Pentagon officials still haven¡¯t set a date for Lockheed Martin Corp.¡¯s F-35, the costliest U.S. weapons system, to complete the final 42% of mission testing to determine whether it¡¯s up to countering the top Russian and Chinese air defenses and fighters.

The F-35 was supposed to fly one month of testing in a highly advanced simulator last December, the latest delay since the original goal of 2017. But that was postponed yet again by unresolved technical problems in the ¡°Joint Simulation Environment¡± test facility, compounded by the COVID-19 pandemic. Then, the Pentagon¡¯s office of operational testing estimated in January that the exercise would commence midyear or by this December.

Defense Department acquisition, legal and testing officials didn¡¯t arrive at a new date when they met last month to review progress of software and verification procedures needed to validate that the simulation of 64 sorties will replicate real-world encounters.

The simulation ¡°will be executed after the JSE capabilities are sufficiently validated, verified, and accredited to conduct the mission trials,¡± Pentagon acquisition spokesperson Jessica Maxwell said in a statement. Asked when the Defense Department¡¯s F-35 program office will set a new schedule, Laura Seal, a spokeswoman, said ¡°we will provide updates when we have them.¡±

The Pentagon¡¯s test office reiterated in a statement its long-standing view that the simulation is necessary as part of legally required testing before Bethesda, Maryland-based Lockheed can proceed with full-rate production. Of a potential fleet of 3,000 or more F-35s for the U.S. and international customers, 720 already have been delivered. Those may need to be retrofitted based on findings from the tests.

Test teams have completed 89 F-35 in-flight missions, according to the testing office, and the 64 remaining sorties in the simulator will complete the missions required in the congressional mandated trials.