The Pratt & Whitney F135 is an afterburning turbofan developed for the Lockheed Martin F-35 Lightning II, a single-engine strike fighter.

The F135 originated with Lockheed Corporation Skunk Works, with efforts to develop a stealthy STOVL strike fighter for the U.S. Marine Corps under a 1986 DARPA project under the auspices of the Advanced STOVL (ASTOVL) program, an early progenitor of the Joint Strike Fighter (JSF) that resulted in the F-35.

The larger turbine was used to provide the additional power required to operate the lift fan through the low-pressure spool shaft, which would be engaged by a clutch in STOVL mode.

[8] ASTOVL continued under the Common Affordable Lightweight Fighter (CALF) program in 1993 before eventually being merged into the Joint Advanced Strike Technology (JAST), which was renamed JSF in 1995; under the JSF program, contracts for flightworthy concept demonstrator aircraft were awarded in 1996 to Lockheed Martin and Boeing for the air vehicle designs and P&W for the initial propulsion system.

A flightworthy prototype system that incorporated the shaft-driven lift fan, designated "YF119-PW-611", was tested on the Lockheed Martin X-35 concept demonstrator aircraft and first flew in 2000.

[12] The first production propulsion system for operational service was scheduled for delivery in 2007 with the purpose of serving the U.S., UK, and other international customers.

[21] Air Force Lt. Gen. Christopher C. Bogdan, the executive officer of the F-35 program, has called out P&W for falling short on manufacturing quality of the engines and slow deliveries.

The company assessed that the uncertainty did not pose a risk to safety of flight but suspended engine deliveries as a result.

Tracy Miner, an attorney with Boston-based Demeo LLP representing A&P Alloys said, "it is blatantly unfair to destroy A&P’s business without allowing A&P access to the materials in question"[25][26][27] In July 2014 there was an uncontained failure of a fan rotor while the aircraft was preparing for take-off.

[29][30][31] As a short term fix, each aircraft is flown on a specific flight profile to allow the rotor seal to wear a mating groove in the stator to prevent excessive rubbing.

[32] Pratt & Whitney managed to meet their 2015 production goals, but "recurring manufacturing quality issues" in turbine blades and electronic control systems required engines to be pulled from the fleet.

[33] Derived from the F119 engine, the F135 is a mixed-flow afterburning turbofan utilizing a similar core as the F119 with a new fan and LP turbine.

[40] At the same time an auxiliary inlet is opened on top of the aircraft to provide additional air to the engine with low distortion during the hover.

[41] The power to drive the fan—about 30,000 shp (22,000 kW)[41]—is obtained from the LP turbine by increasing the hot nozzle area.

[44] Like the F119, the F135 has a stealthy augmentor where traditional spray bars and flameholders are replaced by thick curved vanes coated with ceramic radar-absorbent materials (RAM).

Afterburner fuel injectors are integrated into these vanes, which block line-of-sight of the turbines, contributing to aft-sector stealth.

The axisymmetric nozzle consists of fifteen partially overlapping flaps that create a sawtooth pattern at the trailing edge.

According to Pratt & Whitney, this data may help drastically reduce troubleshooting and replacement time, as much as 94% over legacy engines.

The plans include better cooling technology for turbine blades; this would increase the longevity of the engine and substantially reduce maintenance costs.

[50] In June 2018, United Technologies, parent company of P&W, announced Growth Option 2.0 to help provide increased power and thermal management system (PTMS) capacity, providing options for operators for instance if they are wishing to upgrade to heavier weapons.