The devastating effects of a 22,000lb bomb used by the RAF to help end the Second World War are set to be laid bare as archaeologists investigate a remote test site in the New Forest.
The ‘Grand Slam’, which was designed to simulate the effects of an earthquake in order to cause wide-spread destruction to critical infrastructure, was Britain’s biggest conventional weapon ever.
The bomb was the brainchild of Barnes Wallis, who is best known for creating the bouncing bombs used in the famous Dambusters raids in the Ruhr Valley.
It was dropped on nine different sites in Germany in 1945 in a bid to damage morale and encourage the Nazis to surrender to Allied forces.
The target of the Grand Slam was key infrastructure, such as railway bridges and submarine bays, rather than built-up populated areas.
The bomb - which Wallis spent years developing before it was built - was tested just once, on March 13, 1945, when it was dropped close to a concrete bunker in the New Forest near the town of Fordingbridge.
It tunnelled deep into the ground at a speed of 700mph before detonating, setting off tremors which were the equivalent of an earthquake.
The crater left at the New Forest test site was 70ft deep and 130ft across, and eyewitness reports suggested that the test building could be seen shaking.
The concrete structure was originally thought to have been an imitation of a German submarine pen, but new evidence suggests that it was in fact an attempt to develop a more robust air-raid shelter, built over five and a half months at a cost of £250,000 (the equivalent of more than £10million today).
After the end of the war, the site - known as Ashley Range - was returned to its natural state, and the concrete bunker was encased in a mound of dirt because it could not be demolished.
‘The military had a responsibility to return it as found,’ New Forest archaeologist James Brown told MailOnline. ‘But there’s a lot of concrete and other structures just left out there.’
Visitors to the forest can still see huge craters, an observation shelter and chalk markings made on the ground in order to help bombers find their targets.
Now researchers from the New Forest National Park Authority hope to use modern scientific techniques to map the devastation caused by the Grand Slam in greater detail.
They will deploy ground-penetrating radar, electrical resistivity tomography and magnetometry to work out to what extent the bunker was damaged by the bomb.
Archaeologists are banned from digging near the site, because of the area’s status as part of a national park and its use as a commons for the grazing of ponies and cattle. Despite its image as a peaceful, bucolic patch of England, the New Forest was actually central to the war effort as one of the most active test sites in the country.
As well as the Grand Slam, tanks and bouncing bombs were first tried out in the forest, while the area also hosted nine air fields. Researchers hope that their hi-tech tools will enable them to reconstruct the history of the site in greater detail than ever before.
Mr Brown said the new research could help the public learn more about the role played by the forest in the war.
‘We can create 3D models of all that data that we can have people interact with,’ he said. ‘Some of our most recent history is some of our rarest - people are focussed on Bronze Age and Roman history and ignore the Second World War.
‘It’s only recently that interest in Second World War history and archaeology has picked up.’
HOW THE ‘EARTHQUAKE BOMB’ HELPED THE RAF BRING THE WAR TO AN END
The Grand Slam bomb, also known as ‘Ten Ton Tess’, was the largest conventional weapon ever to be developed by the British military.
It was designed by Barnes Wallis, inventor of the bouncing bomb used by the Dambusters, as a way of destroying key sites without having to hit them directly.
He came up with the idea at the beginning of the Second World War, but it was not until towards the end of the conflict that it finally attracted support from top brass and went into production.
The bomb was dropped from a Lancaster bomber and hit the ground at speeds of up to 700mph, tunnelling as deep as 40m into the earth.
It then detonated inside the ground after a nine-second delay, setting off huge vibrations which imitated the effect of an earthquake. This meant that structures could be damaged or even destroyed by the bomb as long as it fell within a few hundred metres.
The Grand Slam only had to be tested once, in the New Forest in March 1945 - the effect was so extreme that RAF chiefs instantly knew it was ready to be used in the air campaign against Germany.
The next day, one of the bombs was dropped on a railway viaduct in Bielefeld, causing around 100m to collapse in a bid to interrupt German transport and communications.
In total, 42 Grand Slams were deployed on nine different sites, including train bridges, gun batteries and structures housing U-boat submarines.
The use of the bomb contributed to the aerial assault on Germany which convinced senior Nazis that the war had finally been lost, leading to the final surrender in May 1945. After the end of the Second World War, there were still 57 Grand Slams left, but they would never be used in combat again.
Only five complete bombs still survive - they are on display at the RAF Museum, Brooklands Museum, RAF Lossiemouth, RAF Coningsby and the Dumfries and Galloway Aviation Museum.–Daily Mail