Editing D. Napier & Son (section)

===Interwar period===
[[File:Napier Type 75 TT 1920.jpg|thumb|1920 Type 75 TT]]
By the end of the war, military production had tailed off and the Lion was still barely in use.

In 1919 civilian car production was recommenced. The T75 motor car would be Napier's last. Designed by [[Arthur Rowledge|A. J. Rowledge]] (who left for [[Rolls-Royce Limited|Rolls-Royce]] in 1921), its engine was a 40–50&nbsp;hp {{convert|377|cuin|cc|0|abbr=on}} ({{convert|101.6|x|127|mm|in|abbr=on|disp=or}}) [[alloy]] six with detachable [[cylinder head]], [[overhead camshaft#Single overhead camshaft|single overhead camshaft]], seven-[[Bearing (mechanical)|bearing]] [[crankshaft]], dual [[ignition magneto|magneto]] and [[ignition coil|coil]] ignition, dual plugs, and Napier-[[SU Carburettor]]. Coachwork was by [[Cunard (coachbuilder)|Cunard]], by then a subsidiary.<ref name="Hull, Napier, 1485" /> 187 were built in all by 1924, and Napier quit car production with a total of 4,258 built.<ref name="Hull, Napier, 1485" /> The car was very expensive, costing about the same as a [[Rolls-Royce Silver Ghost]] and in the early 1920s sales were slow. The last car was sold in 1924.

The Lion was by now becoming a best-seller for the company, which eventually dropped all the other aero-engines. The Lion went on to be adapted for land and water, to set the [[land speed record]] in [[Malcolm Campbell]]'s [[Napier-Campbell Blue Bird]] of 1927 and [[Campbell-Napier-Railton Blue Bird]] of 1931 and [[Henry Segrave]]'s ''[[Golden Arrow (car)|Golden Arrow]]'' of 1931 and later in [[John Cobb (racing driver)|John Cobb]]'s [[Napier-Railton]] and [[Railton Mobil Special]], which held the record from 1939 to 1964.

In the 1930s the introduction of much larger and more powerful aero-engines from other companies ended sales of the Lion. Napier quickly started work on newer designs, building on experience gained on the [[X engine|X style]] 16-cylinder, {{convert|1,000|hp|kW|abbr=off}} [[Napier Cub|Cub]], used in the [[Blackburn Cubaroo]] single-engined bomber of the 1920s, and the resulting later 16-cylinder [[Napier Rapier|Rapier]] and 24-cylinder [[Napier Dagger|Dagger]] were both air-cooled H-block designs. Neither the Rapier nor the Dagger proved very reliable, due to poor cooling of the rearmost cylinders, and even the Dagger's {{convert|1000|hp|abbr=on}} was less than its competitors' offerings when shipped.{{Citation needed|date=July 2011}}

As Lion sales faded, an attempt was also made to buy the bankrupt [[Bentley Motors Limited|Bentley]] company in 1931 but Napier was outbid at the last minute by Rolls-Royce. The last vehicle project was a three-wheeled tractor-trailer goods vehicle, but rather than produce this itself, the design was sold to [[Scammell]], which made several thousand.