Aug. 5 (UPI) -- The cost of the U.S. military's F-35 Lightning II Joint Strike Fighter plane program is increasing, the Defense Department said last week in an acquisition report.
The report, an update to its 2020 budget and delivered on Friday, noted that the cost of the F-35 program grew by $25 billion in 2018, and is the "main driver" of a four percent increase in overall military spending.
The increase is, in part, because of upgrades to the planes and programs, known as Block 4, which modify existing planes with new systems and weapons as new threats are recognized. The modifications are also added to planes in production.
Overall costs include the Block 4 modifications, designing F-35s to carry nuclear weapons, increased use of onboard software, and higher expenses of deploying the planes.
The costs are estimated over the expected 53-year expected lifespan of the planes, and include design and development, repairs, modifications and upgrades, as well as spares and operations.
The announcement of cost increases came days after Sen. Chuck Grassley, R-Iowa, called for greater transparency and accountability in the management of the F-35 program. In a letter to Defense Secretary Mark Esper on July 25, Grassley urged resolution of ongoing issues in the F-35 program, notably its cost.
"When we met last week, I was impressed with your commitment to rein in wasteful spending and get the Pentagon's financial problems in order," the letter read in part.
Grassley later notes the need of "rooting out waste at the Department of Defense, citing the necessity for budgetary discipline, a culture of cost awareness, accountability of Department employees, and the importance of earning the trust and confidence of the Congress and the American people."
The U.S. plans to have over 2,000 F-35s -- the Air Force, Navy and Marines each fly a variant of the aircraft -- replacing much of the military's aging fighter fleet, with hundreds more of the aircraft sold to allied militaries around the world.