The War Illustrated, Volume 1, No. 1, Page 6, September 16, 1939.

Half an hour after the war began, Britain received her first air raid warning. Everywhere in London and the southern and eastern counties the sirens wailed their note of warning.

Surprised and hardly believing, the people listened. There was not the slightest sign of panic. The Air Raid Wardens repeated the warning on their whistles, and the people proceeded at once in the most orderly fashion to their shelters. Auxiliary firemen put on their uniforms in readiness for any emergency.

In a few minutes the "All Clear" was sounded, but it was only some hours later that the Air Ministry announced that a strange aircraft had been observed approaching the south coast, and as its identity could not be readily determined, the air raid warning was given. It thus provided excellent practice so that further warnings were received with the same sang-froid.