The Armstrong Siddeley Viper was originally developed as an expendable turbojet engine for the GAF Jindivik drone aircraft. It had a short lifespan of about ten hours. Later it was improved with a much longer life span and went on to power many aircraft including the RAAF’s Macchi MB326H trainers.
The Viper was basically a larger version of the earlier Armstrong Siddeley Adder which was a turbojet version of the Armstrong Siddeley Mamba turboprop engine.
The Viper engine was designed in the early 1950s as a cheap, expendable engine to power the Australian Jindivik target drone aircraft. It entered service in this version in 1953.
When a new long-life turbojet engine of about the same weight, size and performance was required it was more cost effective to improve the Viper than the design and develop a totally new engine.
The short-life version of the Viper generated 8.45kN (1,900lb) of thrust and later long-life versions generated up to 12.01kN (2,700lb) thrust.
The Viper engine was produced for fifty years, first by Armstrong Siddeley and they by successor companies Bristol Siddeley and Rolls Royce. More than 5,500 Viper turbojet engines were built.