The U.S. Navy assigned $240.7 million to Pratt & Whitney to provide “engineering to mature the F135 engine,” the propulsion system for all three variants of the F-35 Joint Strike Fighter aircraft. The award is a modification to a contract originally issued in 2024, which initiated the design and testing for the F135 Engine Core Upgrade.

That initial contract had a maximum value of $1.3 billion, which has been raised according to succeeding modifications.

The F135 ECU is the Pratt & Whitney-led modernization of the propulsion system, to restore engine life and durability while increasing thrust and thermal management of the engines. The overall goal is provide additional power and cooling needed for the F-35’s Block 4 and future capabilities, including more advanced weapons and sensors.

The F-35 Block 4 update will expand the aircraft’s weapons, sensors, electronic warfare, data-processing, and networking capabilities. It has been delayed and scaled down from the Pentagon’s initial plans, but now is expected to begin in 2031.

The Pentagon opted for the ECU rather than adopt a new F-35 propulsion system to retrofit more than 1,300 fighter jets already in service with the U.S. Air Force, Marine Corps, and Navy, and more than a dozen allied nations.

The current contract modification extends funding for “non-recurring engineering” that will advance the ECU design, and to address operational issues, improve readiness, and support the transition from risk-reduction design review into engineering and manufacturing development (EMD).

The work will be conducted by Pratt & Whitney in East Hartford, Middletown, and Windsor Locks, Conn.; Indianapolis; and West Palm Beach, Fla., and is expected to be completed in March 2028.