Sir Frederick Banting, co-discoverer of insulin, made this significant remark: "Whichever power gets up to 40,000 feet first and can stay there longest with the heaviest guns will win the war."
Flight at high altitudes poses problems above and beyond those of simple flight. Even in WWI pilots were operating at altitudes where there was not enough oxygen to sustain performance either of the plane or the pilot and competition kept pushing operating altitudes progressively higher. At the beginning of the War in Europe, the B-17 was one of the highest-altitude planes, with an operational altitude of something over 35,000 feet. By 1942 a number of planes were capable of 45,000 feet. Even now, three generations later, the gremlins who live in the stratosphere manage to sneak in and kill the unwary pilot.
Internal-combustion Otto- or Diesel-cycle engines supply power based on the mass of fuel and air in the combustion chamber. As planes go up in altitude the air gets thinner, so less power can be developed by the engine. The solution to this dilemma was the supercharger and especially with radial engines, the turbosupercharger which is an air pump that maintains satisfactory operating conditions in the cylinder. The same kind of air pump was used to pressurize cabins.
Since nearly all of the operational aircraft during WWII were prop-driven, the propeller was a key component of the airplane and was thus of keen interest to the design engineer.
Primary producers of propellers for US combat aircraft were Hamilton Standard Propeller Co, division of United Aircraft Corporation; Curtiss Electric Propeller division of Curtiss-Wright Corporation; and Aeroproducts division of General Motors Corporation. Rotol and deHavilland were important providers in Britain, while Junkers and Escher-Wyss were important suppliers to Germany.
Surprisingly, there are no articles in my collection dealing with the Wright R-1820 9-cylinder radial that powered the B-17 throughout its career.