In the literature on the emergence of the principles of war in British military thought there has been a failure to examine the reaction of the Royal Navy and the Royal Air Force to the appearance of the first list of principles in the army’s 1920 Field Service Regulations. By considering correspondence, articles, books, field manuals, and staff college lecture scripts, this article demonstrates that there was a debate on the principles of war between the world wars which involved all three armed services. The acceptance of the principles into the doctrine of each of the services represented a fundamental shift away from Jomini and the final acceptance of Clausewitzian approaches to the theory of war. The debate also contributed significantly to the emergence of a ‘common language’ between the services, thus laying the basis for a tri-service ‘strategic culture’ which was attuned to the challenges of joint operations.