“They do,” Masiello said.

Radar mountings in the F-35’s nose are different for the APG-81 and the APG-85 radar–a difference which has helped complicate fielding of the new radar which was to deliver with F-35 Lot 17.

The Air Force has been considering an APG-81/APG-85 dual-mount bulkhead, though the latter may take two years to field.

The service’s fiscal 2027 future years defense plan (FYDP) contains $133 million in fiscal 2031 for retrofitting 14 F-35As with APG-85s–a unit cost of $9.5 million per radar, and outside the FYDP the service said it plans to spend about $1.6 billion to retrofit another 167 jets with the APG-85.

The Air Force, Navy, and Marine Corps have 832 F-35s out of a global inventory of more than 1,300 on 42 bases and 13 ships–10 U.S. ones and three allied ones, according to the F-35 program.

The APG-85 is critical to the 55 upgrades in the Block 4 program–22 of which have fielded so far, including seven last year, and six on target for this year, Masiello testified on June 23. For full functionality, the APG-85 and Block 4 require 62 kilowatts to 80 kilowatts (kW) of cooling, however, versus the 32 kW on the plane now.

The current mission capable rate of the F-35 is 56 percent, and the full mission capable rate is 25 percent.

In October, 2018, then Defense Secretary Jim Mattis told the Air Force and Navy to boost the mission capable rates of their key fighters to 80 percent within a year.

“My job is clear: deliver a reliable and affordable system capable of sustaining high operational tempo, with a path to achieving 80 percent mission capable rates no later than 2030,” Masiello said in his prepared testimony on June 23.

Sustainment is another significant challenge for the F-35 program, as it seeks to boost the inventory of spare parts and support more fighters.

“Our current sustainment system was built to support a fleet of 700-800 aircraft,” Masiello said in his prepared remarks on June 23. “To date, the government has accepted over 1,300 F-35 aircraft worldwide. To address this scaling challenge, we reset our sustainment strategy, increased government oversight, and optimized all aspects of sustainment planning and execution. We are right-sizing spare parts based on validated performance modeling, updating our maintenance processes to enable effective maintenance at all levels, and modernizing our logistics digital systems to enable audit, enhance government control, and connect F-35 with the broader Joint Force.”

The Pentagon FYDP includes more than $13 billion for the F-35’s Global Support Solution (GSS) Reset.

A version of this story originally appeared in sister publication Defense Daily.