In the early 1960s, the JT3 was modified into a low-bypass turbofan-the JT3D.
The Pratt & Whitney JT3 revolutionized air transportation when it entered service on the Boeing 707 in 1958. The new turbojet engine was a commercial version of the U.S. Air Force's J53, introduced in 1950. In the early 1960s, the JT3 was modified into a low-bypass turbofan-the JT3D. The first three compressor stages were replaced with two fan stages, which extended beyond the compressor casing to act like propellers. The resulting increase in airflow lowered fuel consumption, noise, and emissions. JT3Ds became widely used, especially on long-range Boeing 707-300s and Douglas DC-8s.