Ram-jets in Great Britain have, until now, been associated with Guided Missiles and, for this reason, tight security regulations have been in force. In fact, it is only recently that it has been possible to talk about ram-jets at all. Even now, quite a number of features in these engines are classified and, for this reason, some portions of this paper may appear perhaps a little thin and inconclusive, but I have done my best to discuss the subject as fully as possible.

It is now generally known that the work of the Bristol Company has led to the adoption of the Thor ram-jet engine for production by the Ministry of Supply but security restrictions remain and in this lecture I have drawn upon general experience and thoughts in this field and avoided giving information directly related to a particular engine. In these circumstances, of course, the choice of any operating condition for the purpose of giving form to the lecture has had to be a purely arbitrary one.