Top Pentagon civilian and military officials continue to express optimism over reaching the in-service deadlines of mid-2015 for the U.S. Marine CorpsF-35B and mid-2016 for the U.S. Air Force’s F-35A.

Concern, however, still looms over a plan to reach initial operational capability (IOC) for the F-35C, designed for aircraft carrier suitability, in 2018.

Meanwhile, the U.K. plans for initial service for its F-35Bs in 2018. At issue for that goal are projected challenges with "data fusion," or the aircraft’s ability to digitally connect to its wingmen and create integrated sight pictures for pilots that include comprehensive threat data and coherent targeting.

"The software is not the driving factor in achieving IOC in 2015," says Frank Kendall, Pentagon procurement chief. "The story is different for [F-35 software version] 3F … We are about six months behind software development there if we don’t do anything different or anything better."

Early testing revealed "ghost tracks" and duplicate tracks of targets on cockpit screens, says Orlando Charvalho, executive vice president for F-35 prime Lockheed Martin. These have since been removed, he says, through software improvements.

The biggest challenge for achieving the Marines’ IOC by July 1, 2015, is ensuring that 10 F-35s are outfitted with the 2B software — which offers limited weapon and sensor capability — to the same variant standard in time, says Lt. Gen. Christopher Bogdan, F-35 program executive officer. At issue is that these aircraft rolled off Lockheed Martin’s production line at different times and some have modifications installed based on flight-test lessons, while others don’t. But for ease of operation they must be the same configuration.

This work is on the "critical path" to the Marines’ IOC, and Bogdan says he is "fairly confident" it is achievable. The Air Force is planning to declare IOC as early as Aug. 1, 2016, with the 3i software configuration, which includes the 2B functionality hosted on updated computer software; the software is suitable for release to international partners.

Flight testing of the 2B software is slated to wrap up by year’s end, says Lorraine Martin, F-35 executive vice president.

She is confident that the company also will deliver 3F software as planned in 2018. "We have planned 3F with the actual productivity out of 2B," she says, noting the actual data on 2B progress underscores her conviction. "We hit 2B essentially on the nose" once the program was rebaselined in 2010 with more realistic targets, she says.

Lockheed Martin is about 53% through the flight-test program.

The F-35 is slated to cost $398 billion to develop and field for the U.S.; also participating in the program are the U.K., Italy, The Netherlands, Canada, Denmark, Turkey, Australia and Norway. Singapore, Japan and Israel also have plans to buy the single-engine, stealthy jet, as well.