The Pratt & Whitney J75 (company designation: JT4A) was an axial-flow turbojet engine first flown in 1955. A two-spool design in the 17,000 lbf (76 kN) thrust class, the J75 was essentially the bigger brother of the Pratt & Whitney J57 (JT3C). It was known in civilian service as the JT4A, and in a variety of stationary roles as the GG4 and FT4.