In July, 1917, a new scheme for warning the people of London of impending air raids was adopted. When enemy aircraft were approaching, policemen with a notice warning passers-by to "take cover" went out on bicycles, blowing their whistles to attract attention. When all danger had passed, Boy Scouts went round blowing bugles.
Caption and image source: Hamilton Fyfe, 'Might and menace of raiding giants', in John Hammerton, ed., War in the Air: Aerial Wonders of our Time (London: Amalgamated Press, n.d. [1935?]), 344.
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