Boeing 707 center section tanks. Its first flight was on January 11, 1958; 69 turbojet 707-320s were delivered through January 1963, the first passengers being carried (by Pan Am) in August 1959. The 707-420 was identical to the −320, but fitted with Rolls-Royce Conway 508 (RCo.12) turbofans (or by-pass turbojets as Rolls-Royce called them) of 18,000 lb (79 kN) thrust each. The first announced customer was Lufthansa. BOAC's controversial order was announced six months later, but the British carrier got the first service-ready aircraft off the production line. The British Air Registration Board refused to give the aircraft a certificate of airworthiness,
Boeing 720 costs, which allowed it to be successful despite few sales. The company built 154 Boeing 720s and 720Bs from 1959 to 1967. The 720's wing modification was later added on the -120B and on -120s retrofitted to the B standard. The Boeing 720 is a four-engined low-wing cantilever monoplane. Although it was similar to the Boeing 707, compared with the 707-120, it was 9 ft (2.73 m) shorter in length, and had a lighter structure through use of lighter forged metal parts and thinner fuselage skins and structures. The rearmost of the 707's over-wing emergency exits was deleted on each