This has been the longest strike at the Fort Worth plant in recent decades, but a 1946 work stoppage last lasted over 12 weeks.

Lockheed has been under pressure from the Pentagon to curb such costs, a contributor to overruns in the nearly $400 billion F-35 program for the planned purchase of 2,443 aircraft. It is the Pentagon’s costliest arms purchase yet.

Three versions of the radar-evading F-35 are being built for the U.S. Air Force, Navy and Marine Corps. Eight countries helped fund the development and are in varying stages of buying it - Britain, Norway, Canada, Denmark, the Netherlands, Turkey, Australia and Italy. Japan and Israel have placed multibillion-dollar orders for the aircraft.

The F-35 is also competing with Boeing’s F-15 Silent Eagle and Eurofighter for a 60-plane order from South Korea, a contract that will likely be awarded before the end of the year.

Lockheed is continuing to use temporary workers to maintain production schedules for the F-35 and the multirole F-16, updated versions of which are still being built for export.