THE RAF’S new F-35 fighter jet can only fly at supersonic speeds for short bursts or it may start to ‘crack’, according to a leaked Pentagon report.

It's been claimed the £100million Lightning II stealth jets are at risk of structural damage when hitting their top speeds of around 1,200mph.

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the problem may make it impossible for the F-35 to conduct supersonic intercepts when in combat adding there was a "risk of structural damage."

Last November it was announced Britain will double its fleet of F-35 stealth fighter jets by ordering 17 more from the States.

The reported deficiencies were first observed in late 2011 following tests where the F-35B and F-35C both flew at speeds of Mach 1.3 and Mach 1.4, it's claimed.

During one post-flight inspection in November 2011, it was discovered one jet had sustained “bubbling (and) blistering” of its stealth coating, according to the documents obtained by Defense News.

Vice Admiral Mat Winter, who leads the F-35 programme for the Pentagon, said his department has taken steps to tackle the problem .

And an MOD spokesperson told the Sun Online: “Our jets have always met the strict safety requirements set by both US and UK military safety authorities.

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“Safety is very closely managed within the F35 programme and we are working with the Joint Programme Office to ensure any issues are addressed as they arise.”

Despite the reports, Donald Trump said today that Poland was interested in buying more than 30 F-35 jets from the US.

Earlier it was reported how the hi-tech coating which makes the fighter jets “invisible” to enemy radar scratches off quicker than expected – and must be replaced after every fight.

An RAF source told the Sunday Express: “This situation obviously has to be rectified before the plane enters operational service”.

They said Mr Williamson and RAF chief Air Chief Marshal Sir Stephen Hillier had always been aware of the problem.

Jeff Babione, vice president of plane makers Lockheed Martin, said: “We inadvertently scratch the coating system, and we have to repaint it”.

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Britain has committed to buying 138 from US defence giant Lockheed Martin and the first batch arrived in June.

In October the MoD was forced to ground its new fighter jet fleet after a faulty fuel tube caused a crash in the US.

Around 250 aircraft were grounded in the US and about 100 worldwide after a US F-35B stealth jet went down over Beaufort, South Carolina, in September.

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