The US Air Force is set to declare an initial squadron of the long-delayed Lockheed Martin Corp F-35A fighter jets, which Australia has ordered 72 of, is ready for combat.
US General Hawk Carlisle, who heads Air Combat Command, will announce at a news conference on Tuesday (local time) that the Air Force has an "initial operational capability" of the F-35 jets, said sources, who were not authorised to speak publicly.
Lockheed is building three models of the F-35 Lightning II for the US military and 11 countries that have already ordered the jets: Australia, Britain, Canada, Norway, Italy, Turkey, Denmark, the Netherlands, Israel, South Korea and Japan.
Australia is committed to buying 72 of the aircraft, also known as the joint strike fighter.
The first aircraft are expected to arrive in Australia in 2018 and the first squadron will be in operation by 2021, with all jets up by 2023, the Australian Air Force says on its website.
The Pentagon's F-35 program office said it remained in negotiations with Lockheed about long-delayed contracts for the next two batches of F-35 jets, deals worth about US$15 billion.
"We're seeking a fair deal for the F-35 enterprise and industry," said F-35 program spokesman Joe DellaVedova.
The program, first launched in 2001, has made strides in recent years after huge cost overruns and technical problems that sent the project cost up by nearly 70 percent.
Earlier problems with the fighter jet included issues with the radar software and complications which increased the risk of neck injury to lightweight pilots during the catapult of the seat.
The issues have since been fixed.
Industry and US defence officials say they are working hard to continue driving down the cost of the new warplanes to around US$85 million per plane by 2019, as well as the cost of operating the jets.
"The program is not doing everything they wanted it to do ... But they're at a point now where it is stabilising and so it is progress," said Todd Harrison, a defence analyst at the Centre for Strategic and International Studies.
Officials say the F-35 will give the US military the ability to detect enemy aircraft and other threats far beyond current ranges, allowing the jets to strike targets and disappear long before they are detected.
The US Air Force plans to buy a total of 1763 F-35A conventional takeoff and landing jets in coming years and will operate the largest F-35 fleet in the world.