The first full year of hostilities in WWII brought a renewed threat to the BBC's independence.

The BBC had made no attempt to hide any bad news - of which there was plenty in the early days of 1940. The Admiralty was soon accusing it of "unrelieved pessimism" over its reports of Britain's losses at sea.

Churchill became the prime minister of a national government in May 1940 - and described the BBC as "the enemy within the gates, doing more harm than good".

The broadcasters were only too aware of the stance taken by Churchill during the general strike - when he had wanted to annexe the BBC. But again he held off. Most of the audience would have been far more aware of the changes happening on air.

The number of daily bulletins had gone up to ten but gradually, the number was reduced, eventually to six. It was the nine o'clock evening bulletin that provided a focus for the nation - "almost as sacrosanct as family prayers are said once to have been", according to historian of the BBC, Asa Briggs.

Audiences regularly numbered sixteen million - half the adult population.

The bulletins were also changing fundamentally. The formal weather forecasts disappeared altogether - to avoid giving help to enemy planes.

And for the same reason, every effort was made to eliminate any casual mention of the weather in other news stories - a problem especially in sports coverage. The news was also kept vague, at the government's insistence. For example, an air-raid might be said simply to have caused "a number of casualties - some fatal" or its target might be described only as "the south coast".

As was pointed out, while the policy did mean the bulletins were less informative to the enemy, they were also more worrying for many of the home audience.

But there was still an expectation that traditional BBC objectivity would be maintained. A broadcast on an aerial dogfight off Dover scandalised some such as "We've just hit a Messerschmitt! Oh, that was beautiful!" and "Oh boy, I've never seen anything as good as this!" A retired major-general wrote to the Times to condemn it as "an insult to a civilised society".

It was not only the BBC's correspondents who found themselves in the front line in WWII. There was no escape for many of those who had stayed behind in London.

The Broadcasting House newsroom had been moved to the basement when the London Blitz began in September 1940. The building was protected by concrete blocks, sandbags and armed guards. But this was no defence when BH took a direct hit from a delayed-action German bomb on 15 October 1940.

It came to rest in the music library on the fifth floor - not far from the editorial team looking after the monitoring service. The bomb eventually exploded as attempts were being made to push it outside. Seven people were killed - including four of the monitoring group.

Listeners at home heard just a dull thud - as Bruce Belfrage was reading the nine o'clock news. Belfrage carried on as though nothing had happened - despite being covered with plaster and soot.

In a studio nearby, another bulletin was going out, on the German Service. Again, the audience would have been unaware that anything was wrong - although several studios were wrecked.

Less than two months later, on 8 December, BH again suffered extensive damage when a landmine exploded in Portland Place - killing a policeman.

Within an hour of the explosion, the BBC's European operation was broadcasting from emergency studios at a disused ice-rink in Maida Vale. A bulletin in Norwegian was the only one to be lost.

In April 1941, a member of BBC staff was killed when bombs brought more devastation to buildings around BH. Less than a month later, a member of the German Service died when the Maida Vale studios took a direct hit.

The summer of 1940 brought an end to the BBC tradition of nameless newsreaders - at least for a time. The BBC explained that, in wartime, listeners "must be able to recognise instantly the authentic voice of BBC broadcasting".

It was on the lunchtime news of 13 July 1940 that Frank Phillips became the first reader to identify himself. But concern persisted that, named or not, the newsreaders all sounded the same - and it wouldn't be too hard for the Germans to imitate them.

The result was the appointment to the newsreading team of Yorkshireman Wilfred Pickles - the "Have a Go" host in later years. He made his debut in November 1941 - and became an instant hero to many listeners when he ended the midnight news by wishing his fellow northerners "Good neet".

The year 1941 also saw the start of the BBC's V For Victory campaign. It began in January - initiated by the Belgian Service, and encouraged by the editors in charge of news broadcasts to Europe.

