Unearthed: Secrets of the devastation caused by Grand Slam, the largest WWII bomb ever tested in the UK

The Barnes Wallis creation left a hole 70ft deep and 130ft wide - now hi-tech methods are revealing just how far the devastation spread

Archaeology Correspondent

The final secrets of Britain's largest-ever conventional weapon of war are being 'unearthed' by archaeologists.

Geophysics experts are using ground-penetrating radar and other high tech methods to 'x-ray' the ground, in a remote area of the New Forest in Hampshire, to shed new light on the most powerful top secret World War Two weapon test ever carried out in the UK.

The weapon - a bomb designed by the British aircraft and munitions inventor, Barnes Wallis, and codenamed 'Grand Slam' - was almost 26 foot long and weighed 22,000 pounds, substantially bigger than any other wartime explosive device ever developed by Britain.

The New Forest test is historically important because it heralded an expansion in the crucial strategic air offensive against key infrastructure targets in Nazi Germany. The first RAF bomber command Grand Slam sortie got underway within hours of the successful test of the bomb.

Four geophysical techniques - ground penetrating radar, magnetometry, electrical resistivity and electrical resistivity tomography - are being used by the archaeologists to assess the damage done to the large concrete target building which has lain buried under a vast mound of earth for the past 66 years.

Barnes Wallis' Grand Slam bomb was designed to seriously damage and destroy buildings, bridges, viaducts and other structures without necessarily having to achieve a direct hit against them. It worked by creating a severe yet localized artificial earthquake.

The one and only test of the bomb took place on 13 March 1945. The weapon was released from a specially adapted Lancaster bomber flying at 16,000 feet over the River Avon just east of the Hampshire town of Fordingbridge, almost two miles west of the New Forest target building. Half a minute after release, the bomb, with its specially designed aero-dynamic fins, hit the target area at more than 700 miles per hour.

The crater which Grand Slam created in the New Forest on 13 March 1945 - with the target building in the background The 70 ft deep and 130 ft diameter crater which Grand Slam created in the New Forest on 13 March 1945 - with the target building in the background (Crown Copyright) Penetrating deep into the ground it produced, after a predetermined nine second interval, a massive explosion which generated the desired artificial earthquake - and created a 70 foot deep 130 foot diameter crater. It was the biggest bomb ever dropped on Britain before or since.

The geophysical investigation and the research operation in the National Archives are expected to reveal just how much damage the earthquake effect had on the target building - but oral history research recently carried out by the New Forest archaeological team suggests that the entire structure was seen to physically move when the bomb exploded some 250 feet away.

After the New Forest test, Grand Slam bombs were used between 14 March and 19 April, 1945 against nine strategically important German targets including the Schildesche railway viaduct near Bielefeld, the Arnsberg railway viaduct, the Nienburg railway bridge, submarine pens near Bremen and German gun batteries on the island of Heligoland.

The Grand Slam campaign played a key role in helping to speed up the defeat of German forces in the final two and half months of the war. Almost 100 Grand Slam bombs were produced of which 42 were used in nine major Bomber Command sorties. Today only five publicly accessible examples survive - in the RAF Museum in north-west London, Brooklands Museum in Surrey, Dumfries and Galloway Aviation Museum, the Battle of Britain Memorial Flight Visitor Centre at RAF Coningsby in Lincolnshire and Kelham Island Museum, Sheffield.

The New Forest National Park Authority's current geophysical survey and historical investigation into Grand Slam is part of a wider project researching and surveying the park's often unappreciated wartime role. Quite apart from Grand Slam, the New Forest was used as a test site for the first Barnes Wallis bouncing bombs, the development of the 'Tallboy' predecessor of Grand Slam, as well as early demonstrations of the Churchill tank. The forest was also home to nine wartime airfields, many of which played a key role in D-Day.

September 1977: The British aviation engineer Sir Barnes Neville Wallis (1887 - 1979), inventor of the bouncing bomb that destroyed the Ruhr dams, of the Wellington bomber, and of the Grand Slam bomb (Getty Images) September 1977: The British aviation engineer Sir Barnes Neville Wallis (1887 - 1979), inventor of the bouncing bomb that destroyed the Ruhr dams, of the Wellington bomber, and of the Grand Slam bomb (Getty Images) The vast concrete bunker which formed the centre of the Grand Slam target area had originally been built in 1941.

Up till now, historians had thought that it was constructed as a replica enemy submarine pen complex - so as to develop bomb strategy against such targets along occupied Europe's coastline.

However, a series of once-secret documents found in the National Archives by the New Forest National Park research team over the past year have now revealed that the building was originally constructed as a test structure to help develop more effective public air raid shelters.

It appears to have been experimentally constructed out of successive layers of different types of concrete - designed to inhibit the transmission of shock-waves through its walls and roof.

The researchers have even found a previously unknown plan of the building, showing the points at which test detonations were carried out on its roof to assess the effectiveness of the newly developed experimental multi-layer air raid shelter technology.

Bizarrely, Barnes Wallis had actually designed Grand Slam back in 1940 - but political disinterest, bureaucratic obstacles and weapon delivery problems conspired to prevent its final development until early 1945.

"Our geophysical and historical research is helping us to more fully understand and appreciate the testing of Grand Slam - and the New Forest's more general major, yet little known, role in World War Two," said James Brown, an archaeologist at the New Forest National Park Authority.

