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This episode of Real Engineering is brought to you by Brilliant, a problem solving website
that teaches you to think like an engineer.
If we were to define WW2 in just one technology, the likely winner would be aerial bombing.
World War 1 revolved around stagnant and debilitating trench warfare, that both sides sought to
avoid in future.
Tanks and planes arose as a way of breaking enemy lines quickly and inflict damage.
The rate of technological progress for delivering larger and more accurate bombs during world
war 2 was astronomical, but early in the war the technology was still in its infancy.
The Germans relied heavily on the Stuka dive bomber.
A short range bomber whos siren became a harbinger of death on the battlefield.
It dived towards its target, planting it firmly in its crosshairs, imparting its bomb with
the velocity it need to fly straight to the target, before releasing and pulling up hard
to avoid a collision with the ground.
This procedure was so taxing on its pilot that the Germans developed an automatic dive-flap
that would deploy even if the pilot had knock themselves unconscious with g-force.
These tactics arose because bombing aiming technology was so primitive, bomb sights were
rudimentary and required skilled operators.
Having to factor not only the speed and altitude of the aircraft, but the terminal velocity
of the bomb and how it would be affected by wind as it fell.
Bombing from high altitude, where the bombers would be relatively safe from Flak, gave little
precision to target specific buildings.
This combined with poor navigation equipment resulted in both sides devolving into carpet
bombing, causing massive loss of life to civilian life, which did little to help either side
win a war.
We saw in a previous episode how much effort Nazi cities put into anti-aircraft defences,
and similar efforts were made in Britain.
These tactics did not come cheap, losses were high for both sides..
Barnes Wallis, an Aeronautical Engineer at Vickers, saw the futility in these tactics
and set his focus on developing new technologies to aid British bombers in destroying strategic
German positions.
This was nothing new.
Factories, oil storage and transportation infrastructure were always primary targets,
but Barnes wanted to create a weapon capable of destroying a target others deemed invulnerable.
Dams posed a tantalizing target.
They supply hydroelectricity, provided water for industry and the German population, and
the resulting deluge of water from the massive reservoirs would cause damage much greater
than any bomb the Brit’s had at their disposal.
The Germans were not ignorant to the allure the dams as a bombing target.
Attacks on dams had happened earlier in the war, like the attack on the massive Italian
Tirso dam in Sardinia, which held back Europe’s largest man-made lake and provided the Italian
island with a third of its electricity.
They attempted the raid in broad daylight with 8 Swordfish floatplanes.
3 simply failed to find the target due to terrible weather, and the rest were welcomed
with anti-aircraft fire, taking one of the planes down.
The remaining 4 continued to the target and dropped torpedoes which travelled underwater
to their target before exploding, but the dam remained standing.
The bombs were simply not powerful enough to blast through the heavy concrete of the
To make matters worse, all dams across Europe would be protected by anti-torpedo netting
from this point on.
So a new method to deliver an enormous bomb capable of taking down a structure this strong
was needed.
Wallis spent most of his time devising devices to take on challenges like this, and took
several things into consideration when designing his bombs.
Explosive pressures decay extremely quickly, and thus to ensure damage to the structure
it must be as close as possible, pressure waves propagate through denser mediums far
more efficiently, and thus explosions underground or in water will be more powerful.
And finally, doubling the size of the bomb does not result in twice the blast radius,
to increase the blast radius drastically would require a drastically larger bomb.
His design ethos from here was simply.
Design the biggest bomb his planes could carry, and have them detonate underground or in water
to maximise their effect even further.
He presented his ideas in a 1941 paper “A Note on a Method of Attacking the Axis Powers”
with the primary focus on a 10 tonne earth penetrating bomb, that would be dropped from
40,000 feet, this was the most powerful non-nuclear bomb ever used until just last year, and 42
were dropped in the final year of the war that helped cut German supplies to the front
line, by destroying viaducts and railways.
But Wallis is remembered for a different bomb.
The British government hired the Road Research Laboratory, a civil engineering firm, to begin
experiments to find the smallest charge needed to destroy the Mohne Dam.
They constructed several scale model dams, and used abandoned dams in Wales to find their
They found that even a 10 tonne bomb exploding 50 feet from the dam would not destroy it,
but a 2 tonne bomb could do the job if it was placed directly next to the face of the
With torpedo netting installed, this job required precision that had not been seen before, and
the method that was devised would break all convention.
Barnes decided the best course of action was to create a skipping bomb, that would bounce
over the protective netting before sinking next to the dam and exploding.
He concluded that the mines would have to impact at less than 7 degrees in order to
skipp, and all subsequent bounces would also have to be below 7 degrees to ensure the bomb
continued until momentum was lost.
The bomb would be given a backspin prior to release in order to take advantage of the
Magnus effect, which is lift created by a spinning body.
Spinning the bomb provided it stability, like a bicycle wheel in motion.
Helping the bomb remain on a straight trajectory, but the lift the spinning provided was far
more useful.
By adding lift the bomb’s trajectory gained more horizontal motion, and it’s angle of
impact was reduced.
Both of which aid skipping, and allowed the bomber to release the bomb sooner, giving
them additional time to escape the imminent explosion.
Once submerged the remaining spin would then help push the bomb forward ensuring it stayed
in close contact to the dam wall.
