The Pentagon may reduce the number of F-35 Lightning II fighters from the fifth batch unless Congress approves $264m in funding.

The additional funding will be used to cover increased development costs in early model jets.

Defense News quoted a document as saying, “If the reprogramming request is not approved, additional funding within the JSF programme will be diverted to cover these costs.”

Two senators from the US Senate Armed Services Committee have opposed cuts to other areas of the defence budget to cover cost overruns in the F-35 Joint Strike Fighter (JSF) programme.

Senator John McCain said, “Based on the current information submitted to the Senate, I intend to oppose the department’s ‘reprogramming request’ to transfer $264m for unacceptable cost overruns on the F-35 programme.”

The JSF is the US’s largest acquisition programme, involving more than $380bn for a total of 2,443 F-35 aircraft.