Command of the air over Germany was seized only when American squadrons arrived to augment the Royal Air Force, upend the existing British doctrine of restricting attacks to nighttime and demand pinpoint bombing of specifically identified German military and industrial targets. The zenith of Allied accomplishment in the air, of course, was D-Day 1944, when a previously unimaginable 11,590 planes were sent aloft. “There had been nothing like it in world history,” Kennedy writes, “nor has there been since. . . . There was no chance for the completely diminished Luftwaffe to do anything except lose more and more of its planes and pilots whenever they rose into the air.” Kennedy goes on to describe how the Allies stopped the ferocious blitzkrieg assaults of 1939 to 1942 by deploying “stronger, tougher and better-equipped forces (with panzers, bazookas, mines, better tactical aircraft)” in concert with the western thrust of the Soviet Army, aided by their T-34-85, which Kennedy calls the “most all-round battle tank” of the war.

Victory in Europe before the summer of 1945 also required the Allies to make hasty progress in perfecting the art of amphibious warfare. After World War I, Kennedy notes, with “a badly defeated and much-­reduced Germany, in a badly damaged and scarcely victorious France and Italy, and in an infant Soviet Union, there were many thoughts of war, but none of them involved the projection of force across the oceans.” The disheartening debacle of the one-day Allied trial effort in August 1942 to breach the Atlantic Wall with a raid against the modest German garrison at Dieppe, France, provided crucial lessons that led directly to the world-­important success on D-Day two years later.

Kennedy shows how wise the Allies were to restrain themselves from invading France until their commanders and troops had gained more experience in amphibious landings and until control of the Atlantic had been secured. He insists that D-Day could have been a rout but for the fact that by mid-1944, British, American and Canadian warriors — from the top down — had transformed their organization into a smoothly functioning apparatus, refined their means of gathering intelligence and designed the now-­famous “bodyguard of lies” that misled the Nazis about when and how the Allies would invade Europe. Succinctly covering the Pacific theater, Kennedy illuminates some of the main tools that enabled United States forces to make their slow progress across the ocean in order to bomb Japan — new fast carrier groups, new fighters like the F6F and bombers like the B-29, as well as the American submarine service and the 325,000 enlisted members of the Navy’s construction battalions, the “Seabees,” which by the end of the war had erected $10 billion worth of military infrastructure around the world.

While Kennedy rightly elevates the importance of technology and those much-too-­unheralded bands of Allied innovators, on a grander scale he fully appreciates that “the winning of great wars always requires superior organization,” which “will allow outsiders to feed fresh ideas into the pursuit of victory.” An ingredient badly missing from the centralized systems of imperial Japan and Nazi Germany was the willingness, demonstrated again and again by top Anglo-American military and political leaders, to share power with those of more modest rank who had greater expertise in tackling a particular problem and who were closer to the action. Kennedy notes that even the dictatorial Stalin “began to relax his iron grasp once he understood that he had a team of first-class generals working for him.”