Pratt & Whitney J75

The Pratt & Whitney J75, sold to airlines as the JT4A, is a two-spool axial-flow turbojet in the 17,000 pounds-force thrust class that first flew in 1955. It was essentially the bigger brother of the Pratt & Whitney J57. In military service it powered the Convair F-106 Delta Dart, the Lockheed U-2 and the Republic F-105 Thunderchief, and it was also used in prototype and experimental aircraft such as the Avro Canada CF-105 Arrow and the Lockheed A-12. As the JT4A it powered certain Boeing 707 and Douglas DC-8 models until the JT3D turbofan arrived. Its marine and power generation derivative, the FT4, proved far more durable than the aircraft engine itself, with over 1,000 sold.