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The car was never seen in Bond films, but matches the one that "007" - the code number by which Bond was often known - drove in the movies Goldfinger, and Thunderball.
The vehicle was commissioned by filmmaker Eon Productions and used at promotional events for Thunderball in the United States, the auction house said.
It includes 13 modifications created for Bond, including a Browning .30 calibre machine gun in each fender, tire slashers mounted on its wheel hubs and a bulletproof rear screen that can be raised and lowered.
RM Sotheby's said the Bond modifications had been "properly refurbished to function as originally built," and has had three private owners over 50 years.
The auction will take place on August 15 in Monterey, California.