For more information, click HERE

Susan Sarandon described David Bowie as
peopleSusan Sarandon reveals more on her David Bowie romance
sportDidier Drogba returns to Chelsea on one-year deal
Arts and Entertainment
The Secret Cinema performance of Back to the Future has been cancelled again
Have you tried new the Independent Digital Edition apps?
ebookA unique anthology of reporting and analysis of a crucial period of history
Arts and Entertainment
Christian Grey cradles Ana in the Fifty Shades of Grey film
filmFifty Shades of Grey trailer provokes moral outrage in US
Louis van Gaal would have been impressed with Darren Fletcher’s performance against LA Galaxy during Manchester United’s 7-0 victory
The new dawn heralded by George Osborne has yet to rise
voicesJames Moore: As the Tories rub their hands together, the average voter will be asking why they're not getting a piece of the action
Dejan Lovren celebrates scoring for Southampton although the goal was later credited to Adam Lallana
newsComedy club forced to apologise as maggots eating a dead pigeon fall out of air-conditioning
Arts and Entertainment
Jo Brand says she's mellowed a lot
tvJo Brand says shows encourage people to laugh at the vulnerable
Life and Style
People may feel that they're procrastinating by watching TV in the evening
Rhys Williams
commonwealth games
Isis fighters travel in a vehicle as they take part in a military parade along the streets of Syria's northern Raqqa province
Arts and Entertainment
Southern charm: Nicolas Cage and Tye Sheridan in ‘Joe’
filmReview: Actor delivers astonishing performance in low budget drama
Life and Style
fashionLatex dresses hit the catwalk to raise awareness for HIV and Aids
Travel Shop
the manor
Up to 70% off luxury travel
on city breaks Find out more
Up to 70% off luxury travel
on chic beach resorts Find out more
sardina foodie
Up to 70% off luxury travel
on country retreats Find out more
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Senior Risk Manager - Banking - London - £650

£600 - £650 per day: Orgtel: Conduct Risk Liaison Manager - Banking - London -...

Commercial Litigation Associate

Highly Attractive Package: Austen Lloyd: CITY - COMMERCIAL LITIGATION - GLOBAL...

Systems Manager - Dynamics AX

£65000 - £75000 per annum + Benefits: Progressive Recruitment: The client is a...

Service Delivery Manager (Software Development, Testing)

£40000 - £45000 per annum: Ashdown Group: A well-established software house ba...

Day In a Page

Finding the names for America’s shame: What happens to the immigrants crossing the US-Mexico border without documents who never make it past the Arizona desert?

Finding the names for America’s shame

The immigrants crossing the US-Mexico border without documents who never make it past the Arizona desert
Backhanders, bribery and abuses of power have soared in China as economy surges

Bribery and abuses of power soar in China

The bribery is fuelled by the surge in China's economy but the rules of corruption are subtle and unspoken, finds Evan Osnos, as he learns the dark arts from a master
Commonwealth Games 2014: Highland terriers stole the show at the opening ceremony

Highland terriers steal the show at opening ceremony

Gillian Orr explores why a dog loved by film stars and presidents is finally having its day
German art world rocked as artists use renowned fat sculpture to distil schnapps

Brewing the fat from artwork angers widow of sculptor

Part of Joseph Beuys' 1982 sculpture 'Fettecke' used to distil schnapps
BBC's The Secret History of Our Streets reveals a fascinating window into Britain's past

BBC takes viewers back down memory lane

The Secret History of Our Streets, which returns with three films looking at Scottish streets, is the inverse of Benefits Street - delivering warmth instead of cynicism
Joe, film review: Nicolas Cage delivers an astonishing performance in low budget drama

Nicolas Cage shines in low-budget drama Joe

Cage plays an ex-con in David Gordon Green's independent drama, which has been adapted from a novel by Larry Brown
How to make your own gourmet ice lollies, granitas, slushy cocktails and frozen yoghurt

Make your own ice lollies and frozen yoghurt

Think outside the cool box for this summer's tempting frozen treats
Ford Fiesta is UK's most popular car of all-time, with sales topping 4.1 million since 1976

Fiesta is UK's most popular car of all-time

Sales have topped 4.1 million since 1976. To celebrate this milestone, four Independent writers recall their Fiestas with pride
10 best reed diffusers

Heaven scent: 10 best reed diffusers

Keep your rooms smelling summery and fresh with one of these subtle but distinctive home fragrances that’ll last you months
Commonwealth Games 2014: Female boxers set to compete for first time

Female boxers set to compete at Commonwealth Games for first time

There’s no favourites and with no headguards anything could happen
Five things we’ve learned so far about Manchester United under Louis van Gaal

Five things we’ve learned so far about United under Van Gaal

It’s impossible to avoid the impression that the Dutch manager is playing to the gallery a little
Screwing your way to the top? Good for Lana Del Rey for helping kill that myth

Screwing your way to the top?

Good for Lana Del Rey for helping kill that myth, says Grace Dent
Will the young Britons fighting in Syria be allowed to return home and resume their lives?

Will Britons fighting in Syria be able to resume their lives?

Tony Blair's Terrorism Act 2006 has made it an offence to take part in military action abroad with a "political, ideological, religious or racial motive"
Beyoncé poses as Rosie the Riveter, the wartime poster girl who became a feminist pin-up

Beyoncé poses as Rosie the Riveter

The wartime poster girl became the ultimate American symbol of female empowerment
The quest to find the perfect pair of earphones: Are custom, 3D printed earbuds the solution?

The quest to find the perfect pair of earphones

Earphones don't fit properly, offer mediocre audio quality and can even be painful. So the quest to design the perfect pair is music to Seth Stevenson's ears