The stunning Bentley Le Mans Speed Six once belonged to the City of Edinburgh Police and was used to chase villains in the Scottish capital in the 1930s.
Welsh First World War hero Lt Col Ernest Helme was the car’s first owner, buying it new from HM Bentley & Partners in London in May 1930.
He clocked up 18,000 miles in little more than a year haring back and forth between Kensington and the Gower Peninsula before part-exchanging it for a new model in 1932.
The next owner was an R Whitson of Glasgow, although Bentley historian Michael Hay has established the Speed Six was later used by the Edinburgh police.
After being founded as the world’s first citywide police force in 1805, the mobile unit was set up in 1926 by long-serving chief constable Roderick Ross.
The unit was hampered at first by the lack of quality and power of its handful of vehicles, a problem that would have been resolved by the purchase of the six-and-a-half litre Bentley.
The Speed Six was then sold to an RG Weddell in 1946 and fitted a new lightweight body by Riverlee Motor Bodies of Birmingham, before fetching up in America in the 1960s.
It then passed into Norwegian ownership and finally returned to the States 21 years ago via the renowned British Bentley dealer, Stanley Mann.
The current owner has spent tens of thousands of dollars on maintenance to keep the car on the road as a long distance tourer.
It will go on sale on Thursday as part of Bonhams’ annual Scottsdale Auction in Arizona with a guide price of £550,000-£740,000.
In its sale catalogue, Bonhams notes: “As recorded in the latest edition of Hay’s Bentley The Vintage Years 1919-1931, the Speed Six is understood to have remained in Scotland for some time and was used by the Edinburgh City Police in the 1930s – one might well pity the thief with two tons of Bentley chasing after them, it must have proved quite a deterrent!”