Lockheed Martin’s F-35 jet developed more cracks during testing last year and wasn’t sufficiently reliable in training flights, according to an annual report from the Pentagon’s chief tester.On-ground tests of the Air Force and Marine Corps versions of the fighter revealed “significant findings” of cracks on five occasions in fuselage bulkheads, flanges, stiffeners and engine mounts “that will require mitigation plans and may include redesigning parts and additional weight,” according to the report on major weapons released this week by Michael Gilmore, director of operational testing.Gilmore has repeatedly raised questions about progress on the Fort Worth-based F-35 program, the most expensive U.S. weapons system, and cited cracks in the short-takeoff version of the fighter jet a year ago. This year’s report may draw particular scrutiny because the Pentagon will propose increasing purchases to 42 planes in fiscal 2015 from the 29 Congress authorized this year.Michael Rein, a Lockheed spokesman, said in an emailed statement that Gilmore’s report also outlined “a tremendous amount of positive information” and said the findings highlighted known problems.“The F-35 aircraft has flown to every corner of the envelope and is meeting or exceeding expectations in flight performance,” Rein said. “The challenges identified are known items and the normal discoveries found in a test program of this size and complexity.”Joe DellaVedova, Pentagon spokesman for the F-35, said in an e-mail that “there were no surprises in the report. All of the issues mentioned are well-known to us, the F-35 international partners and our industry team.”“Although the report is factually accurate, it does not fully highlight the F-35 enterprise’s efforts to address and resolve the known technical and program-related challenges,” he said.The F-35 is being built at Lockheed’s west-side complex where more than 6,000 employees are directly involved in the program. In December, Lockheed completed the 100th F-35, capping a year in which the company and Pentagon reported progress on cost and technical issues.In the new report, Gilmore disclosed an incident in late September when a bulkhead “severed.” He said “analysis and corrective actions” were continuing.Aircraft based in Florida, Arizona, California and Nevada for pilot training missions continue “to be immature” and rely “heavily on contractor support and workarounds unacceptable in combat operations,” Gilmore wrote.Reliability measures “are all below” target goals for the current stage of development, he said.Gilmore also warned of delays in testing and fielding software for the Marine Corps version, the F-35B, which the service has said it hopes to declare operational by December 2015.General James Amos, the Marine Corps commandant, said at a Rand Corp. conference earlier this week that development of what’s known as 2B software “is going better than probably others might have thought.”“It’s actually what I would call at this point probably medium risk” as the aircraft approaches initial combat capability, Amos said. This report includes material from Star-Telegram archives.