Two Dutch F-35A fighter jets have made their debut at an international air show, conducting demonstration flights in the Netherlands.
Thousands of onlookers gathered at the air force base in the northern city of Leeuwarden, 150km north of the capital Amsterdam, for the first fly-overs.
The radar-evading warplanes, which will eventually replace the Dutch Air Force's fleet of F-16s, are conducting two weeks of testing by Dutch pilots.
The Netherlands, which helped fund development of the new stealthy fighter jet, plans to purchase 37 of the planes in total.
The US Marine Corps has already declared the F-35B model ready for combat, but the conventional take-off and landing A-model is still completing testing.
The US Air Force expects to declare an initial squadron of F-35A jets ready for combat later this year following delayed contract negotiations with Lockheed, the Pentagon's top supplier.
Lockheed has said it hoped to quickly complete the negotiations with the Pentagon for the next two batches of F-35 fighter jets, orders worth about a combined $15bn.
Jack Crisler, a vice president at Lockheed's F-35 program, said that talks were continuing nearly every day, and the two sides were now ‘really close’ to an agreement for the more than 150 aircraft in the net two batches.
Lockheed and Pentagon officials had initially hoped to complete the negotiations by the end of the year, and later moved their target to the end of March, only to miss that mark as well.
Crisler said the discussions were complicated by the scope of the contract, which includes over 150 aircraft, and the subcontractors involved.
"It becomes more and more difficult as you get closer to the end," he said.
Top officials from Lockheed and its main suppliers, Northrop Grumman and BAE Systems, will be in Britain early next month when the F-35 is due to fly at the Royal International Air Tattoo, a large air show outside London, and the Farnborough Airshow a week later.
Crisler said it was possible that the contracts could be completed in time for the air shows.