The Dambusters by John Sweetman, David Coward and Gary Johnstone (timewarner, £15)

THE Dambusters accomplished one of Britain's most celebrated feats of arms against the Nazi regime during the Second World War.

The daring raid by RAF Lancaster bombers on hydro-electric dams in the Ruhr - the industrial heartland of Germany - has entered British folklore.

Aeronautical engineer Barnes Wallis, who built the R100 airship at Howden, near Goole, and has a display devoted to his extraordinary career at the Yorkshire Air Museum, Elvington, was the genius behind Operation Chastise. He designed the "bouncing bombs" that demolished the Mohne and Eder dams on the night of May 16-17, 1943.

The heroism of the bomber crews, led by Wing Commander Guy Gibson, who was awarded the Victoria Cross for his part in the raid, was portrayed in the popular film, The Dam Busters.

The 1954 box-office hit, starring Richard Todd as Gibson and Michael Redgrave as Barnes Wallis, is widely regarded as the authentic version of events, although it contains many factual errors.

Now, to mark the 60th anniversary of the raid, Dambuster expert John Sweetman has written an authoritative account to correct some of the myths surrounding the operation.

Sweetman stresses that the chances of failure were high. Time was against the Dambusters. Once the plan was approved, the men of the newly-formed 617 Squadron had barely seven weeks in which to hone their skills, using a revolutionary weapon that was not fully tested until four days before take off.

There was one short opportunity for attack - in May 1943 when water levels in the dams were at their highest. If the attack had failed, it could not have been followed up for another year - or possibly ever again.

The raid was a tonic to war-torn Britain and her allies, particularly in the United States where President Roosevelt was being urged to concentrate the country's war effort in the Pacific, against Japan, rather than in Europe against Hitler.

The operation's international impact was immense as aerial photographs of the shattered dams haemorrhaging millions of tons of water were flashed around the world.

Despite that initial euphoria, revisionist historians went on to dismiss Bomber Command's most famous operation as a "publicity stunt", a "misconceived concept", "not worth a single aeroplane" and having "a negligible effect on the German war effort".

617 Squadron certainly paid a heavy price. Excluding the three Lancasters that aborted the operation, half of the airmen in the remaining 16 aircraft did not return: 53 were killed and three were taken prisoner.

Sweetman concedes that the effect of the raid may have been exaggerated by the media after the operation; but he argues that it was still worthwhile. He points out that waterworks serving the Ruhr coalfield were out of action for four months and water levels in the reservoirs were reduced in case of another attack.

Much of the flooded land below the Mohne and Eder dams could not be tilled for years, leading to food shortages.

A division of soldiers and their flak guns were deployed to protect the Ruhr dams, leaving German towns and cities less well defended against the increasingly heavy Allied bomber raids.

The Dambusters by John Sweetman, David Coward and Gary Johnstone (timewarner, £15) is published tomorrow. The book ties in with a two-part series on Channel 4 featuring modern RAF personnel being trained to emulate their 1943 predecessors by undertaking the Dambusters raid, using a computer simulator.

Updated: 10:26 Wednesday, April 16, 2003