Some writers claim the Air Staff ignored a critical lesson, however: British morale did not break. Targeting German morale, as Bomber Command would do, was no more successful. Aviation strategists dispute that morale was ever a major consideration for Bomber Command. Throughout 1933–39 none of the 16 Western Air Plans drafted mentioned morale as a target. The first three directives in 1940 did not mention civilian populations or morale in any way. Morale was not mentioned until the ninth wartime directive on 21 September 1940. The 10th directive in October 1940 mentioned morale by name. However, industrial cities were only to be targeted if weather denied strikes on Bomber Command's main concern, oil.

What was the critical lesson Air Staff ignored?