The engine that became the Jaguar was initially designed at the Royal Aircraft Factory Farnborough (R.A.F) during the First World War under the direction of Major F. M. Green and aero-engine designer S. D. Heron, it was known as the R.A.F.8.  During 1917 there was much political chicanery surrounding the Royal Aircraft Factory and some members of staff moved to other operations; Major Green and Heron Joined Siddeley Deasy taking the R.A.F.8 design with them. Because there were issues surrounding the AS Puma engine development of the R.A.F. 8 into the Jaguar was delayed until 1918.

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