Apart from the STOVL version's problems, the biggest issue was integrating and testing the software that runs the aircraft's electronics and sensors.

ECONOMIST: The defence industry

The main cause of the delays and cost over-runs, he says, is a problem with the weight of the STOVL version that came to light in 2004.

ECONOMIST: The defence industry

It suggested cancelling the STOVL version of the F-35 and cutting the rest of its order by half, while buying cheaper F-16s and F-18s to keep numbers up.

ECONOMIST: The defence industry

The Marine Corps variant (F-35B), a short take-off and vertical landing variant (STOVL), was grounded for nearly a month after a manufacturing defect caused a fuel line to detach just before a training flight in January.

BBC: Grounded US F-35 fighter jet fleet to resume flights