As Britain and France declared war on Germany and fighting began across Europe in September 1939, Barnes Wallis asked himself what he, as an engineer and aircraft designer, could do to shorten the war. Many of Wallis’ ideas were often regarded as impossible and far-fetched, yet his tenacity saw them through development, and the quality of his engineering was demonstrated time and again as his special weapons performed exactly as he had predicted.
Over the next six years, Barnes Wallis worked on a variety of aircraft and munitions, and while the magnitude of his contribution is impossible to measure in isolation, it is widely accepted that his ideas and innovations shortened the war considerably.
Wallis spent some time investigating how the energy sources of the axis powers (Germany and Italy) may be reduced or eliminated. Specialist publications provided him with all the necessary background information on the German dams and he formed the opinion that knocking out the water reserves of the Ruhr would curtail steel production severely.
“I thought of what would be an engineer’s way of stopping the war and that would be to cut off the power supply to their great armament factories in the Ruhr, which involved bombing and destroying the dams because you know it takes 150 tons of water to make 1 ton of steel and if we robbed them of all their water supply they couldn’t produce steel and the war would have come to an end…”
An ‘Air Attack on Dams Committee’ was formed in 1941 under the chairmanship Dr. Pye. The committee decided that the primary target should be the Möhne Dam which enclosed the Möhne and Hedve rivers. The dam was 130 feet high and 112 feet thick at its base. Even the top was 25 feet thick making it a formidable target to destroy.
The first idea Wallis had was to attack the dam with a series of very large bombs in a conventional manner. He quickly dropped this idea as the accuracy required for such an aerial attack was simply beyond the capacity for a bombardier at several thousand feet. A bomb would need to land within 50 feet of the dam’s wall for it to be effective and in July 1941, the Air Attack on Dams Committee concluded that an attack on the Möhne Dam is impracticable with existing weapons.
Upkeep & Highball – The Bouncing Bomb
Undeterred, Wallis was keen on the idea of getting an explosive charge as near to the wall of the dam as was possible. Wallis believed that if this could be done on the lakeside of the dam, the vast pressure applied to that side of the damaged wall would be enough to destroy the dam itself. A torpedo type bomb was out of the question as the Germans had already predicted this type of attack and had deployed anti-torpedo nets to protected the dam. Wallis came up with an idea he called “childishly simple”.
What is a Bouncing Bomb?
A bouncing bomb is a bomb designed to bounce to a target across water in a calculated manner to avoid obstacles such as torpedo nets, and to allow both the bomb’s speed on arrival at the target and the timing of its detonation to be pre-determined, in a similar fashion to a regular naval depth charge.
Wallis obtained the facilities of the National Physical Laboratory to test out his theories in more detail, having carried out initial experiments in his back garden using his daughter’s marbles as projectiles fired from a homemade slingshot across tin baths of water. Over time Wallis experimented with projectiles made of wood, aluminium, steel and lead with a view to obtaining the optimum weight, size, design speed and bounce distance on the balls to maximise the skip technique.
In August 1942 Wallis was able to convince the Ministry of Aircraft Production that the concept of skipping a bomb onto the dam face was feasible. The spinning bomb skipped better than an un-spinning weapon and the backspin that was imparted had the secondary benefit that when the projectile hit the dam face, it ricocheted away but the remaining back spin drew the bomb back onto the dam face where it sank and would be exploded by a hydrostatic pistol of the same type used on depth charges. Tests were approved.
In December 1942 a Wellington Bomber, flown by Captain Mutt Summers, descended over Chesil Beach in Dorset and having lined up carefully with cameras on the beach made its run and dropped the bomb. Unfortunately the bomb disintegrated when it struck the water. Tests continued with bombs being dropped and Wallis rowing out in a boat at low tide to inspect the casings. With each test, modifications were carried out to the casings and trials continued in January 1943. Finally on 5th February Wallis had proved possible to skip the bomb for over 1300 yards and for it to generally remain intact at the end.
On January 28th Wallis showed the films of the Chesil Beach tests to a gathering of high ranking staff from the Air Ministry and Ministry of Aircraft Production. The Royal Navy expressed considerable interest with a view to using the weapon against the German battleship Tirpitz and in fact by the end of January an order for 250 weapons was placed on behalf of the Royal Navy who were impressed with the potential of the weapon.
