Green, and incorporated the findings of research into aluminium air-cooled cylinders by Samuel D. Heron and Professor A. H.

There they were required by official policy to suspend work on the RAF.8 and focus efforts to get the unreliable Siddeley Puma into effective service, an engine that had been ordered in large numbers despite a lack of testing.

Initial performance was not as expected; as a result the stroke was increased to 5.5 in (139.7 mm) on all variants after the Jaguar I.

[4] The most powerful version of the engine, the Jaguar VIC, produced a maximum of 490 hp (365 kW) on takeoff at 1,950 rpm and weighed 910 lb (413 kg).

[6] A preserved Armstrong Siddeley Jaguar is on public display at the Science Museum (London).