The global fleet of Lockheed Martin F-35 Lightning II aircraft has accumulated over 50,000 flight hours from 12 different locations.

The program's flight hours are divided into two categories, which include Operational flying hours and System Development and Demonstration flight test hours. Operational flying hours make up the bulk of the count, accumulating approximately 37,950 hours with SDD aircraft flying 12,050.

F-35 Joint Program executive officer Lt. Gen. Christopher Bogdan notes the pace of flight hour accumulation has quickened since the first jet took flight in June 2008.

"The F-35 program continues to grow and accelerate as we complete additional flight testing and increase deliveries to our U.S. and partner warfighters," Bogdan said in a statement. "The next 50,000 hours will be achieved much quicker as we double the size of the F-35 fleet worldwide in the next three years alone."

The 25,000th flight-hour milestone was reached in December 2014, 6 1/2 years after the first flight, with the second 25,000 flight-hour mark reached 14 months later.

The F-35s, which are being developed to replace aging fleets of F-16s, F/A-18s, and A-10s among other aircraft, are being stationed at air bases in California, Florida, Utah, Arizona, South Carolina, Maryland and Nevada.

The multirole fighters are being marketed as fifth-generation aircraft, and have reached the flight milestone as U.S. defense officials remain divided on the future of the program. The U.S. Department of Defense warned the fighter may be being rushed into service in early February, citing a memo detailing a list of problems including safety concerns and software and hardware integration issues.

The U.S. Air Force announced it plans to defer 45 F-35 aircraft from its budget to allow funding for other projects over the next decade on Wednesday.