Pratt & Whitney began developing its first production turbofan—the JT3D—during the late 1950s.
It was a low-bypass-ratio engine built around the J57's service-proven core. The JT3 made its first flight on a Boeing 707-120 aircraft on June 22, 1960. Shortly thereafter, McDonnell Douglas selected it for versions of the DC-8.
The military version of the JT3D—the TF33—powered the first flight of the Air Force's B-52H Stratofortress on March 6, 1961. The Air Force also used it for transports such as the Lockheed C-141 Starlifter and Boeing C-135B Stratolifter. In 1973, the Air Force selected a TF33 model for its E3A Airborne Warning and Control System (AWACS) airplane manufactured by Boeing.