The long-range 707-320 Intercontinental became the most commonly ordered version of the 707 airliner. Fitted with turbofan engines, the B designation was added, and very long 6,000 mile routes became possible. After 1962, an 11-fout wide carge door and stronger undercarraige were installed on 707-320Cs, convertible versions of the 707 which could be adjusted to carry both cargo and passengers. Cs became the most popular version of the 707.