British motorcycle manufacturers - D

Dalesman	1969-74. Offroad.
Dalton	1920-22
Dane	1919-20
Dart	1901-06 and 1923-24
Davison	1902-08
DAW	1902-05
Day-Leeds	1912-14
Dayton	1913-60. Small engines, clip-ons and scooters after 1954. Made a small machine in 1913, and a scooter in 1955 but closed out in 1960. Dayton: also made an autocycle in 1938.
Defy-All	1921-22
De Luxe	1920-24
Dene	1903-22
Dennell	1903-08
Despatch-Rider	1915-17
Diamond	1910-38. Bought by Sunbeam in 1920.
DKR	1957-66. Scooters.
DMW	Dawson Motors, Wolverhampton. Started by W. 'Smokey' Dawson, who ran a small motorcycle business. Began making rear suspension systems in 1942, then progressed to grass-track 350 and 500cc JAP-powered machines. In 1947 they made a lightweight 125c roadster, moving to a 250cc vertical twin in 1953. Novel frame design used square-section tubing. They also made scooters, the most famous being the 250cc-Villiers powered Deemster. Made mostly trials and racing bikes until the late 1970s.
DOT	'Devoid of Trouble,' founded in 1903 (1902?) by Harry Reed. Name probably originates with his daughter Dorothy's nickname, but the slogan was used in advertising from 1923 on. Started with Peugot and Fafnir engines. Reed won the 1908 TT on one of his Peugot-powered machines, with an average speed of 38.6mph. Reed became a regular competitor after that. DOT switched to JAP engines, then later Bradshaw. In 1926, the company was in financial trouble and had to rebuild, with Reed (50) leaving. The company continued to produce and race until 1932, when the Depression hit. They stayed in business doing contract engineering work until after WW2, when they re-emerged with a strong line in 1949. They lasted until 1973, when the doors closed.
Douglas	Based on Light Motors Ltd., founded by W. J. Barter. He produced his first single-cylinder motorcycle between 1902 and 1904, then turned to a 200cc horizontal twin called the Fee (French for Fairy, which it was later named). The company failed in 1907, but was taken over by the Douglas family, which owned the nearby foundry where Light had purchased components. Douglas concentrated on flat-twin engines in its motorcycles from 1906, using an engine designed by JJ Barter. They turned the engine into a 350cc model for 1907 and sold it through 1910 with increasing success. They won several races and trials events, and became a major supplier of machines in WW1, making 70,000 bikes for the allied effort, including about 25,000 WD models. The 1915 model had a fore-and-aft flat twin engine, belt drive, and full electrical lighting. Douglas built the first disc brakes in the early 1920s. During the 1920s, Douglas had a Royal Warrant for supplying motorcycles to Prince Albert (late King George VI) and Prince Henry. Performance for Douglas machines was good, and their reputation was great, but quality and workmanship were not. Despite this, they won several races including the 1923 sidecar TT and senior TT. Even King George V acquired a Douglas machine in this period. In 1934 they produced a 494cc shaft-drive model called the Endeavour. The company made several products including airplane engines, tractors, Vespa scooters, trucks and cars. In 1935 they were in financial trouble and were taken over by BAC. They continued to make motorcycles, and in WW2 made generators and bikes. In 1948, Douglas was again in economic distress and forced to rationalize its line to a series based on a 350cc flat twin. The last model made was the advanced and novel 350cc Dragonfly, in 1955. Distinctive looks and good handling couldn't hide the low top speed (75 mph, although a sports model claimed 84mph) and poor low-rev performance. A 500cc prototype was shown in 1951, but never made. The company was purchased by Westinghouse Brake & Signal, but new owners were more interested in making Vespa scooters, and motorcycle production ceased in 1957, although they continued to import and assemble Vespas and later Gilera motorcycles.
Downer Groves
Dreadnought	1915-25
Dresda	Developed by racer David Degens, who acquired Dresda Autos in the late 1950s. He started making 'Tritons' (Triumph engines in Norton frames) which became popular race bikes. In 1965 he built a Triton, detuned for greater stability, and won the Barcelona 24-hour race on it. Later he also used Suzuki 500 twin and 750 triple, and Honda 750 quad engines.
Dunelt	Founded by Dunford and Elliott of Sheffield in 1919 with an unusual "supercharged" 499cc two-stroke single at at time when experts felt two strokes would never work above 350cc. Dunelt offered all-chain transmission in 1924. They became involved in sidecars in 1926.  Their bikes broke several records in the 1920s including the first cross-desert ride (Cairo to Siwa and back in 1924) and the Double Twelve Hour World Record at Brooklands on a Model K in 1928. But their 1929 models were not a success and by 1931 the company closed its Birmingham plant. The company continued for a few years, making three-wheelers popular as commercial vehicles, but closed in 1935. A moped with the Dunelt name was shown at the Earls Court show in 1956. Company closed in 57.
Dunkley	1913 and 1957-59 (Different company of same name that made scooters)
DUX	1904-06
Duzmo	1919-23
Dyson-Motorette	1920-22.