‘An explosion in air does not transfer much energy into a solid, due to acoustic impedance.’ Everyone knew that – no-one more so than bouncing bomb mastermind Barnes Wallis, who, during the Second World War, conceived an idea designed to shake German industry to its foundations.
At the time, a number of factors allowed engineers to make vital installations virtually proof against aerial bombardment. Contemporary bombing under anti-aircraft fire was very inaccurate, but even in the event of a direct hit, many buildings were so well protected by yards of concrete shielding that they might survive even that.
Wallis, forever the lateral thinker, planned to attack such structures from the ground up, embedding a vast explosive under the site of a protected target. But how?
The idea was to drop a huge, heavy bomb with a solid armoured tip from 40,000ft so that it broke through the ground and buried itself 130ft underground near the target, where it would detonate. The explosion would create a shockwave comparable to a small earthquake. This would shatter concrete reinforcements and destroy nearby dams, tunnels, railways, and viaducts.
Wallis predicted that an underground cave would be created by the blast beneath the target, into which the structure would collapse; a process referred to as a ‘trapdoor effect’.
It was not until the success of his bouncing bomb later in the war that RAF Bomber Command decided that Wallis was a man to be listened to – however strange his ideas might have sounded. They provided him with the means to develop his designs. Though he was never to see his vast Earthquake Bomb actually made, Wallis did use the concept to create other explosive devices with great success.
The ‘Tallboy’ and the ‘Grand Slam’, although smaller than the original and never dropped above 25,000ft, were used effectively to disrupt German industry. They rendered the V2 factory inoperative, destroyed the V3 guns, were vital to the sinking of the Tirpitz, and caused considerable damage to the U-boats’ protective pens at St Nazaire.
Although Wallis’ vision of the giant Earthquake Bomb was never realised, and the necessity for such specific bombs was nullified with the development of nuclear weapons, these smaller versions were a success at the time. Today, the US Army has in its arsenal the Massive Ordnance Penetrator: a precision-guided bunker-buster designed to attack deeply buried targets without the use of nuclear weapons. Wallis would have been proud.