The F135 Enhanced Engine Package (EEP): variant-common, combat-tested, coalition-assured and cost-effective. For full Block 4 capability and $40B savings over the lifecycle of the program to keep our military on the leading edge.


EEP is the most cost-effective, lowest-risk propulsion modernization solution for the F-35 weapons system.

As the air vehicle grows, so must the engine. Designed with the knowledge that operational environments evolve and threats advance, the F135’s modular design and advanced digital architecture allow for spiral development and insertion of both hardware and software – ensuring the F-35 outpaces emerging threats.

Pratt & Whitney developed EEP for the F135 with the objective of providing an affordable, low risk, and agile pathway to fielding meaningful propulsion capability for all F-35 customers. EEP leverages Department of Defense investments in adaptive technology to deliver the capability needed for Block 4 aircraft, while maintaining the variant-commonality and international partnership approach that the joint program was built upon. Doing so maximizes affordability for all, with EEP generating approximately $40B in lifecycle cost savings over the life of the program.

Additionally, low technical risk is a must for pilot safety on a single-engine fighter. Based on operational experience, today’s F135 is the safest fighter engine ever produced. As a derivative design, EEP builds upon the same proven architecture that has more than one million flight hours of safe and dependable operation so pilots can complete their mission and return home safely.

A modernized F135 engine meets the timeline and necessary requirements to support Block 4 aircraft without disrupting the program of record or driving increased cost and risk. 

  • Variant-Common

    EEP is the only modernization solution that maintains variant commonality, a foundational element of the F-35 program’s design to drive economies of scale and reduce cost. As such, EEP leverages the existing production and sustainment infrastructure, and maintains the current cost share ratios with the Services and Partners. Additionally, EEP is production cost neutral, retaining the sizable affordability investments that have been made to date.

    All told, EEP saves the taxpayer approximately $40 billion in lifecycle costs over the life of the program, making it the most cost-effective modernization available for the F-35 enterprise. Those are substantial savings that can be put to use for other modernization priorities across the Department of Defense.

  • Combat Tested

    EEP enhances an engine that is combat-tested and serving the warfighter now, powering missions for more than a dozen customers around the world. As a derivative design, EEP builds upon a proven architecture that has more than one million flight hours of dependable operation between the F135 and the F119, which powers the F-22 Raptor.

    Weight neutral and requiring minimal airframe integration testing, EEP was designed from the onset to be integrated into production and/or retrofit during engine overhaul – enabling the accelerated fielding of fully supported Block 4 capabilities in the capacity needed by the warfighter.

  • Coalition-Assured

    EEP’s variant commonality strengthens the combat capability and capacity of key allies who serve as a vital pillar in U.S. national security and defense strategies at a time when geopolitical instability across the globe is increasing.

    EEP enables critical Block 4 capability for all F-35 operators, while maintaining the international partnership and alliance approach of the program -- preserving the ability to share cost and logistics over a broad enterprise to ensure F-35 interoperability and sustainability across multiple variants and users.

  • Advanced Capability

    EEP leverages the Department of Defense’s investment in adaptive technology to deliver the required capability growth – all within the confines of the existing program construct. This means EEP incorporates the latest in propulsion technology – including advanced aerodynamics and durability component technologies – to meet or exceed the necessary requirements for Block 4, while retaining variant-commonality to maximize affordability.

    Performance improvements include:

    • Greater than 10% more range
    • Greater than 10% more thrust
    • Greater than 50% more thermal management capacity
    • 5% gain in powered lift for the F-35B variant


More about the F135