The Siddeley Deasy Motor Manufacturing Company Ltd. based in Coventry was a British manufacturer of automobiles, airplanes and engines. The company has existed since 1906. 1919 it was combined with the vehicle and engine division of the Industrial Group Armstrong Whitworth Armstrong Siddeley.

Origin, the company was founded as a Deasy Motor Car Manufacturing Co. of Henry Hugh Peter Deasy in February 1906, which was created through the acquisition of Iden Motor Car. Deasy asked her motor vehicles. After an argument with his chief engineer Deasy left his company in 1909. John Davenport Siddeley was Managing Director and in 1912 took over the control, and where he. Siddeley Deasy in the company Motor Manufacturing Company Ltd renamed.

During the First World War, the company flourished. The car production was stopped. Since 1916, we focused on the manufacture of aircraft, including the Royal Aircraft Factory RE7 and the Royal Aircraft Factory RE8. From 1917 also aircraft engines were developed and manufactured. Main type with 4,288 pieces was the Siddeley Puma.

Already 1917 Siddeley Deasy could establish itself as a supplier for workpieces made of cast light alloy Armstrong Whitworth. There was a steady partnership that eventually in 1919 to the partial merger of the two companies led to Armstrong Siddeley Motors Ltd.. called it.