Listeners were asked to demonstrate their support for the Allies by chalking up the letter V wherever and whenever they could. It stood for "victory" in both French (victoire) and Flemish (vrijheid). The call was taken up enthusiastically not only in Belgium - but in France, the Netherlands and beyond.

Next came the realization that the three short notes and one long at the start of Beethoven's Fifth echoed the Morse code for "victory". The V sound on drums immediately became the call sign of all the BBC's European services.

The Germans responded by trying to adopt the V for themselves, as representing "the old German war cry, 'Viktoria'". The BBC campaign was terminated in May 1942.

On 17 March 1941, the European Service left Maida Vale for Bush House, in Aldwych, the building that remains the home of the World Service.

In July 1944 a V1 flying-bomb landed outside the building. Many people were badly injured - including several members of the European Service.

There can be no doubt that the BBC's news broadcasts to Europe - and beyond - played a critical part in the struggle against the Axis powers.

Huge audiences listened in - sometimes under threat of death. A relative unknown by the name of General de Gaulle made frequent rallying-calls from London to the people of France. In his memoirs, he praised the British for their success in understanding and exploiting "the effect which a free radio was capable of producing upon imprisoned people".

A girl who escaped from Czechoslovakia wrote to the BBC, to say that people who were "almost too poor to buy bread" now had a radio; they believed London was "the only place to feed the soul".

The daily audience in Germany itself for BBC broadcasts is estimated eventually to have reached at least ten million - and perhaps half as many again.

The BBC's philosophy in its reporting had been spelt out in the early days of constant setbacks for British forces. "What we have to do in this period of war when we're on the defensive is to establish our credibility," said the European Service news editor, Noel Newsome. "If there's a disaster, we broadcast it before the Germans claim it, if we possibly can. And when the tide turns and the victories are ours, we'll be believed."

It was a policy that paid dividends. In 1943, the historian GM Young said the BBC's news broadcasts had given it "a standing without rival on the European Continent." Not long afterwards, the writer George Orwell wrote that saying "I heard it on the BBC" was almost the same as saying "I know it must be true".

A BBC engineer who was taken prisoner by the Japanese said the news bulletins from London had been "the only thing that gave us something to live for".

Just after half past nine on the morning of 6 June 1944, the familiar voice of John Snagge announced on BBC radio that D-Day had begun. This was the start of the Allied invasion of German-occupied Europe.

That evening, the nine o'clock news was followed by the first edition of "War Report". It was a revolutionary concept: a half-hour programme designed to bring the "latest and fullest picture of the war" into the nation's living-rooms.

The new programme was almost a military exercise in itself. Correspondents had been trained to read maps and identify aircraft; they had been subjected to assault courses; they had taken part in exercises with live ammunition.

The key was the use of on-the-spot recordings. These were nothing new to the audience but the introduction of a new "midget" recorder was critical. It was like a wind-up gramophone, recording on discs that lasted two minutes. It weighed about 30lbs (more than 13kg). And it gave the BBC correspondents a new freedom.

The day before D-Day, Godfrey Talbot set the mood for the months ahead when he reported on the liberation of Rome: "My battledress is torn with the violence of this welcome," he said. "My jeep is half-full of roses."

There were to be many more broadcasts that captured the sounds and the drama of warfare as never before.

After the Battle of Arnhem, in September, Stanley Maxted told of the "nightmare" of trekking for hours through mud and rain, machine-gun tracers skimming overhead. "Day or night, the shelling and mortaring never stopped," he said.

And in April 1945, Richard Dimbleby shocked the world with the horror of Belsen: "The dead and the dying lay close together. I picked my way over corpse after corpse... ." At first the BBC refused to broadcast Dimbleby's Belsen despatch.

There were accusations later that the Corporation had played down the holocaust. But others have argued that editors were hesitant - because the truth was almost beyond comprehension. In any case, the report was broadcast, twenty-four hours later - after Dimbleby had threatened to resign.

