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.

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.

[2] 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.

[3] 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.

[4] Due to the ATF's increasing weight during development from 50,000 lb (22,700 kg) to 60,000 lb (27,200 kg), thrust requirement was increased by 20% to over 23,500 lbf (105 kN) in military/intermediate power and 35,000 lbf (156 kN) class in full afterburner 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.

The more ambitious F120 design was judged to be riskier, and General Electric also accrued fewer testing hours than Pratt & Whitney.

[11][12] Technology from the YF120 has been applied to subsequent GE designs; in the 1990s, GE, Allison Engine Company, and Rolls-Royce (Allison was acquired by Rolls-Royce in 1995) began jointly developing the F136 engine for the Joint Strike Fighter program, which resulted in Lockheed Martin being selected to develop and produce the F-35 Lightning II.

The high and low-pressure spools are counter-rotating, which eliminates the stationary vanes between the turbines and reducing the number of parts and decreasing weight.

[22] The wedge shapes of the nozzle flaps also reduce the infrared signature by flattening the exhaust plume and mixing it with shed vortices for cooling.