The Boeing 707 originated from design studies into an improved version of the military Model 367, then in production for the United States Air Force (USAF) as the C-97. Many configurations of aircraft were considered until finally the 80th configuration was chosen and the aircraft was then dubbed the Model 367-80. With no government funds available, $16 million of the companies funds were used to construct a prototype and the project was officially launched on May 20, 1952. At the time of the project go-ahead, Boeing had changed the way in which it allocated model numbers. As a result the new aircraft would be designated in the 700 block as the 707. The prototype Model 367-80/707 (registered N70700) was rolled out at Renton on May 14, 1951. The aircraft made its first flight from Renton on July 15, 1954 and in August 1955 the aircraft received great publicity by doing two complete barrel rolls over Lake Washington with test pilot A M Tex Johnston at the controls. Initially airlines found the cabin of the 707 to be too small. Boeing subsequently increased the width and length of the cabin. The first order for the aircraft was received from Pan American World Airways (Pan Am), with the airline ordering 23 707-121's. The order was later changed for 15 of these aircraft to become 707-321's. The first 707-121 for Pan Am was rolled out on October 28, 1957 and made its first flight on December 20, 1957. Pan Am's fifth 707 aircraft (N711PA) inaugurated the first revenue-earning 707 flight on October 26, 1958. A unique variant of the 707 was produced for Qantas - the 707-138. This aircraft featured a 3m (10ft) fuselage reduction to allow the carriage of additional fuel. Altogether 138 commercial 707-100's were delivered before production ceased. The Boeing 707-200 was another one off variant produced for Braniff International Airways. The aircraft featured larger thrust engines to improve hot-and-high take-off performance. Braniff had an initial order for five aircraft but one was lost a pre-delivery acceptance flight and thus only four entered service.
The next variant of the 707 to appear was the 707-300 Intercontinental. The aircraft was designed for transoceanic routes. The 707-300 featured a lengthened fuselage which enabled the aircraft to carry around 189 passengers. The wing span and wing area was also increased along with the horizontal tail span. Pan Am was also the launch customer for this version of the 707 and the first delivery to the airline took place on July 19, 1959. The improved 707-300B featured changes including an extension to the wingspan and curved wingtips. Pan Am was once again the launch customer and ordered 31 707-321B's on February 13, 1961 with the first entering service on June 1, 1962. The 707-300C was also launched by Boeing, which was a convertible cargo/passenger aircraft. It featured a large cargo door on the port side of the forward fuselage. Pan Am was launch customer and ordered 15 707-321C's on April 25,1962. The 707-300 was the most popular variant of the 707 aircraft family. A total of 545 commercial model 707-300's were built, the final example being delivered to Nigeria Airways on January 30, 1978. The 707-400 was similar to the 707-300 but featured Rolls-Royce Conway 50B turbofans. Launch customer for this variant was BOAC with the first delivery taking place on February 12, 1960. A total of 37 707-400's were built with other customers being Air India, Cunard Eagle, El Al, Lufthansa and Varig.
The Boeing 720 was a derivative of the 707 designed for operating short to medium range routes from shorter runways. The aircraft was originally referred to as the 707-020 and then the 717-020 before the designation 720-020 was finally agreed on. The aircraft was 2.7m (9ft) shorter than the 707-100. Other changes included a redesigned wing with new full-span leading edge Kruger flaps. Maximum capacity was for 165 passengers in an all-tourist class layout. United Airlines was the launch customer for the 720 and ordered 29 of the aircraft. The fist example was put into service on July 5, 1960. A total of 154 720's were built with the final example being delivered to Western Airlines on September 20, 1967.