The Pratt & Whitney JT4A was an axial-flow turbojet engine of the late 1950s. A two-spool turbojet in the 17,000 lbf (76 kN) thrust class, it was essentially the bigger brother of the Pratt & Whitney JT3C.

Before the arrival of the Pratt & Whitney JT3D turbofan engine, the JT4A was used to power certain Boeing 707s and Douglas DC-8s models. It was used to improve field performance in the medium-range Boeing 707-220 and Douglas DC-8-20, and to achieve intercontinental range in the original Boeing 707-320 and the Douglas DC-8-30. In military use the JT4A engine had the designation J75, which was used in the Lockheed U-2, the Republic F-105 Thunderchief, the Convair F-106 Delta Dart and the Avro Arrow prototype.

Turbojet engines