Two things made Boeing think about making a jet airliner.
The first reason was because of the Boeing B-47 Stratojet.
The second reason was because of the world's first jet airliner, the de Havilland Comet.

In 1950 Boeing made some details on a jet airliner which they called the Model 473-60C. Airlines were not sure about jet planes because they successful with propeller planes like the Douglas DC-4, DC-6, Boeing Stratocruiser and Lockheed Constellation.

Boeing had sold a lot of planes to the military but they were not very successful with airlines.
Douglas was the most successful airliner maker at the time.
Boeing thought that the only way to get airlines to buy a jet plane was to show them one.

Boeing wanted its jets to have different model numbers from its propeller planes.
The names of the propeller planes all started with 300.
The numbers 400, 500 and 600 were used by missiles and other things, so Boeing made the model number of the jets 700.
The first jet would be the 707.

The Dash 80 was 132 inches (3.35 m) wide.
Boeing wanted to make the 707's fuselage 144 inches (3.66 m) wide.
By the time the 707 was made, its fuselage was 148 inches (3.76 m) in diameter.
The decision to change it did not make many delays, because the Dash 80 was mostly made by hand.
Two things made Boeing think about making a jet airliner. The first reason was because of the Boeing B-47 Stratojet. The second reason was because of the world's first jet airliner, the de Havilland Comet.
In 1950 Boeing made some details on a jet airliner which they called the Model 473-60C. Airlines were not sure about jet planes because they successful with propeller planes like the Douglas DC-4, DC-6, Boeing Stratocruiser and Lockheed Constellation.
Boeing had sold a lot of planes to the military but they were not very successful with airlines. Douglas was the most successful airliner maker at the time. Boeing thought that the only way to get airlines to buy a jet plane was to show them one.
Boeing wanted its jets to have different model numbers from its propeller planes. The names of the propeller planes all started with 300. The numbers 400, 500 and 600 were used by missiles and other things, so Boeing made the model number of the jets 700. The first jet would be the 707.
The Dash 80 was 132 inches (3.35 m) wide. Boeing wanted to make the 707's fuselage 144 inches (3.66 m) wide. By the time the 707 was made, its fuselage was 148 inches (3.76 m) in diameter. The decision to change it did not make many delays, because the Dash 80 was mostly made by hand.
Boeing 367-80