The German metallurgists were the first to discover how to make the light alloy of aluminium which they called duralumin. I understand it is a mixture of 97 per cent aluminium and 3 per cent copper, but it may have a very small percentage of rarer metals. Whereas aluminium has a yield point of about nine tons per square inch, duralumin has a yield point of twenty-five tons per square inch.

Before and during the First World War the German aircraft constructors used duralumin in the construction of Zeppelin rigid airships, aeroplanes and seaplanes and flying boats. Towards the end of the First World War, I began to fear that the Germans would invent all-metal aircraft with highly streamlined forms which would increase the speed of their aircraft and that at very high speed with their bombing aircraft, they would fly at almost house top level, drop a time bomb on our works and be at a safe distance before the explosion occurred.