This chassis was the fourth of the Experimental Phantom III’s code-named Spectres prepared for experimental use by the Sales Department of Rolls-Royce. The car was on test at the Derby factory on 28 August 1935, and was first used on the road on 3 September. It was registered on 30 September, as RC 3168. On that day it was driven by RR Test driver Lewis to Paris, where it was used as a demonstrator at the Paris motor show. During 1936 the car was used by the Sales Department, including being loaned to HRH Prince George, the Duke of Kent for a weekend in February. Later in that month it was loaned to Sir John Leigh for a day (he ended up buying four Phantom IIIs). In early 1937 the car was returned to the Experimental Department, and for 18 months it was used for testing, including at Chateauroux in France. In October 1937 the car was handed to the Sales Department for preparation for sale. Engine no. 6 was removed and replaced by Unit No. 10 from chassis 31EX.
The chassis was upgraded to latest specifications and renumbered 3AEX33. On 28 June 1938 3AEX33 was sold via George Heath Ltd of Birmingham to James Cadman of Walton Hall, Eccleshall, Lancashire. In 1953 3AEX33 was owned by John L Mackinlay in Yorkshire, and later by Sir Leonard Ropner. By 1960 the Experimental Phantom III was in the USA, owned by George Gray Farr.