The radio broadcast signalling the declaration of war also meant a signal for members of the orchestra to leave their homes immediately, and head for a rendezvous from which they would be evacuated to a secret location.
Here, the orchestra would be able to continue with its duties in safety.
In the years that followed, the Orchestra, based first in Bristol and then Bedford, played an improbably important role in the British war effort, often performing under difficult circumstances.
The story of this remarkable chapter in the BBC Symphony Orchestra's history examines the logistical problems of transporting an entire artistic community to new homes, considers the remarkable artistic achievements of the orchestra during this time, and touches on some of the hilarious and absurd anecdotes of wartime orchestral life.
As listeners tuned in to the Nine O'Clock news on September 2, 1939, they heard the words 'This is London' replace the usual 'This is the BBC'.
An unsuspecting public wouldn't have realised this was a secret signal to of all people - members of the BBC Symphony Orchestra.
These unlikely contributors to the war effort immediately left their homes, met in London, and were taken to a secret destination.
No-one knew how long they'd be gone, or whether they'd ever come back.
In the dark years that followed, first in Bristol and then in Bedford, the BBC Symphony Orchestra and its conductor Sir Adrian Boult played an improbably important role in the fight against the Third Reich.