station. In recounting Hardegen's exploits, Gannon brings to light little-known facts, e.g., that U-boats traveled and fought mainly on the surface, diving only to avoid danger or very rough seas. Contemporary propaganda notwithstanding, the author notes, there's no evidence German subs fired on lifeboats during Operation Drumbeat; on two occasions, in fact, U-123 came to the aid of crews whose vessels had been sunk. Military history of a very high caliber.