Archaeologists are investigating a concrete structure at the Ashley Walk Bombing Range in the New Forest in the south of England. On 13 March 1945 it was used for a test drop of the 22,000 pound Grand Slam bomb, the largest bomb dropped until the first atom bomb.
The survey is using ground penetrating radar, magnetometry, electrical resistivity and electrical resistivity tomography to study the damage done to the large concrete target building. The bomb was dropped by a Lancaster bomber from 16,000 feet and hit the ground at 700 mph. It achieved its objective of creating a large but localised earthquake, leaving a crater that was 70 feet deep with a diameter of 130 feet. It has subsequently been filled in.
The archaeologists want to find out how much damage was caused by the bomb.. The Independent newspaper reports that:
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.
The Grand Slam had been conceived by Sir Barnes Wallis five years earlier as a deep penetration bomb. It was first used against the Schildesche railway viaduct near Bielefeld Railway Viaduct on 14 March 1945, the day after the only test drop. The viaduct, which was a vital communications link for the Ruhr and had survived several previous bombing raids, was brought down.
Over 40 Grand Slams were dropped in nine raids, with other targets including railway bridges at Arnsberg, Arbergen and Neinburg, submarine pens at Bremen and gun emplacements on the island of Helgoland.
The Lancasters that dropped Grand Slams had to be stripped of their gun turrets and the armour plating behind the pilot’s seat in order to increase their bomb capacity from its normal 14,000 pounds. Their bomb bay doors were also removed because of the size of the bomb.
Grand Slams were also made in the USA, which but the USAF had not used any by the time that it dropped atom bombs on Hiroshima and Nagasaki.