The U.S. Air Force on Tuesday declared an initial squadron of Lockheed Martin Corp. F-35A fighter jets ready for combat, marking a major milestone for a program that has faced cost overruns and delays.

The move is another achievement for the $379 billion program, the Pentagon's largest weapons project. The Air Force follows the U.S. Marine Corps, which declared a first squadron of F-35s ready for combat in July 2015.

"The U.S. Air Force decision to make the 15 F-35As at Hill Air Force Base combat ready sends a simple and powerful message to America's friends and foes alike — the F-35 can do its mission," F-35 program chief, Air Force Lt. Gen. Chris Bogdan, said in a statement.