"The production of the overseas cap for the American Expeditionary Forces was likewise an extensive undertaking. When the requisition for overseas caps came from France, it was not possible to design one here because of a lack of knowledge as to what was required... As soon as [a] sample was received a meeting of cap makers was called in New York, and 100 manufacturers attended. One and all agreed to turn over their factories to the exclusive production of overseas caps until all requirements were met. It took these cap makers only two weeks to to turn out the first order. In all 4,972,000 caps were delivered."
The concluding paragraph contains more venomous comments as to what these American milliners thought of the lid.
From Amazon: America's Munitions, 1917-1918.