In the past, the majority of civil aircraft have been powered by engines which have been developed primarily for the Royal Air Force. Their development costs have been borne by the Service departments, and then they have been converted for civil use at comparatively small extra cost.

It has always been questionable whether these converted engines have been really suited to their civil role, and it will become even more doubtful the farther the design and performance of civil aircraft depart from those of military aircraft.

In this paper, an attempt has been made to coyer the more important requirements for the two kinds of engines, and to see how they compare. If it appears that too little has been said concerning the gas turbine, that is because there is as yet no experience of its commercial operation.

The opinions expressed in the paper are the author’s and have no official significance.