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 : I am aware of the operational difference between a ramjet and a scramjet; my point was that I had understood that the term ""ram accelerator"" covered cannons that operated both in subsonic and supersonic combustion regimes (among other things, this is what that Discover article you mention described). I had never heard the term ""scram accelerator"", and the description on the combustion modes page you link doesn't mention it either, which makes me leery of considering it a technical term. Google turns up a handful of hits for papers that used it, but ""ram accelerator"" is far more common. Please don't take this as an attack; it just strikes me as a term that is not in common use among academics discussing this type of device."