More evidence has emerged suggesting that Apple may be testing driverless cars in the US.

The company has made inquiries into a former navy base that was converted into a testing grounds for autonomous vehicles.

Apple, which owes its spot on the stock exchange to its incredibly successful computers, phones and tablets, has not publicly announced any plans to release a car.

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But correspondence intercepted by The Guardian in the UK is said to prove that Apple’s Project Titan is far further along in development than any conventional car-maker had feared, and is scouting for secure locations in the San Francisco Bay area to test it.

Brazil’s President Dilma Rousseff takes a ride in a self-driving car at Google headquarters in California. Photo: Getty

The letters printed by the newspaper are between Project Titan Apple engineer Frank Fearon and officials from a nearby car testing facility GoMentum Station.

“We would … like to get an understanding of timing and availability for the space, and how we would need to coordinate around other parties who would be using [it],” said Fearon in May in a letter to the secure test facility.

The GoMentum Station is an ideal test base for Apple since it’s located just 30 minutes’ drive north east from San Francisco and is protected by armed guards.

Until now, much of what Apple has been up to has been based on rumours and hearsay and the fact that it had been reported that the secret car program was being headed up by Apple’s vice-president for product design Steve Zadesky – a former Ford engineer – and Johann Jungwirth, the former head of the research and development department at Mercedes-Benz North America, plus Marc Newson, an industrial designer involved with the 1999 Ford 021C concept car.

Apple itself has never officially confirmed the existence of any plans to build a car, but now the letters from Fearon prove there is substance to the rumours.

It’s not known if Apple plans to team up with another car-maker (there were rumours BMW would donate the i3 architecture) or go ahead, like Tesla, and develop its vehicle from scratch.

Earlier this year Apple’s vice-president, Jeff Williams, described the car as the “ultimate mobile device”.

– with Rose Donohoe