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The Saunders Roe SR.53, and the SR.177 that was developed from it, were military interceptor aircraft from the 1950s that due to the performance of early turbojet engines used a mixed jet and rocket propulsion to quickly gain height and close the distance on approaching enemy aircraft, assumed to most likely be Soviet bombers carrying a nuclear bomb, before using the jet engine to get back home. For the SR.177 with improvng turbojets the aircraft relied on them to gain height and do most manoeuvres using the rocket to close the distance with the intruders. Neither model entered service, although two SR.53 prototypes flew, due to a combination of improved surface-to-air missiles, improved turbojet designs with increased power outputs and fuel efficiency, and the maturing of afterburner technology, that saw aircraft like the English Electric Lightning and Dassault Mirage III being built.
Now I've always had a soft spot for the SR.53 due to its interesting engineering so I was idly wondering how early do people think it would have to be able to enter service to actually see it do so? The Lightning entered service in late 1959 so that's the obvious cut-off point. I'm thinking you'd need to see the SR.53 or SR.177 in general use by say 1954 for a minimum lifespan to justify the purchase.