The squadron of about 12 planes is based at Hill Air Force Base in Utah and the planes' combat rating -- known as initial operational capability -- comes after completion of a raft of tests and training exercises.
"The F-35A will be the most dominant aircraft in our inventory, because it can go where our legacy aircraft cannot and provide the capabilities our commanders need on the modern battlefield," said General Herbert "Hawk" Carlisle, who heads the US Air Combat Command.
"This is just the beginning, this is an interim step that will get us to what the full combat capability of the F-35 eventually will be," Carlisle said.
The US Marine Corps last year announced that an initial group of F-35Bs had attained initial operational capability, though these have not yet been used in combat.
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With a price tag of nearly USD 400 billion for a total of 2,443 F-35 aircraft -- most destined for the Air Force -- the plane, built by Lockheed Martin, is the most expensive in history.
But the program has faced numerous setbacks, including a mysterious engine fire in 2014 that led commanders to ground planes until the problem could be resolved.
Other issues have led to delays and cost overruns, including software bugs, technical glitches and even a faulty eject system that risked killing pilots who weighed less than 136 pounds (62 kilos).
The Air Force's F-35A is one of three variants of the aircraft, designed to conduct conventional landings and take offs.