The 28th July 1935, in Seattle, State of Washington, a large four-engine aircraft, built by Boeing in response to a request from the United States Army Air Forces effectuated little more than one year before, began its test flights. The aircraft had been obtained by reelaborating two previous projects: one of a four-engine transport aircraft and another one of a bomber aircraft discontinued at the experimental stage, denominated XB 15. The results of the trials were regarded as satisfactory, despite a disastrous accident which destroyed the prototype in October, and a pre-series of thirteen B-17 (denomination given to the new aircraft) was ordered. In 1938 the order for 36 series aircraft finally arrived. From that moment the life of this exceptional flying machine, which would be one of the first to bring a total war on the skies from Europe to the Pacific, officially began. During the conflict 12371 exemplars of the B-17 were produced, which operated at the same time in the two largest war theaters, under either American badges or those of the Royal Air Force, to which some more than 600 exemplars were delivered. But the war debut in the European skies was not an exciting one. When the first massive raids in German territory began, the American, trusting the powerful armament and the heavy armor of their "Flying Fortresses" (as the B-17 were called) used them in bombing missions without aerial escort. It was a very serious mistake for which the crews paid a hard price. The fighter aircraft of the Luftwaffe inflicted such high losses to the "Flying Fortresses" that the American command was forced to revise their theories and better protect their aircraft. It should be recalled that the 27th August 1943, in a single raid over the bearing factories of Regensburg and Schweinfurt, the American lost 60 B-17 out of 376 (and 540 crewmen along with them), and the 14th October, over that same target, 198 B-17 out of 291 (60 downed and 138 damaged to such an extent that they could not be repaired). The crewmen lost in this second mission were more than twice than in the first one. Conversely, the Luftwaffe lost about 50 aircraft in the two actions, despite the Allied propaganda boasting of having downed 186 aircraft in the second raid alone. But let us see the structure of a B-17 of the G series, one of those produced in largest quantities. It was a large four-engine aircraft of low wing and entirely metallic structure, with a fuselage of circular section and a tall vertical tail of characteristic shape. Its structure was particularly lightweight due to the wide utilization of special alloys, but at the same time it offered a foolproof robustness which allowed to whitstand notable damages without compromising the stability of the aircraft. The aircraft was fitted with an electric system which fed almost all of the services, an oleodynamic system used for regulating the cooling of the engines and for the brakes of the landing gear, and an effective centralized system for the entire crew breathing oxygen at high altitudes. There was also a heating system. The notable operational range and the possibility of transporting a good load of bombs rendered the B-17 a terrible weapon. The crew, protected by a thick armor, had thirteen 12.7-millimeter machine guns at their disposal. After the first losses some YB 40, which were B-17 modified by increasing the armor and the armament, were produced. They should have operated as an escort for normal bombers, but this formula was a failure. Fitted with the excellent Norden sight for precision bombing, the "Flying Fortresses" often saw the effect of this device nullified by the infamous tactic known as "carpet bombing". After the war, the B-17 were used in the aviation of many small countries, whereas in their homeland they would be used as "water bombers" for fighting forest fires.