Grace's Guide is the leading source of historical information on industry and manufacturing in Britain. This web publication contains 143,446 pages of information and 230,060 images on early companies, their products and the people who designed and built them.
Siddeley-Deasy Motor Car Co of Coventry
1910 November. Details of the 12hp, 14-20hp, 18-24hp and 24-30hp cars.
1911 March. Details of the 18-24hp car.
1911 Introduced the 12-hp 1,946cc chassis known as the 'R Type'.
1911 The Deasy name prevailed at this time because of objections from Wolseley about using the name Siddeley.
1912 The cars used the slogan "As silent as the Sphinx" and started to sport a Sphinx as a bonnet ornament, a symbol which become synonymous with descendant companies.
1912 Formed Stoneleigh Motors to build a light cars.
1912 July. Details of the 18-24hp Special Light car.
1912 October. All models are now sleeve-valve. Details of the 14-20hp, 18-24hp, 24-30hp plus the Stoneleigh.
1913-1917 For a list of the models and prices of Cars see the 1917 Red Book.
1913-1917 For a list of the models and prices of Petrol Motor Commercial Vehicles see the 1917 Red Book under the name Stoneleigh.
1913 April. Advert for the 18-24 hp model. 'Makers of luxurious cars of medium power'.
1913 Stoneleigh Light car. 
1914 Employing around 500 employees and producing 600 cars per annum.
1914 March. Details of the 30-36hp car.
1914 October. Details of the 14-20hp, 18-24hp and the 30-36hp cars.
1915 Won contract to build 300 aero-engines RAF 1A - a 90-hp V8 based on the Renault V8. Only 25 built before it was replaced by a 150-hp V12 model.
Order for 650 aero-engines type RAF 4A
Appointment of A. J. Susten as accountant having joined in 1912
From 1916 built air-frames. 100x RE7 and later 1,000x RE8 types.
WW1 Siddeley-Deasy grew to have 5,000 workers; the company produced trucks, ambulances, and staff cars. In 1915 airframes and aero-engines started to be produced as well. Siddeley-Deasy were one of six companies which produced the Royal Aircraft Factory R.E.8 aircraft from 1916.
1919 January. Advert that states that in the last four years, while they have been producing for the nation, they have made 1,750,000 aircraft engines and their spare parts; very large numbers of RE8 reconnaissance aircraft and over 1,000 motor vehicles. 
Siddeley remained in charge until 1935.