Wallis however, still felt that the best use for his weapons was against the German dams and proposed therefore that the dam’s weapon, now codenamed “Upkeep” and the Royal Navy anti-ship weapon, now codenamed “Highball” be developed together. He was concerned that in the event the Royal Navy used the weapon against ships the technology would be made available to Germans and the element of surprise lost.
The first drop of the Upkeep prototype from a modified Lancaster was made in April 1943 off the Kent coast near Reculver. Unlike the final cylindrical operational weapon, the prototype remained spherical – the shape preferred by Barnes Wallis – and comprised a steel cylinder faired by wood into a spherical shape. It was unsuccessful and the wood broke away. A second drop later the same day produced the same result, but the cylindrical main part performed as intended. It was decided after a third unsuccessful attempt on April 22nd to dispense altogether with the wooden covering. Only three weeks before the actual attack, the bomb worked satisfactorily for the first time on April 29th.
Wallis had also been working on a smaller version codenamed “Baseball” which he was planning to fire at warships from motor torpedo boats. The whole family of bombs were given the codename “Golfmine”.
The Legend of the Dambusters
At the end of February 1943, a unique decision was taken to form a crack new squadron comprising some of the most experienced crews within No 5 Group – Bomber Command’s most seasoned Lancaster Group. Its commander was Wing Commander Guy Gibson, already a veteran of 174 sorties. The new squadron, soon to be designated No. 617, would be based at Scampton in Lincolnshire. Gibson would personally select his own crews, including quite a number from his old squadron, No. 106, to fly a top secret operation of a very special nature.
By 16 May, the date chosen for Operation Chastise, Gibson and his crews had spent 2,500 hours in training flying their specially modified Lancasters cross-country navigating by moonlight at low level. They practised the entirely new technique of releasing a mine from an aircraft flying at exactly 60 feet and at 232 mph over the Derwent reservoir in Derbyshire. The back-spinning cylindrical weapon was to skip over the water, bounce over nets and other defences, strike the dam, sink and detonate at 30 feet.
The correct release distance of 400 – 450 yards from the target was judged with a simple triangular sight using the known distance between the ornamental towers of the dams as a base. Two spotlights under the bellies of the Lancasters focused intersecting spots on the water surface to indicate the correct height.
Wing Commander Gibson made the first attack on the Mohne Dam releasing his mine at 28 minutes past midnight. Half an hour later, after the fifth Lancaster had attacked, he radioed NIGGER, signalling that the dam had been breached.
Gibson led the rest of his force to the Eder Dam directing them one by one into the attack. The same meticulous procedure was followed and the same extraordinary courage displayed. The final attempt by Pilot Officer Knight deeply breached the dam. The water spewed out, looking, as Gibson later wrote, like “stirred porridge in the moonlight”.
Both the Mohne and Eder masonry dams were breached. And the damage to the Sorpe earth dam with the one remaining weapon was such that the Germans drained off half the contents of the lake to ensure safety.
Of the 19 aircraft of 617 Squadron that took off that May evening in 1943 only 11 returned. But Albert Speer, Reich Minister of Armaments, said, “We were in great danger. If the English had systematically destroyed all the dams in the region, our steel industry would have collapsed”.
Gibson was awarded the Victoria Cross. Thirty-two other aircrew received DS0s, DFCs and DFMs.
Tall Boy – The Earthquake Bomb
“After the dams had been burst, Sir Wilfred Freeman, the Chief Executive at the Ministry of Aircraft Production, asked me if I remembered my mad idea of a 10-ton bomb which I had put up in 1939. I said ‘Yes, indeed, Sir Wilfred, I do’. ‘Well’, he said, ‘how soon could you let me have one?’ I said ‘June, July August, September, October, five months if I have all the labour available in Sheffield’”
Following the success of the Dambusters Raid, under the initiative of Sir Wilfred Freeman at the Ministry of Aircraft Production, Wallis returned to his earthquake bomb design. Initially, Wallis wanted a ’10 ton’ bomb (22,000lb), which would, ideally, have been released from an aircraft flying at 40,000 ft. Yet, since an aircraft capable of the task failed to exist at the time, a 12,000lb DP bomb (for ‘deep penetration’) was authorised; codenamed ‘Tallboy’.
