Boeing 707 ushering in the Jet Age. It established Boeing as one of the largest manufacturers of passenger aircraft, and led to the later series of airliners with "7x7" designations. The later 720, 727, 737, and 757 share elements of the 707's fuselage design. The 707 was developed from the Boeing 367-80, a prototype jet first flown in 1954. A larger fuselage cross-section and other modifications resulted in the initial-production 707-120, powered by Pratt & Whitney JT3C turbojet engines, which first flew on December 20, 1957. Pan American World Airways began regular 707 service on October 26, 1958. Later derivatives included the
Boeing 707 already seen on the −320C. These reduced takeoff and landing speeds and altered the lift distribution of the wing, allowing the ventral fin found on earlier 707s to be deleted. From 1965, -320Bs had the uprated −320C undercarriage allowing the same MTOW. These were often identified as 707-320BA-H. The 707-320C has a convertible passenger–freight configuration, which became the most widely produced variant of the 707. The 707-320C added a strengthened floor and a new cargo door to the −320B model. The wing was fitted with three-section leading-edge flaps which allowed the deletion of the underfin. Three hundred and thirty-five of