This wholly unconventional bomb posed some design challenges.
Any spinning object needs to be precisely balanced to prevent vibrations that could
potential break it, or interfere with it’s operation.
To aid this, Barnes early spherical designs were scrapped in favour of a drum which could
be more easily manufactured and balanced, while also aiding with it’s release mechanism.
The bombs were fitting to Avro Lancasters, which were modified to accommodate the bomb
. The bomb doors were removed to fit bomb, which would protrude below the plane for the
duration of the flight.
The lower ventral guns were removed to reduce drag, as the mission would be flown so low
to the ground that they would provide no protection against fighters.
Two v-shaped mounting arms were then attached with free-spinning disc mounts which would
mate with the support rings on either side of the bomb.
An off the shelf motor, typically used to power hydraulic pumps on submarines was used,
and connected to the bomb with a pulley.
Finally, to release the bomb Barnes needed some way of unmating bomb from it’s spinning
This was done rather ingeniously.
These mounting arms were stabilised with a tensioned wire, which kept them firmly mated
with the bomb.
When the bomb needed to be released, the tension was released with a solenoid actuated grip.
Compressed springs would then force the arms to swing outwards by just a couple of degrees,
enough to release the bomb
The bomb was now ready, but little time was afforded to the crew that would man the planes
that would carry them.
A new special squadron was created specifically for this mission, formed by some of the most
experienced pilots the RAF had to offer.
This experience would be needed, as the entire mission would be flown at extremely low altitude
at night.
Navigators had to learn to navigate with limited information, often little more than the bomb
aimers calling out landmarks they passed over.
To increase the time they had to train, their Lancasters were fitted with blue plastic screens
to the windows to limit visibility and light during the day.
After many test drops the crew were finally informed of their target on the morning of
the attack on May 16th.
That night they would take off from RAF Scampton in 3 waves with a total of 19 aircraft.
Little would go smoothly from here.
The first of the planes was lost just an hour into the mission, when it strayed off course
over the heavily defended Texal Island off the Northern coast of the Netherlands.
Two planes collided with power lines and cables as they flew low over the dutch and german
Another plane flew so low as it crossed the North Sea, that the low slung bomb collided
with a wave, dislodging it and forcing it’s crew to return to base, followed shortly after
by another plane badly damaged by Flak.
At this point the entire first wave of planes had failed their mission, but others were
finally reaching their target.
Gibson, the commander of the squadron, was the first to arrive flying at 370 km/h just
60 ft from the water, he successfully dropped his bomb which bounced three times before
sinking and exploding, sending a gigantic spout of water above the dam, but it had sunk
too short of the dam.
On the following run a bomb bounced over the dam and destroyed the powerhouse at its base,
while the Lancaster that carried it crashed into flames after being struck by flak.
Gibson at this point circled back around to act as a decoy, for Henry Young whos bomb
veered off towards the banks of the reservoir.
On the fourth try the squadron finally got a direct hit, but another blow was needed
to collapse the dam, which came shortly after as Gibson and Micky Martin flew decoy runs
alongside Maltby who scored a direct hit on the already crumbling dam, sending 330 million
tonnes of water into the valleys below.
With their first target down, the 1st wave continued on to Eder dam with 3 bombs left,
which was all they needed.
After two unsuccessful attempts, where one bomb damaged the plane that was dropping it,
Knight’s Lancaster came in at the perfect speed and altitude, releasing his bomb before
quickly pulling hard to avoid the 300 ft hill directly behind the dam.
The first wave were now out of bombs and made their journey home, but this leg was just
as dangerous, as the already damaged plane was shot down soon after.
2 more lancasters would also be brought down by flak on their return leg
The third wave lost two planes before reaching their newly assigned target.
One strayed over the city of Hamm and was gunned down by anti-aircraft guns, another
was lost over the Netherlands.
What remained mounted an unsuccessful attack on the Sorpe dam, before returning to base.
In all the British lost 8 Lancasters in the raid, killing 53 men, while another 3 who
managed to survive their crashes were taken prisoner.
But the damage inflicted on the Germans was far greater.
The resulting floods wreaked havoc on the Ruhr valley, every bridge downstream for 45
kilometres was destroyed.
10 factories were destroyed and a further 100 were damaged.
Mines were flooded, and an estimated 400,000 tonnes of coal production was lost.
Acres of farmland were wiped out, and over 1500 people died in the resulting floods.
All this damage with just 19 aircraft, this was precision that had not been seen before.
However, some have questioned whether the raids were worth this loss in life.
Many of the people killed in the floods were prisoners of war in forced labour, and others
are quick to dismiss this raid as a failure, because the Germans recovered so quickly.
Taking just 5 months to repair the dams, in time to ensure the reservoirs would fill for
the following summer.
But these people seem to ignore the immense amount of resources that had to be diverted
to repair the dams.
They were repaired quickly precisely because they were so vital to the German war effort,
that it was worth shifting thousands of works and materials away from the front lines.
D-Day, which would come just a year after this raid, could have gone very differently
if those resources had instead gone on to fortify the beaches of France even further.
These 19 bombers, pound for pound, did more damage to the German war effort than any other
British air raid thanks to the precision they had been engineered to achieve, and precision
would become the focus of many of the wars greatest engineers once the war had ended,
after all the Moon was much further away than any previous target.
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