This object is a large air raid siren. It was mounted on the roof of Kingston Police Station in Portsmouth during the Second World War.
It was sounded to warn local people when enemy aircraft were approaching.
Portsmouth suffered many air raids during the war largely due to enemy attempts to target the Dockyard. As a result large parts of the city were devastated.
The siren was kept in place into the 1980s, as part of a nationwide nuclear attack warning system.
There were also smaller types of mobile air raid sirens which were used indoors in factories.
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