In World War II, when the Allies were planning to launch strategic bombing against the Axis powers, a fatal problem arose, that is, the Allies lacked suitable long-range escort fighters, and the bombers could only rely on themselves to survive the most dangerous mission phases. However, at that time, there was an opinion that bombers could defend themselves with their own firepower or repel incoming enemy fighters, and the problem was that the number of ** configurations was insufficient.
Following this line of thinking, the idea of converting existing bombers into escort bombers emerged, which simply means that the ammunition payload capacity of the aircraft was abolished, and the number of guns on board was increased instead, and the density of fire was increased, so that it could accompany the bomber group and drive out the invading enemy fighters. In September 1942, the United States tried to modify the B-17 for escort missions, the B-17 was the main model of the Allied forces to carry out strategic bombing in Europe at that time, the modified bomber was called the XB-40, and then the experimental service model of the small batch modification was called the YB-40.
As a large bomber, the B-17 itself has a relatively comprehensive configuration, with multiple 12 installed in the nose, back, tail, etc7 mm machine guns (the number of machine guns varies depending on the model), but the German fighters found their weak point, and when attacking from a few degrees directly in front of the bomber, they were only threatened by a small number of machine guns. The YB-40 increased the number of machine guns to 14, which also meant that more personnel were needed, usually 14 16 people, with a maximum of 30 people.
The distribution of machine guns of the YB-40 was sufficient to cover all directions of the aircraft, and 2 units were installed in the nose turret and the tail turret 12 each7 mm machine gun; The B-17 originally had a turret on the back, and the YB-40 added one above the radio room, both of which were mounted with two 127 mm machine gun; The firing points on both sides of the waist of the fuselage are not set with turrets, but with large-sized firing windows, and the machine gunners must wear heavy flight suits, and the left and right windows are appropriately staggered so as not to interfere with each other, and 2 are installed side by side in each window127 mm machine gun; A spherical turret was added to the belly, and there were also 2 machine guns of the same model.
Theoretically, the more machine guns, the more conducive to firepower, YB-40 canceled the magazine, and increased the armor protection for the members of the formation, the magazine can be used to store spare ammunition, generally the aircraft can carry more than 10,000 rounds of ammunition, if the aircraft reduces the fuel load, you can carry more aircraft***YB-40 is not only one ** configuration, has tried a variety of schemes, such as installing 6 machine guns in the turret under the nose, or installing a cannon, etc.
A total of 25 YB-40s were modified, they did not show the desired effect, the aircraft itself was bulky, the rate of climb and flight speed were weakened, the bomber could increase the flight speed after dropping bombs, but the accompanying YB-40 could not keep up; And the on-board firepower was not as reliable as expected, and the clumsy YB-40 could not cope with the nimble fighter and could not provide adequate protection to his teammates.
The YB-40 was only in service until October 1943, but it was not without merit, and some of the experience was applied to other bombers, although this experience quickly became obsolete after World War II.