War Report was eventually taken off air in May 1945 - the day after the German surrender. It had run to 235 editions and had carried almost two thousand despatches. Two of its correspondents, Kent Stevenson and Guy Byam, had also been killed.

BBC News emerged from WWII with its reputation vastly enhanced. News bulletins were widely believed to have been fundamental to the morale of the troops.

It was a "big factor", said writer and broadcaster Desmond Hawkins, "the huge difference between the First and the Second World War".

Audiences, at home and abroad, had had a taste of foreign propaganda - such as the broadcasts from Germany of "Lord Haw-Haw" (William Joyce). News bulletins on German radio had been crudely partisan. Phrases like "the shameless lying of the criminal Churchill" were typical.

At home there had been the occasional lapse from BBC objectivity. Alvar Lidell had once begun a bulletin about Montgomery's success at El Alamein by saying: "I'm going to read you the news - and there's some cracking good news coming... " And there had been the occasional charge of suppression.

However a leading Czech politician felt able after the war to salute the BBC for having "educated the public without ever lowering itself to a mere instrument of propaganda".

In the process, the nature of the news operation had itself been transformed. Many changes were evident on air. But, behind the scenes, large numbers of newspaper journalists had been recruited to challenge the BBC's ways of doing things. The new arrivals helped to "kick out the stuffiness," according to former war correspondent Frank Gillard.

Throughout the conflict, BBC News had also gained enormously from the expertise of the Monitoring Service. The monitors had succeeded in capturing the war's "immediacy, its intricacy, its subplots and its surprises", wrote the BBC's historian, Asa Briggs.

Overall, the BBC emerged in 1945 as the world's leading international broadcaster. It had gone into the war broadcasting in seven foreign languages. It came out of it broadcasting in 45.

The world's longest-running speech radio programme took to the airwaves on 24 March 1946. It was called Letter from America and would be presented by Alistair Cooke for the next 58 years until his retirement in March 2004.

Cooke, who was born in Salford, had done something similar for the BBC in the past. First, after emigrating to the United States in 1937, he reflected on the American way of life in a series called Mainly About Manhattan. Then, during the war, Cooke was involved with a very successful programme called American Commentary.

Because money was short, Letter from America was commissioned initially for 13 weeks only - with a promise of a further 13, if it happened to be "a wild success". Well over half-a century later, it continued to be an audience favourite. Cooke remained at the helm: a "living archive of America and British history", according to one critic.

Cooke put his success down to his ability to write a script that is designed to be spoken - rather than read. The trick is "putting it on the page in the syntactical break-up and confusion that is normal talk," he says. "No matter what you're talking about - gardening, economics, murder - you're telling a story. If you say a dull sentence, people have a right to switch off."

The verdict is endorsed by Cooke's biographer, the World At One's Nick Clarke. Cooke had "the most lucid of writing styles, a remarkable breadth of knowledge stored in a fine memory-bank", says Clarke. Add to that "a story teller's ability to build up suspense and artistic tension", he argues, and "listeners are drawn in, seduced and finally satisfied".

Alistair Cooke was awarded an honorary knighthood in 1973. He died, aged 95, on 29 March 2004, at his home in New York.

The programme acknowledged as the forerunner of BBC TV news made its debut in January 1948. Viewers keen to have some sort of news service had already waited more than 18 months since TV returned to their screens, after the wartime shutdown. So it was perhaps no surprise that Television Newsreel was an instant success.

It was based on the cinema newsreels - and came under the control of the Television Service, at Alexandra Palace, rather then the news department at Broadcasting House. Indeed, the news editors in BBC radio were content to see it as entertainment - and therefore no threat to their reputation for news that was up-to-the-minute, accurate and impartial.

But increasingly, snippets of hard news began to creep into Television Newsreel. For a time, there was deadlock over the future of news on BBC television. The radio men at Broadcasting House were unwilling to be elbowed out.

It was to be another six years before there was agreement on an improved format for television news.