An idea begins
Sir Barnes Wallis worked for Vickers, designing new aircraft that would carry the war to Germany. At the start of the war he was attempting to design a replacement for the Wellington. The Warwick was giving him problems with the tail unit and also interfering with his thoughts on how he could bring a quicker conclusion to the war. He did not know much about bombs but was convinced that bigger bombs were the answer. Earthquake bombs would bring the industrial might of Germany to its knees. Unfortunately the present explosive used was useless, the maximum size of bombs was limited to 500lbs and there was no aircraft that could carry 1,000lb or bigger bombs.
Whilst reading about their construction in manuals kept in an Engineering Library he was sure he had picked the right answer when he read the engineers assessment of the effects of breaching the dams. It would not merely destroy the hydro-electric power and deprive foundries of essential water. It would also affect other war industries that needed water for their processes, deprive the surrounding population of water services, and breaches in the dams would send water flooding down the valleys disrupting infrastructure. The theory was fine but a 500lb bomb would hardly scratch the concrete and a bomb twenty times bigger would not damage them either.
He had read of concrete piles shattering when they were being piled into the River Thames. It was the ability of water to focus the shock waves that moved him into thinking of exploding a bomb in the water. He calculated that a ten-ton bomb with 7 tons of explosive in an aero-dynamically-designed case of special steel, dropped from 40,000 feet, would reach a speed of 1,440 feet per second, or 982 m.p.h. well over the speed of sound. At that rate it should penetrate an average soil to a depth of 135 feet. Barnes Wallis felt he was well on his way to finding the answer.
Wallis must have been extremely frustrated over the following months. No one wanted to hear about his big bomb theory let alone plough through the reams of backing calculations. However eventually a committee was set up of designers and scientists and a Doctor Glanville of the Road Research Laboratories at Harmondsworth suggested building a model dam and testing the theories with scaled down explosive charges. Over the following months when he could get away from Vickers, Wallis helped build a model dam one-fiftieth the size of the Moehne with tiny scaled down cubes of concrete. The model was about 30 feet long, 33 inches high and up to 2 feet thick and one side was flooded to simulate the lake.
The big problem was that when he actually did significant damage to the model he calculated that scaled up he would need 30,000lbs of the new explosive RDX. This meant with the weight of the necessary special steel to hold the explosive he would have a bomb of 70,000lbs, over 30 tons. The Victory bomber, still only on paper, would only be able to carry a maximum of 10 tons. He was not ready to give up. If he could explode a bomb up against the wall of the dam or maybe several bombs in the same place the damage would be significant but how could he guarantee the accuracy?
He remembered skipping stones over a lake whilst on holiday with the children. Using an old bath tub in his back yard he started experimenting with an elastic band and his children’s marbles. He found he could control the length of travel of the marble by adjusting the tension on the elastic, if he could control a bomb to stop up against the dam and then sink to a pressure-fused height he could ensure all the bombs exploded in the exact same place but he needed to know how large a bomb he needed. After working with Dr. Glanville on another model dam he found a very small amount of gelignite exploding against the wall of the dam shattered the model. When he scaled up the results on paper he found he would need only 6,000lbs of RDX to breach the Moehne Dam. Adding the weight of the bomb’s casing gave you 9,500lbs which was less than 5 tons, well within the specifications of the new Lancaster bomber.
It is amazing how fast government departments can react if an idea looks acceptable. Professor Patrick Blackett, who was head of an operational research branch listened and said, “We’ve been looking for this for two years.” He went and saw Sir Henry Tizard and told him of the idea and Sir Henry went down to see Barnes Wallis the very next day. He needed to see if Wallis’s idea would work in practise. Wallis had done his homework and said there was a huge ship-testing tank at Teddington where he could work out the exact logistics of the bomb. When asked how they could check the accuracy of the amount of explosive needed Wallis told him of an old disused dam in Radnorshire owned by the Birmingham Corporation. He worked out it should have a fifth of the resistance of the Moehne dam and armed with some RDX he blew a hole 15 feet across and 12 feet deep on the first attempt at Radnorshire.
The following months were spent at Teddington working out how to control the spin of the bomb, its best shape and size so that it would fit in a Lancaster and the fact it needed to be turned backwards just before it was released so a belt drive would be needed to spin the bomb. This had the added advantage that when it hit the dam it would keep turning against the wall of the dam as it slowly sank to the required depth. By the middle of 1942 he had a barrel shaped bomb weighing 5 tons that would skip across water, hit the dam surface and the residual back spin would keep it against the dam as it sunk down the face of it.
Wallis eventually got the go ahead to make 6 half size bombs that could be dropped by a Wellington. Mutt Summers, the test pilot for Vickers and long time friend of Wallis’s would fly the two-engine Wellington with Barnes Wallis as bomb aimer. When the bomb was dropped it hardly bounced at all and burst into pieces. The following day with a strengthened bomb casing they watched the bomb bounce for over half a mile and both Wallis and Summer were giving each other thumbs up all the way back home.
It was Mutt Summer who introduced Barnes Wallis to Air Marshal Sir Arthur Harris, chief of Bomber Command, a man who distrusted all inventors and was very difficult to convince. He watched the films and said he would not give Wallis a squadron of Lancaster’s based on a lot of theoretical work. Wallis said he only wanted one to prove it in trials first. For the next few weeks Wallis appeared to be getting nowhere until on the 26th February he was summoned to London and told, “Orders have been received that your dam’s project is to go ahead immediately with a view to an operation at all costs no later than May.”
PART TWO of this article will follow shortly!