Porsche’s longest-surviving car is set to go under the hammer…

Porsche's longest-surviving car, a 1939 Type 64, is set to head to auction later this month.

One of just three ever built — and what is thought to be the only example left in existence — the Type 64 was developed and produced by company founder Ferdinand Porsche for a 940-mile road race that would start in Berlin and end in Rome in spring 1939.

Though the car was completed, the outbreak of the Second World War resulted in the cancellation of the competition.

Based on the Volkswagen Beetle, the Type 64 utilised an air-cooled, rear-mounted 985cc engine rebuilt with dual Solex carburettors, larger valves and a higher compression to produce between 32 and 39bhp — up from the base unit's 23bhp output.

Two further examples were proposed to be built despite the Second World War for testing and experimentation purposes. The second car was completed though, in the waning stages of the war, was commandeered by members of the U.S. Seventh Army's 'Rainbow' division — who are said to have then cut the roof off and then drove it around, before the engine ceased. It is believed to have been left for scrap.

The body of the third example was completed in 1940, though had not been mounted onto a chassis and was used for crash repairs on the original 1939 example instead.

Following the Second World War, Ferdinand Porsche had been imprisoned by French authorities. During this time, his son — Ferry Porsche — assumed control of the company and would use the Type 64 has his own personal car, continuing to use it until 1947 when it was sold to Austrian racer Otto Mathé in 1947.

Following this sale, the now-iconic 'PORSCHE' badging was fitted to the front of the Type 64 – becoming the first car to sport it — with Mathé retaining ownership until his death in 1995. It changed hands to fellow Austrian Thomas Gruber, before being sold again in 2008 to an anonymous German-based car collector who currently owns the vehicle.

Said to be the 'ancestor of all Porsches', this 1939 Type 64 will be offered by RM Sotheby's at its Monterey Auction, taking place in California, USA from August 15 to 17. The auction house has not publicly stated an estimated price for its sale, though CNBC reports it could fetch $20m (circa. £16.4m).