The present time, when the prospect of high speed flight often seems to recede, not to approach, may well be a good occasion to review the ram-jet, an engine whose main use is at high flight speed. We owe the succinct name “ ram-jet” to the Americans and the original idea to the French. But despite the admirable efforts abroad this paper is most concerned with British ideas, especially and naturally with those conceived and prosecuted at the National Gas Turbine Establishment. At the outset it is appropriate to acknowledge all the separate personal contributions to the subject of this paper and the assistance of my colleagues in preparing some of the information presented.