The U.S. Government Accountability Office (GAO) said on May 12 that the Lockheed Martin F-35 Block 4 program must be extended two years due to development delays, adding $1.5 billion to the overall price tag. 

The original schedule called for completing the Block 4 modernization program in 2024, but the timeline must be extended to 2026, GAO said in the watchdog agency’s annual review of the F-35 program. 

The F-35 Joint Program Office initially estimated the cost to develop all 66 new capabilities in Block 4 would be $10.6 billion. The two-year extension to deliver Block 4 raises the development cost to $12.1 billion, with another $3.4 billion budgeted to procure and insert the capabilities in future U.S. F-35s, GAO said.

The Block 4 delays started in 2019. Lockheed planned to deliver the first eight Block 4 capabilities last year, but only one—the automatic ground collision avoidance system—entered service, GAO said. In another example, Lockheed delivered software last year to enable the interim full-motion video capability for the Marine Corps F-35Bs, but failed to deliver the associated hardware, the report said. 

As Block 4 capabilities have entered testing, the Defense Department’s operational testers have noticed other problems. Some of the new capabilities have “caused issues” with existing F-35 functions that previously worked, GAO said. 

“The contractor had not performed adequate testing of the software before delivering it to the test fleet,” GAO said. For its part, the contractor acknowledged the issues and said they would conduct additional testing in software laboratories before releasing future software blocks, GAO added.