bouncing bomb
by Taliesin's Muse Mon Apr 14 2003 at 9:00:22
The bouncing bomb (also named "Highball") was invented by Barnes Wallis during WWII, to destroy German dams by dropping a bomb at low altitude, and skipping it across the water of the dam like stones skip on a pond. The attacks using the bouncing bomb were immortalised in the Paul Brickhill book "The Dam Busters" (later a movie).
An engineer and aircraft designer, Wallis used his spare time to work on projects that he hoped would shorten the duration of the war. His field of expertise was in engineering and aircraft design, and he had, moreover, a considerable amount of knowledge about bombs - having designed bombers himself. The R.A.F. bomb stocks were old - many left over from 1919, and only 25 % of their weight was explosives - and fairly mediocre explosive at that. The heaviest bomb was only 500lb (about 225 kg), and aiming it was unpredictable. Great quantities of them were dropped in a method known as stick bombing - hoping that one would hit the target.
In addition, factories that produced weapons and other necessary war paraphernalia were scattered all over Germany. Bombing would damage the German war effort, but not drastically. Wallis started searching for different targets - and decided on dams. The German steel refining method required 8 tons of water to produce a ton of steel. To destroy the main German dams would set back weapons production dramatically.
As matters stood, no bomb was capable of destroying a dam. The chances of a direct hit were low - and the small bombs would cause only minor damage. Wallis looked for a way to amplify the shock waves of the explosion, and to contain them, so that the dam would take the full brunt (the concept is sort of explained in the movie Armageddon: "Imagine a firework on the palm of your hand. You set it off - what happens? You burn your hand. You close your fist around that same firework - and your wife's gonna be opening your ketchup bottles for the rest of your life"). A large bomb buried in water or earth near the dam would have an earthquake effect, and destroy the dam.
At first Wallis planned a 10 ton bomb to be dropped from a great height next to the dam, that would sink near the dam and explode. He designed the Victory bomber - a 50 ton bomber that would be capable of carrying such a bomb, and also designed some smaller bombs - 2 ton and 6 ton - for earlier production.
Wallis was unable to interest the military in his ideas for some time. When he finally did - he ran into difficulties with his design. Even using RDX - a newer, more powerful explosive, the level of accuracy required for a 10 ton bomb seemed impossible, and when more realistic levels of accuracy were tested, a 30 ton bomb was called for. Wallis began to look for ways to get a bomb to sink right next to a dam wall. Eventually, he was inspired by watching his children skipping stones on a pond. Wallis experimented with marbles and a catapult, and found that by varying the force applied he could bring a marble to a stop fairly close to a given point. He conceived the idea of a bomb that did the same thing, postulating that the bouncing motion of the bomb would allow it to skip over torpedo nets, and slow to a stop just before the dam wall, when it would sink.
Barnes Wallis then went back to the drawing board. He had been unable to garner any great interest for his "earthquake" bomb, and was chary of speaking of his new idea, being fully aware that it sounded like a crackpot theory. After much research, he sought approval for testing. The idea was approved of by a few officials, and he was given the green light to test his calculations on the amount of explosive needed - on a disused dam in Radnorshire. The results showed that a 5 ton bomb would do the job, provided it could be sunk next to the dam wall. The first tests in late 1942 with half-sized prototypes did not go according to plan. The shock of hitting the water deformed the bomb - ruining the bouncing motion. After strengthening the bomb casing and giving the bomb a backspin on launching - the small prototypes worked perfectly, coming to a gentle stop about half a mile from where they had first hit the water. Wallis continued to meet with setbacks. Though he had convinced several officials of the bomb's efficacy, military command is a convoluted web, and many times the project suffered setbacks due to red tape and obstruction by sceptical officials. However, early in 1943 he was given permission to carry out tests with a full sized bomb and a converted Lancaster bomber. 617 squadron was formed, commanded by Guy Gibson (D.F.C, D.S.O. and bar), to be trained in night time low altitude flying. Wallis had specified a speed of about 240mph, holding an altitude of 150 feet, in order for the bomb to fall properly. If the bomb bounced over the dam wall instead of sinking near it, the resulting explosion would be extremely likely to blow the aircraft out of the sky. Eventually, the altitude was reduced to 60 feet (about 20 metres - a terrifyingly low altitude) and the bomb sank in the tests at precisely the spot targeted.
The product:
The bouncing bomb measured 60 inches long and 50 inches in diameter. It was a barrel shape (the original sphere did not fit under the Lancaster bomber) that was launched from v-shaped arms under the plane. The bomb bays of the Lancaster had been removed, and a hydraulic motor and belt drive generated a 500rpm backspin on the bomb. The backspin kept the bomb skipping - rather than having it dive into the water from the forward spin generated by the first bounce.
The bomb contained 3 hydrostatic pistols, to measure the pressure of the water as the bomb sank. The bomb would detonate at 30 feet depth, and a backup 90 second time fuse ensured that the bomb would still detonate even if the hydrostatic mechanism failed. The bomb weighed 9,250lb - 6000lb of which was a combination of TNT and RDX explosives.
On May 16, 1943, the "dam buster" raid was carried out. The bouncing bomb worked perfectly. Three formations from 617 squadron flew out - the first to attack the Moehne and Eder dams, the second to attack the Sorpe dam, and the third as a mobile reserve unit. The Moehne dam was destroyed with four highball bombs (a fifth was launched but shot over the dam wall, the explosion engulfing the plane), and the Eder destroyed with two (and again, another fatal overshot). There were successful drops at the Sorpe, but the dam wall was not destroyed. Of the 19 aircraft that flew the mission, nine returned. Wing Commander Guy Gibson received the Victoria Cross, and 33 of the aircrew were decorated. 330 million tons of water were flooding the mines, factories, aerodromes, powerstations - and villages - of the Ruhr valley in Germany. The disruption to industry and military action is hard to gauge, but there was widespread flooding and disruption of rail, road and canal communications, and of the supply of electricity and water. German troops were deployed to the Ruhr, removing them from other vital areas. The total number drowned is quoted at 1,294, and the bouncing bombs were not used again.
"The Dam Busters" by Paul Brickhill, Evans Bros Ltd, 1951
   
This writeup has been cooled by: Professor Pi, Tem42X
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