: 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.