"Introduction World War II was one of the most profound events in the history of mankind. It now seems like ancient history@ and yet in the relatively brief time span of 1939 to 1945 technology in all aspects of warfare advanced in leaps and bounds??none more so than in piston engine development. Virtually the entire world was embroiled in a struggle of good against evil. Aviation played a major part in this monumental endeavor; indeed many major battles were fought solely in the air. Who can forget the inspiring words spoken by Winston Churchill: ""Never in the field of human conflict was so much owed by so many to so few."" The ""few@"" of course@ were the brave Royal Air Force (RAF) pilots@ flying Supermarine Spitfires and Hawker Hurricanes@ who@ outnumbered@ fought against Messerschmitt Bf 109s and Bf 110s as well as hordes of bombers@ predominantly Heinkel He 111s and Junkers Ju87s. Victory in the Battle of Britain saved Britain from invasion by Germany@ although it was an incredibly close-run thing. Halfway across the world two years later in 1942@ another pivotal battle took place in the Pacific??the Battle of Midway??which again was fought entirely by aircraft@ although this time all the aircraft that took part were based on aircraft carriers instead of on land. Interestingly@ the ships involved never saw the opposing side@ such was the scale of the battle. Historians are still arguing about who was really the victor in the Battle of Midway. In terms of losses it was probably a stalemate; however@ the fact that the Japanese had been stopped in their tracks represented a major psychological victory for the United States. Air battles often involved huge formations of overloaded bombers struggling and fighting their way to the target. As the war progressed@ it was not unusual for the U.S. Eighth Air Force and British Royal Air Force (RAF) to attack a target with 1000 bombers@ giving rise to the phrase ""aluminum overcast"" to describe an event surely never to be repeated. Even transport aircraft hauling muchneeded equipment to battle fronts were subjected to constant harassment and attack by the opposing side. The resupply effort undertaken by the Fourteenth Air Force flew some of the most dangerous missions of World War II@ flying over such incredibly inhospitable territory as the Himalayas in overloaded Curtiss C-46 Commandos and Douglas C-47 Dakotas in poor weather@ constantly exposed to attack by Japanese fighters. Such was the pace of the war that it was imperative to get the finest equipment with best performance into service as quickly as possible. This led to some of the shortest development times ever achieved for complex military hardware. On occasion this abbreviated development and testing cost dearly@ as in the case of the Boeing B-29@ which suffered numerous problems during its introduction to combat service@ as did the Avro Manchester with its failure-prone Rolls-Royce Vulture engines. Germany compromised its long-range bombing capability because of the insurmountable problems with the Daimler Benz DB 610 and DB 613 engines installed in the Heinkel He 177. Japan forced many underdeveloped aircraft@ particularly those with poor engines@ into combat during the later stages of the war when they realized that the Zero@ as fine an airplane as it was@ just was not competitive after 1942. The struggle for air superiority by all sides focused on squeezing the most performance out of the available technology as well as Herculean efforts to advance technology. Although there were many instances of aircraft with inferior performance coming out victorious@ the odds were obviously stacked against this occurrence. Throughout the conflict a seesaw battle of technology was waged. Part of this technological battle was in the area of engine development@ as this is the most influential aspect of the performance of an aircraft@ although it could be argued that an aircraft featuring old-technology aerodynamics but with a superior power plant will not outperform an aircraft with state-of-the-art aerodynamics and a mediocre engine. For example@ the P-40F powered by the single-stage Rolls-Royce Merlin was still a mediocre performer. Conversely@ the P-51A@ powered by the Allison V-1710@ was still a good performer; however@ when the P-51 was redesigned to take the two-stage Rolls-Royce Merlin@ the aircraft came alive and was arguably the finest fighter aircraft built in World War II. This book attempts to document the remarkable development that took place with these mechanical masterpieces produced during the conflict and that often shaped the tactics and strategy of the battles."