The General Electric YF120, internally designated as GE37, was a variable cycle afterburning turbofan engine designed by General Electric Aircraft Engines in the late 1980s and early 1990s for the United States Air Force's Advanced Tactical Fighter (ATF) program. It was designed to produce maximum thrust in the class. Prototype engines were installed in the two competing technology demonstrator aircraft, the Lockheed YF-22 and Northrop YF-23. Pratt & Whitney's competing F119 was selected over the F120 to power the ATF, the competition for which the Lockheed team won, and became F-22 Raptor. History Development General Electric (GE) began developing the GE37, which would become basis of the XF120 and YF120, for the Joint Advanced Fighter Engine (JAFE) program in the early 1980s aimed at supplying the powerplant for the Air Force's Advanced Tactical Fighter (ATF). The core technology used in the F120 design was developed during two industry-government programs, the Advanced Technology Engine Gas Generator (ATEGG) and Joint Technology Demonstration Engine (JTDE) programs. The design was meant to address the challenging supercruise requirement of the ATF. This meant the engine had to produce a large amount of dry thrust (without afterburner) and therefore have high off-design efficiency ("design" being standard cruise conditions). Unlike competitor Pratt & Whitney, GE elected against developing a conventional fixed bypass turbofan and instead chose to design a variable cycle engine. Additional innovations include the use of one-piece disk and rotor blade assemblies, or "blisks", in the fan and compressor stages to increase performance and durability as well as reduce weight and parts count. The original RFP called for maximum thrust in the class. Due to the ATF's increasing weight during development from to , thrust requirement was increased by 20% to the class in order to meet performance requirements. GE's design changed to incorporate a 12% larger fan to increase airflow as well as cooling air, particularly for the nozzles. For flight demonstration, YF120s were fitted with the larger fan, unlike the YF119 which used its original small fan. As a result, both demonstrator aircraft had higher performance with the YF120s than with the YF119s. The YF120-powered the YF-22 and YF-23 to supercruise speeds of Mach 1.58 and Mach 1.6+ respectively. While the YF120 engine never went into production, it was installed in the YF-22 for the high angle of attack demonstrations. The Engineering & Manufacturing Development (EMD) configuration of the F120 was tested in