Archaeologists find World War II bomb testing building at Ashley Walk Bombing Range

By Culture24 Reporter | 27 January 2014

Covered up at the end of World War II, a 'Sub Pen' on a range which witnessed Britain's heaviest bomb is being rediscovered in the New Forest

A black and white photo of an earth crater caused by a bomb
The crater left by the so-called Grand Slam bomb at Ashley Walk Bombing Range© Crown Copyright
Penetrating radar, electrical tomography and gradiometers on a part of the New Forest National Park where the largest ever British bomb was dropped have revealed the buried chambers of a concrete structure built to resemble a German submarine station during the Second World War.

Ashley Walk Bombing Range is a testing site which has been the subject of repeated research. The Grand Slam bomb, a 22,000-pound weapon made by Sir Barnes Neville Wallis, the inventor of the bouncing bombs made famous by operations such as the Dam Busters attack on the Ruhr Valley, was dropped nearby on March 13 1945 – an apparently successful precursor to its use over Germany the following day, when it destroyed the Schildesche railway viaduct.

Investigators are searching for the possible remains of a two-level bomb-resistant shelter, built to withstand a direct hit from a 500-pound, “medium capacity” bomb under the orders of the Ministry of Home Security which took responsibility for air-raid shelters, wardens, provisions and rescues after 1939, including the appointment of millions of fire-watchers and the widespread distribution of gas masks.

A predictably damaging 4,000-pound bomb, dropped from 12,000 feet at a speed of 200mph, is thought to have pre-empted a raid on a similar concrete target in Germany.

Air attack threats were reduced by the end of the trials, with the tide of the war turning. Although the target was covered in earth at the end of the conflict, the tests may have contributed to Cold War intelligence.

The Ashley Walk test bombs:

Bomb No 1: A British 500lb GP Mk IV bomb filled with TNT and fused 1/10th sec nose and 1/40th tail, dropped from 12,000 feet at an air speed of 200 mph. The bomb hit the target at about 18 feet from the unsupported west edge of the roof slab.

Bomb No 2:
A British 500lb SAP Mk V bomb filled with a suitable high explosive substitute by the Royal Ordnance Factory Woolwich. It hit the target at about 15 feet from the west edge and six feet from the north edge of the roof slab. bomb showed no outward sign of damage.

Bomb No 3: An inert 500lb British SAP Mk V bomb similar to bomb No 2. It hit the north west corner of the target over the 3ft 3in thick supporting wall and broke away the concrete down to the level of the intermediate layer of slab reinforcement 2ft 6in below the top surface.

The bomb bounced off and buried itself in the earth. At the time of the report it had not been recovered and may still be there.

Bomb No 4: A German 250kg SC bomb was placed on its nose in the crater formed by bomb No 2. The German bomb was almost identical to the 500lb British bomb, with a slightly heavier charge weight (285lb versus 250lb).

Insufficient German bombs were available for actual dropping trials. The bomb was detonated electrically and the crater formed was almost double the size of the crater produced by the inert bomb No 2. The damage caused was greater than the theoretical calculations indicated

Bomb No 5: A 50kg German bomb placed in a vertical position on the ground with its side in contact with a 3ft 3in thick outside wall. The bomb was detonated electrically.

Bomb No 6: A test to ascertain the resistance of the target to the maximum explosive effect of a larger bomb than the British 500lb bomb for which the roof was designed.

A German 500kg SC bomb was placed on its side on an undamaged part of the roof slab and detonated electrically. Although the concrete shattered the slab, it was held in place by the tension of the reinforcement.

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An image of a geothermal diagram
An early test result scan from the geophysical survey. The blue and dark blue areas show an empty space underneath the ground where the 'Sub Pen' was buried, confirming chambers inside the structure still exist© Courtesy New Forest National Park Authority
A black and white photo of an old bomb testing site in the countryside
The building was disused in 1946© Crown Copyright
A black and white photo of a series of bombs lying around during World War two
The RAF tested some of its largest aerial bombs at the site © Crown Copyright
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