Debates about the BBC’s role were just as volatile in the 1940s as they are today: Bernard Montgomery called it ‘the fourth arm of war’ while Winston Churchill labelled it ‘the enemy within the gates’. In this two-part series, Jonathan Dimbleby uncovers the story of how the BBC fought Hitler – and Whitehall – with a unique insight into one of the story’s leading players – his father, Richard Dimbleby. 　　At the outbreak of war, the BBC was very nearly shut down but Dimbleby reveals how the success of Nazi Germany’s propaganda broadcasts – listened to by up to six million at home - goaded it into action. Though the BBC had no newsgathering capability before the war, Richard Dimbleby was among the pioneers who overcame heavy censorship to bring the sounds of war into homes with the first battlefield recordings. The BBC became a powerful force for resistance in Europe and a key means of coded communication with resistance groups. And where before the BBC’s idiom had been universally ‘RP’, resolutely Northern voices like those of JB Priestley and Wilfred Pickles were deployed to universal acclaim. 　　Even at the end of the war, battles were still being fought about what to broadcast. It was only Richard Dimbleby’s threat to resign that caused his unflinching report from the Belsen concentration camp to be allowed on air.