Bentleys of this era are known as Derby Bentleys because they were built in the Rolls-Royce factory located in Derby, England. Those of Bentley's previous independent era are Cricklewood Bentleys.
Chassis series A to F were 3½ Litre cars; G to L (excluding I) were 4¼ Litres, and the M series was the 4¼ Litre Overdrive chassis. Each series consisted of 100 chassis numbers, either odd or even. The numbers 13 and 113 in each series were not used, to avoid upsetting superstitious customers.
Beginning in March, 1936, a 4¼ Litre version of the car was offered as replacement for the 3½ Litre, in order to offset the increasing weight of coachwork and maintain the car's sporting image in the face of stiff competition. The engine was bored to 3½ in (88.9 mm) for a total of 4.3 L (4257 cc/259 in³). From 1938 the MR and MX series cars featured Marles steering and an overdrive gearbox. The model was replaced in 1939 by the MkV, but some cars were still finished and delivered during 1940–1941.
1234 4¼ Litre cars were built, with Park Ward remaining the most popular coachbuilder. Many cars were bodied in steel rather than the previous, more expensive, aluminium over ash frame construction.
A Drophead 4¼ Litre was featured as James Bond's car in the 1983 movie "Never Say Never Again".