RAF F-35B Lightning ll aircraft, from Edwards Air Force Base in California, USA

The operational testing of the UK's first F-35B Lightning II aircraft, at Edwards Air Force Base in California, ahead of their introduction in 2018 has been well publicised.

What has not however been reported, and only hinted at on internet forums, is that the British aircraft are rumoured to have been fitted with a previously unheard of 'cloaking device'.

One of the aircraft, being flown and maintained exclusively by Royal Air Force and Royal Navy personnel at the United States Air Force base, is understood to have temporarily 'disappeared' last week while undertaking a routine test flight. 

A source has told Forces.tv that American staff including several visiting top brass were left stunned as the Joint Strike Fighter vanished shortly after take-off.

It's understood the pilot prematurely triggered the device while making an adjustment to his £260,000 Generation III helmet display system.

Amid much consternation and alleged heated exchanges several USAF staff were later allowed a brief visit to a hanger on the base for a demonstration of the top secret technology.

A grainy image, snapped in low light on a smuggled-in smart phone and sent anonymously to Forces HQ, appears to show ground crew working on a virtually invisible aircraft. 

Image and video hosting by TinyPic

The accompanying text suggests the technicians are from the MOD's Defence Science and Technology Laboratory (DSTL) at Porton Down. Disguised in US Army and Air Force fatigues they've previously been able to fool their American counterparts and move freely around the California facility without raising suspicion.

Watch: Porton Down - Inside Britain's Top Secret Science Centre 

As far back as the 1980s the idea of a Klingon-style cloaking device has been something of a Holy Grail for stealth aircraft designers at the likes of Boeing's Phantom and Lockheed Martin's Skunk Works.

So much so that during early years of the F-117 Nighthawk stealth fighter program, where the aircraft operated in total secrecy, fake 'cloaking' pods were mounted on A-7 Corsairs operating out of the same remote Tonopah Test Range. 

Image and video hosting by TinyPic

Built from napalm bomb shells the mysterious attached pods drew prying Soviet satellites and inquistive eyes away from the Nighthawks, allowing the Senior Trend project to exist for over a decade before the aircraft's existence was publicly acknowledged.

Now the metaphorical cat's out of the bag on the F-35B upgrade, Forces.tv has been told 'off the record' by our source, codenamed April, that plans are in place to sensationally 'reveal' the Lightning II in-flight at the Royal International Air Tattoo (RIAT) at RAF Fairford this summer.

More: First Ski Jump Take-Off For UK's F-35B Lightning II 

Forces TV is available on Sky 264, Virgin 277 and Freesat 652

(Photo of “cloaking device” pod courtesy of the Stealth Fighter Association)

This article was originally published on April Fools' Day 2016.