Book excerpt: The author of The First Day on the Somme details a naval skirmish that became a turning point for the Battle of the Atlantic during World War II. Winston Churchill wrote, “The only thing that ever really frightened me during the war was the U-boat peril.” Had the convoy link between North America and Britain been broken, the course of World War II would have been different. There was a period during the winter of 1942-43 when the Germans almost cut the North Atlantic lifeline. In the first twenty days of March, 1943, the Germans sank ninety-seven Allied merchant ships—twice the rate of replacement. During the same period, seven U-boats were lost and fourteen put in service. No wonder Churchill was worried. Early in March, 1943, Convoys SC122 and HX229 sailed from New York harbor for England, and Admiral Doenitz deployed forty-two U-boats to entrap them. Twenty-one merchant ships were sunk in the ensuing battle. The Germans called it “the greatest convoy battle of all time.” This book documents the convoys, every maneuver of the merchant ships, their escort vessels, the long-range aircraft cover, and the attacking U-boats in a powerful narrative reminiscent of Nicholas Monsarrat’s bestselling novel The Cruel Sea. In many ways, this book could be the story of any of the hundreds of convoys that sailed the ocean during the war. Middlebrook also elucidates three controversial aspects of the Battle of the Atlantic: why there was an “Air Gap” long after full air cover could have been provided, why the convoys had to sail with dangerously weak naval escorts, and how the Allied outwitted the Germans in the radio decoding war.