This warning signifies an air raid is likely about to take place. Raid warning: a six-second high-tone followed by a six-second low tone, with 15 cycles per period. This signifies that an air raid is imminent. Post-raid warning: a single three-minute high tone. When sounded, it signifies an end to the raid or a cool-down of the wartime situation.

All clear is the signal, generally given by an air raid siren, which indicates that an air raid or other hazard has finished and that it is safe for civilians to leave their shelters; it is commonly used in radios as well.

2018年6月6日 · This confidential early-war memo issued to Air Raid Wardens covered the various coloured warnings that were used during the second world war: Air Raid Message - Yellow: wardens to gather at their posts (public not informed) Air Raid Warning - Red: air raid imminent - wardens dash out into their their sectors blowing short blasts on their whistles

This pamphlet is furnished primarily as a guide to aid local civilian defense organizations in the proper and efficient discharge of their duties with the air raid warning service in the event of air raids, and its purpose is twofold: a) To furnish a set of instructions to local civilian defense organizations for the installation and operation ...

First is Blue Warning, a steady blast, meaning enemy planes headed in your direction. Second is Red Danger, a series of short or wavering blasts, meaning bombing expected. Third is Blue Warning again, meaning enemy planes have passed. Final line is White All Clear, a radio signal indicating danger is over.

Air-raid sirens first sounded the warning in London in September 1939. They were electric and emitted two signals: a waxing and waning warning signal and a steady tone which meant that people could come out of their hiding place.

Air Raid Warning. When the Observer Corps or Radar detected a raid the information was passed down to the local authority who sounded the air raid warning. The alert was a load siren that made a sound that rose and fell in pitch. When it was sounded people had to find shelter.

The signal for an air raid alarm is a series of short blasts from fog horns installed throughout the city, The series of blasts will continue for a period of about two minutes.

Sign, frame and slide: rectangular wooden sign (12 x 7 inches); mahogany frame enclosing vertically bisected green and red backing with inscription. A wooden slide can be moved from side to side to reveal the appropriate raid staus: 'AIR RAID' / 'ALL CLEAR' / ' WARNING'. Second World War period British Air Raid Precautions (ARP) warning sign.

To explain how the civilian air raid warning system will be coordinated with the military air-craft warning service. DEFINITIONS. Air Raid. An attack or threatened attack upon terrestrial objectives by enemy aircraft. Civilian Air Raid Warning System.