The Armstrong Siddeley ASX was an early axial flow jet engine built by Armstrong Siddeley that first ran in April 1943. Only a single prototype was constructed, and it was never put into production. A turboprop version as the ASP was somewhat more successful, and as the Armstrong Siddeley Python saw use in the Westland Wyvern. History In December 1941, Metrovick ran its Metrovick F.2 engine for the first time. While successful, the engine was too heavy to be a useful aircraft engine, and the Royal Aircraft Establishment (RAE) felt this was probably due to Metrovick's history as a steam turbine manufacturer without much aircraft experience. The RAE approached Armstrong Siddeley with an offer to help with the design, both to improve the F.2 and to get the company familiar with turbojet design so they might build their own designs, or others under license. However, Metrovick refused the offer, and no amount of effort on the part of Armstrong Siddeley or the RAE would change their opinion. Now highly interested in jet propulsion, Armstrong Siddeley began looking for other designs they could work on, and eventually hired Fritz Albert Max Hepner. Hepner had a design similar to the early designs of A. A. Griffith, in that the engine did not use separate compressor and turbine stages, but combined the two by attaching an individual turbine stage to each compressor stage, and rotating each stage in opposite directions. The main difference between Hepner's design and Griffith's was that the stages were not connected to a central shaft, but instead to a surrounding rotating shell. The RAE was not impressed with this design, and repeatedly refused to provide funding for its development, suggesting instead a much simpler design. Another major critic of the concept was Armstrong Siddeley's chief engineer, Stewart Tresilian, who had grudgingly taken the post in 1939 at the request of the RAE. The Armstrong Siddeley board fired Tresilian in January 1942 and submitting their latest design proposal; once again it was rejected. It was not until August 1942 that the company was finally convinced to begin work on a simpler design. Like the F.2, the plan was to use the RAE's compressor designs while Armstrong Siddeley would develop the turbines and the rest of the engine. This new experimental design became the ASX. An order for six examples was placed in October 1942, and the contract signed on 7