Book excerpt: In the summer of 1940, a new German aircraft began appearing in the skies over the British Isles. Unlike the rest of the Luftwaffe’s fleet in the Battle of Britain, these aircraft were flying at a height of 40,000 feet and higher – way beyond the reach of the RAF’s defending fighters. These virtually untouchable intruders were examples of the Junkers Ju 86P. The world’s first operational combat aeroplane equipped with a pressurized cabin, they were able to reach a maximum altitude of 42,000 feet. The Ju 86P’s introduction ushered in a new era of aerial warfare, where combat would take place at previously unimaginable heights. The Ju 86P was just one of many high-altitude aircraft projects developed by both the Axis and Allied powers during the Second World War. Others included the Vickers Wellington Mk.VI, Vickers Windsor, Boeing B-29 Superfortress, Junkers Ju 388, Heinkel He 274 and Henschel Hs 130. With pressurized cabins, such aircraft offered obvious tactical advantages: bombers and reconnaissance aircraft could operate safely above the maximum ceiling of the opposing side’s fighters, prompting intense development – especially by the British and Germans – of pressurized interceptors to meet the threat they posed. Combat in the Stratosphere is the first book devoted exclusively to exploring the fascinating story of the development and operational history of aircraft designed specifically for high-altitude operations during the Second World War. But this is not a book solely about the machines themselves. It also focuses on the men who flew these revolutionary aircraft, both in the testing phase and in combat, and the physical challenges these courageous airmen faced, as they pushed themselves to the very edge of physical endurance in this desperate race to reach ever higher altitudes. Drawing on a wide range of sources, including air combat reports, British Cabinet files and Air Ministry documents, as well as first-hand accounts of aeronautical engineers and the pilots who flew these aircraft, Combat in the Stratosphere reveals the full story of this largely overlooked aspect of Second World War air warfare, high above the skies of Europe, North Africa, the Soviet Union and Japan.