Unlike many of the concept cars we see at auto shows that are dummied up with clay, smoke and mirrors, Rolls Royce has always pursued an entirely different philosophy, building fully functioning "experimental vehicles."

Each such car has been meticulously hand-built to investigate how a potential production model will operate in real world conditions since 1919, when the first such vehicle (1EX) was constructed, predating the 1938 Buick Y-Job (often claimed to be the world's first concept car) by almost two decades.

The "Torpedo" styled 10EX was built in 1926 as a sports car version of the Phantom 1 and after many modifications, lapped Brooklands at an average speed of 91.2 mph. Most importantly, it stayed in the company as a staff car and occasional celebrity courtesy car for six years, being driven by many people of note, such as Lawrence of Arabia who once borrowed it for a European trip.

Built at a time when Rolls Royce was lavishing each of its creations with extraordinary craftsmanship that it had already created a global reputation for unequaled excellence and reliability (much harder to do in a world where radio broadcasting was still in its infancy), the 10EX Phantom 1 Continental was constructed using a Phantom 1 Continental chassis and engine and a torpedo body produced by the renowned Barker coachwork company in an effort to counter the sporting image of the race-winning Bentleys of the time.

It was commissioned by Rolls-Royce MD, D. Claude Johnson, and the aim was to produce a fast sports car by using a lightweight aerodynamic body. 10EX was built in late 1925. Writing about the development of the 10EX, Henry Royce explained, "The object of preparing this chassis is that, if speed merchants in the form of English peers or Indian Rajahs or others doubt the capacity of the Rolls-Royce Phantom I, this specimen, which we should be able to repeat, can be tried by them… We have no thought of making a freak machine or to depart from the smooth and silent model, but we do think that the owners of the smooth and silent models within their large bodies capable of 80 mph will be pleased to know that the same chassis and engine when fitted to a touring car will be capable of 95-100 mph."

The car was eventually capable of around 95 mph, but only after several sets of extensive modifications, the first of which was a major revamp by Barker in December 1926. After extensive refinement, the car's lap speed at the high speed Brooklands circuit was incrementally pushed from 79.2 mph, to 86.54 mph and eventually to an average lap speed of 91.2 mph – considering that's an average speed, and this was 85 years ago, 10EX was certainly no slouch.

More detail about 10EX and all other Rolls-Royce Experimantal Vehicles can be found in the Rolls-Royce Enthusiasts' Club ( RREC ), 1986 coffe table book entitled " Rolls-Royce And Bentley Experimental Cars " by Ian W. Rimmer, who kindly assisted me with information for this article!

Three more experimental vehicles were produced in order to refine the sports concept (the 15 EX, 16 EX and 17 EX), however,10 EX stayed in the Rolls-Royce family for six years, gathering a provenance unequalled by any EX-designated machine. Rimmer's book mentions, for example, that modifications were held up to 10EX at one stage because Royce was using it as his day-to-day car while his "regular 7EX" was away on official duties

It should also be noted that this car pre-dates the car commonly referred to as the world's first concept car, Harley Earl's Buick Y-Job, by a full 13 years. The 1938 Y-Job was a fully-functioning "experimental vehicle" according to a Buick press release issued at the time, so this vehicle is unquestionably one of the earliest known concept cars in automotive history, preceded by just nine other Rolls-Royce experimental vehicles.

So there you have it. 10EX is unquestionably exquisitely beautiful, it was one of the world's first concept cars, has a splendorous and meticulously documented provenance, and … it's for sale.

RM Auctions has estimated the value of 10EX at GBP400,000-800,000, but it's interesting to note that 17EX sold at an RM Auction in 2009 for GBP429,000 after winning the Trofeo Rolls-Royce as the Most Elegant Rolls-Royce at the 2006 Villa d'Este.

Logically, the 10EX has to be at least the equivalent of 17EX in terms of value - and it was driven by Lawrence of Arabia no less.

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