"Beatrice Harrison played the cello in her garden in Foyle Riding, Surrey, regularly accompanied by nightingales. The BBC transmitted the music of Beatrice and the birds live on May 19th, 1924 – the first ever live outdoor broadcast. Each May 19th, the BBC returned to the garden to broadcast the nightingales, even after Beatrice moved house in 1936. On May 19th, 1942, as BBC engineers were recording the bird-song prior to transmission, a faint hum gradually became audible, slowly increasing in volume, as 197 bombers flew overhead on their way to raids in Mannheim. Realising the security risk, the broadcast was halted. But not the recording…"
Click on the link above to access the recording.