Armstrong-Siddeley Motors was formed in 1919 when Armstrong Whitworth Development Company bought Siddeley-Deasy, which had built aircraft engines during WWI.
In 1935 Armstrong-Siddeley Motors became a subsidiary of Hawker Siddeley, which merged with the engine business of Bristol Aero Engines to become Bristol Siddeley in 1960, and then with Rolls-Royce in 1966.
The Adder was a pure jet version created in 1948 from the Armstrong Siddeley Mamba ASM3 airscrew gas-turbine by removal of the airscrew gearing. This resulting a very slender turbojet with a long air intake spinner housing the generator.
It was used to power two experimental aircraft :
- The Swedish Saab 210
- The Australian GAF Pika