on other manufacturers Douglas's traditional layout of a flat-twin engine mounted with its cylinders parallel to the frame had been copied by several motorcycle manufacturers in the 1910s and 1920s. The Williamson Flat Twin, made in Coventry from 1912 to 1914, was a litre-class heavyweight motorcycle using the Douglas layout and with the engine, forks and gearbox made by Douglas. In the United States, Indian made their lightweight Model O from 1917 to 1919 and Harley-Davidson made their middleweight Model W from 1919 to 1923, both using the Douglas layout. Several German manufacturers began making motorcycles with the Douglas layout when engine manufacturer BMW made their M2B15 flat-twin proprietary engine available in 1920. The M2B15 had been developed from the reverse engineering of a Douglas motorcycle engine. See also List of Douglas motorcycles List of car manufacturers of the United Kingdom References External links Douglas motorcycles at the Open Directory Project London Douglas Motorcycle Club Vintage vehicles Defunct motorcycle manufacturers of the United Kingdom Cyclecars Scooter manufacturers Motorcycles powered by flat engines Defunct companies based in Bristol 1907 establishments in England 1957 disestablishments in England British companies disestablished in 1957 British companies established in 1907