The RAF Allied bombing campaign was heroic but controversial for one reason

One night, at the height of the Blitz, senior RAF officer Arthur Harris stood with several colleagues on the roof of the Air Ministry and watched with appalled fascination as the Luftwaffe's bombers pounded the East End of London. With the flames lighting up the night sky and the sound of explosions echoing across the capital, Harris felt moved to quote from the Bible. "They are sowing the wind, and they will reap the whirlwind," he said defiantly.

Those words may have sounded like an empty boast in December 1940, when Britain was under relentless aerial attack from the Reich, but the prophecy of Harris was to be dramatically fulfilled.

During the last three years of the conflict the RAF mounted a campaign of ever greater ferocity against Nazi Germany, destroying its industrial capacity, wrecking its transport networks, obliterating its cities and demoralising its population.

Harris himself, who became head of Bomber Command in February 1942, played a central role in the ruthless use of strategic bombing to achieve the Allied victory. Never squeamish about his mission, he told the Air Staff: "What we need to do, in addition to the horrors of fire, is to bring masonry crashing down on top of the Boche, to kill the Boche and to terrify the Boche."

In December 1940, however, Britain lacked the planes and weaponry for the task. The RAF had neither a four-engined bomber, nor practical navigation aids, while its explosive shells were prone to detonation failure. The irony of this catalogue of chronic inadequacy was that the air establishment had always clung to the theory that strategic bombing was the real purpose of the RAF, not Army co-operation or maritime support or fighter defence.

"Our belief in the bomber was intuitive, an article of faith," wrote Sir John Slessor, the RAF's Director of Plans. Yet the politicians and air chiefs had failed to will the means to achieve this end. The weakness of Bomber Command was highlighted in a crucial report commissioned by Downing Street in mid-1941 which found just a tenth of Bomber Command's sorties came within five miles of their target - and half of their bombs fell in open countryside.

Drastic change was clearly needed and, thanks to Churchill's impetus, it came quickly. Bigger and better bombs were made available. Navigation was revolutionised by the introduction of airborne radar and ground-mapping technology, as well as the creation of an elite "Pathfinder" force which used flares and incendiaries to illuminate a target for the bombers that followed.

Two other developments in early 1942 really transformed the RAF's potency. One was the arrival of the magnificent Avro Lancaster, which turned out to be the greatest heavy bomber of the war. Other new aircraft had entered Bomber Command's service by then, among them the rugged four-engined Handley-Page Halifax and the elegant twin-engined De Haviland Mosquito, renowned for its speed and unique wooden construction.

But it was the Lancaster that inflicted the worst damage on the Reich with its agility and huge loading capacity. On average, it carried 12,000 pounds but towards the end of war it proved capable of lifting the colossal 22,000lb Grand Slam bomb. Even with this strength it was fast and manoeuvrable. Harry Yates of 75 Squadron recalled: "Everything about it was just right. It flew with effortless grace and had a precise, weighted feel. It made the pilot's job easy."

In addition to the Lancaster, Bomber Command gained a new chief in Harris, who brought an uncompromising sense of purpose to his position. The son of an engineer in the Indian Empire, he learnt self-resilience in his lonely, isolated childhood at boarding schools in England and then as a farmer in Rhodesia before serving as a pilot in the Royal Flying Corps during the First World War.

Having witnessed the mass slaughter on the Western front, he loathed the idea of another land campaign on the continent, hence his belief that bombing alone could win the war. He immediately made his presence felt by launching a series of "Millenium raids" on German cities. These were designed to show the power of Bomber Command by the creation of a vast aerial armada, made up of more than 1,000 planes for each assault.

There was a slightly makeshift quality about these raids, whose publicity value was greater than the real damage caused. But Churchill was gratified to see Britain go on the offensive for the first time.

Indeed, the political climate was now far more conducive to the bomber war. From mid-1942 the Russians, along with influential voices in Britain, were demanding the Allies open up a second front in Western Europe to relieve pressure in the East.

It was an unrealistic call since preparations for an Allied invasion had only just begun. But the Allied aerial offensive enabled Churchill to tell Stalin that a second front had effectively been opened in the skies over Germany.

The bombing campaign dramatically increased in intensity in 1943, following the Casablanca conference between Churchill and Franklin Roosevelt, where it was agreed to conduct round-the-clock bombing of Germany, with the RAF still operating at night and the US Army Air Force carrying out daylight operations in Boeing B-17 Flying Fortresses - increasingly under the protection of the superb long-range P-51 fighters' escorts.

Buttressed by deepening experience and better equipment, Bomber Command reached new levels of devastation, as typified by the sustained attack on Hamburg at the end of July, which killed 45,000 people - the vast majority of them women and children - while a further 1.2 million traumatised refugees fled the city.

Harris believed the campaign of demolishing German cities was the prime reason for Bomber Command's existence. He dismissed other objectives, such as oil refineries, transport hubs and U-boat bases, as "panacea targets". In that vein, he had no time for the RAF's most daring exploit of the war: the Dambusters raid of May 17, 1943, which he described as "the maddest proposition I have ever come across".

But he sometimes had to bow to his superiors, as in this case and other precision raids, like the attack by 600 heavy bombers on the research facility at Pennemunde, which drastically put back the German rocket programme, or the assault on the French railway system in early 1944 to hinder the movement of German reinforcements come D-Day.

Strategic bombing was undoubtedly the most dangerous Allied undertaking in the entire war. Of the 125,000 men who served in the Command, more than half were killed in action. There were few more terrifying combat experiences in the European war than to be in a Lancaster on a bombing run under the deadly attention of German fighters, anti-aircraft guns and searchlights. One airman described it as "entering the jaws of hell".

Yet the bomber crews were often distinguished by their almost superhuman bravery, as reflected in the 19 Victoria Crosses won in their Command. Guy Gibson, leader of the Dambusters, and Leonard Cheshire, who flew more than 100 missions, were two of the most famous recipients. But another astonishing case was that of Norman Jackson, an engineer with 106 Squadron, whose Lancaster was hit during a raid on Sweinfurt in April 1944.

Despite severe shrapnel wounds in his legs, he climbed out on to his Lancaster's starboard wing to extinguish an engine fire, only to lose his grip when the bomber came under renewed German attack. But he managed to pull the ripcord of his parachute as he fell to earth, where he was soon captured and ended up as a prisoner-of-war.

Because of the civilian death toll in Germany, which some estimates put at over 900,000, the Allies' bombing campaign has long been enveloped in controversy. Condemnation of the RAF has often crystallised around the destruction of Dresden in February 1945, when 25,000 people perished. But raids like that shattered the German war machine. Petrol ran out, factories were paralysed.
Thanks to the RAF's heavy bombers, the Reich was forced to divert colossal resources into air defences.

By 1944, two million Germans were engaged in anti-aircraft duties while a third of all artillery production was devoted to anti-aircraft guns when such weaponry was in desperately short supply on both eastern and western fronts.

The air campaign also meant deepening misery, food shortages and sleep deprivation for Germany's population. Alternatively, it brought hope to the victims of German tyranny. Ben Halfgott, a Jew imprisoned in a concentration camp near Dresden, recalled: "It was glorious, for we knew that the end of the war must be near and our salvation was at hand."

Leo McKinstry is the author of Spitfire, Hurricane and Lancaster, all published by John Murray in paperback and e-book