Wallis revised his design, scaling the weapon down to be 21 feet in length and 38 inches at its maximum diameter. Its hardened steel case had a thickness of more than 4 inches in the nose. The bomb carried a charge of 5200lbs of Torpex explosive and detonation could be delayed up to sixty minutes. Released from the optimum height of 18,000 feet the bomb took 37 seconds to reach the ground, impacting with a speed of 750 miles per hour.
This destructive power was used to create a void deep under the earth after the body of the bomb, its nose made from tough forged steel, had punched its way underground. As this void collapsed, it left a large crater into which structures such as bridges and rail tunnels collapsed. Not only that, but foundations were shaken and weakened by the ‘ground waves’ caused by the explosion which could be up to 150 yards away and still be effective. Even if total destruction did not occur, the amount of damage inflicted would often be enough such as to make the structure uneconomic to repair.
The only RAF aircraft capable of carrying the Tallboy was the Avro Lancaster, rapidly becoming RAF Bomber Command’s standard heavy bomber. The Lancaster’s bomb bay doors had to be modified to accommodate the Tallboy, and it was decided that only a few squadrons (including 9 and 617 Squadrons) would be given the training and special SABS MkllA bomb sight needed to operate with the weapon. After a period of work-up these squadrons began attacking strategic targets such as the Samur Railway Tunnel in France, blocking it completely and preventing vital German reinforcements from reaching the D-Day beaches from the South of the country. An even more impressive feat was the sinking of the ‘Tirpitz’, a German battleship which was moored in Norwegian waters following damage in an earlier bombing raid, by Lancasters operating at their maximum radius of action from the Scottish airbase at Lossiemouth. On 12th November, 1944, Tallboys dropped by both Nos 9 and 617 Squadrons smothered the ‘Tirpitz’ and three direct hits were obtained; the battleship turned turtle.
Grand Slam – Ten Ton Tess
Following the initial operational successes, in July, 1944 Barnes Wallis was given the green light by the Ministry of Aircraft Production for his monster ’10 tonner’, the ‘Grand Slam’. The Vickers Don Valley facility in Sheffield was one of the very few forges which could handle the production of such a massive weapon. The steel casing took two days to cool down after being cast, before the difficult task of machining the body could begin. When ready, the bomb casing was filled with molten Torpex explosive. Amazingly, this took one whole month to set and cool. Consequently, because production of the bomb was so slow and expensive, aircrews were instructed to bring their weapon back to base if they were unable to drop them on target.
On top of the 9,200lb of cooled Torpex, a one inch layer of TNT was poured, (the explosion of which would initiate the Torpex), followed by 4 inches of a wood-meal and wax mixture which was then sealed with a half-inch plywood washer with three holes drilled through it to take the triple No. 58 fuse pistols. Finally, a heavy steel plate was bolted over the end of the bomb casing, then the special No 78 Mk1 tail with its four fins (offset at 5 degrees to induce a right-handed spin of over 300rpm and increase accuracy) was bolted on. Released from the optimum height of 18,000 feet the bomb took 37 seconds to reach the ground, impacting with a near-supersonic speed of 750 miles per hour.
To carry the enormous Grand Slam, even more changes had to be made to the Avro Lancaster bomber. The bomb bay doors were completely removed, as were both the mid-upper and the front turret, then a lightweight aerodynamic fairing was fitted in its place. Some of the standard armour plate on the aircraft was taken out, and higher powered Rolls-Royce Merlin 25 engines fitted. The resulting aircraft were designated the Avro Lancaster B.Mk I (Special).
The first wartime use of the Grand Slam bomb came on 14 March 1945 against the Bielefeld Viaduct in Germany. This vital rail link was attacked by 617 Squadron, 28 aircraft of which were carrying Tallboys and one a Grand Slam. The 22,000 pounder landed within 80 yards of the target and 11 seconds later a huge crater was created, which fatally weakened the structure; nearby Tallboy misses finished the work, and two spans of this vital transportation link collapsed. Raids on railway bridges, viaducts and submarine pens across Germany continued throughout March, 1945, with devastating results.
By the end of the war, no less than 854 Tallboys and 41 Grand Slams had been delivered, many with deadly accuracy.