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Bombing Hitler's Dams

Experts recreate the bold feat of “dambuster” pilots who used bouncing bombs to destroy two key German dams in WWII. Airing January 11, 2012 at 9 pm on PBS Aired January 11, 2012 on PBS

Program Description

In 1943 a squadron of Lancaster bombers staged one of the most audacious raids in military history: destroying two gigantic dams in Germany's industrial heartland and cutting the water supply to arms factories. Their secret weapon? A revolutionary bouncing bomb invented by British engineer Barnes Wallis. Wallis and the pilots of 617 Squadron—a lively mix of Britons, Australians, Americans, and Canadians—were hailed as heroes who dealt a mighty blow to the German war machine. Now, NOVA recreates the extreme engineering challenges faced by Wallis and the pilots. A crack team of experts, including dam engineers, explosives specialists, mechanics, and aircrew, steps into the shoes of the "dambusters" and attempts to overcome each of the obstacles the original team faced. They must adapt a vintage World War II DC-4 to carry a bomb the size of an oil drum, train to drop it from a dangerously low altitude, and get it to bounce over obstacles and onto the target, a scale model of the German dam struck by the original dambusters. Can they succeed in destroying the dam and unraveling the mysteries of the one-of-a-kind bouncing bomb?

Transcript

BOMBING HITLER'S DAMS

PBS Airdate: January 11, 2012

NARRATOR:It's the second year of World War II. Hitler's bombs are raining down on London. The British desperately need to find a way to strike back. In a nondescript drawing office, an audacious plan is taking shape. A brilliant aircraft designer, named Barnes Wallis, has come up with an idea that will cripple German industry in one daring raid.

After two years of planning and experimentation, a squadron of 19 Lancaster bombers heads for the industrial heartland of Germany. Each aircraft is armed with Wallis's secret weapon: a bomb that skips across water and destroys the strategically vital dams that supply power to the Nazi war machine.

HUGH HUNT (Lead Engineer): These massive dams were considered indestructible, so the idea that you could actually blow them up with a single bomb, at low altitude, spinning, bouncing on a lake and destroying the dam, I mean, it's just, it's just a fairy tale.

NARRATOR:Was Wallis's bomb one of the true marvels of military engineering, or was it a desperate gamble that paid off?

Now, an elite team of modern-day adventurers is trying to find out. They will build a massive replica of a German dam and attempt to re-engineer the bouncing bomb.

RICK DONNELLY (Dam Designer): I would have a lot of sleepless nights, if I promised to try and blow this up.

HUGH HUNT:Fire!

NARRATOR:With no blueprints of the weapon left behind, engineer Hugh Hunt will have to design it from scratch.

TOD TODESCHINI (Launcher Designer):Fire!

HUGH HUNT:Every step of the way has been, "Gee, how do we make this work?"

NARRATOR:It will take a dangerous combination of untested science and daredevil flying for the modern-day team to emulate the dam busters of World War II.

ARNIE SCHREDER (Buffalo Airways): It was a pretty phenomenal stunt they pulled off there, and dangerous, too, because they lost 53 people in that raid.

NARRATOR: And the margins of error are just as unforgiving today.

CHUCK ADAMS (Buffalo Airways): If there's a problem on this next drop, like this, the whole thing's going to wind up being cancelled.

NARRATOR:Can history be repeated? Bombing Hitler's Dams, right now, on NOVA.

January, 1942: The Allies are on the defensive; Europe is an impenetrable Nazi fortress; the Japanese are sweeping all before them in the Pacific and have wiped out most of the U.S. Naval fleet at Pearl Harbor, drawing America into the war. And in the Soviet Union, Hitler's tanks have charged across the steppes, pushing the Red Army back towards Moscow.

Fifty-three-year-old Barnes Wallis, one of Britain's most talented aircraft designers, resolves to find an engineer's way of stopping the war. Working for a huge armaments firm, Wallis's pioneering work on airships has already cemented his reputation: in 1930, his mighty R100 airship crosses the Atlantic at speeds that reach 80 miles per hour.

Wallis turns his hand to designing aircraft and comes up with one of the most successful planes of the Second World War, the Wellington Bomber.

The Wellington is soon rolling off the production line at an unprecedented rate of 45 per week. Over 11,000 are produced, a number unsurpassed, even today, by other British multi-engined aircraft.

Despite his heavy workload, Wallis still finds time to develop a bold plan. He knows it takes 150 tons of water to make one ton of steel. If he can find a way to turn off the tap, the Nazi war machine will grind to a halt.

Germany's heavy industry, concentrated around the coalfields of the Ruhr Valley, is fed by a small cluster of huge dams. If British bombers manage to breach these dams, it will deprive Germany's most important steelworks and hydroelectric power stations of water, and flood the coalmines and factories, downstream.

The military planners reject the idea. They don't have a weapon capable of destroying the dams. But Wallis believes the key to turning the tide of the war lies here.

Wallis knows that it is difficult for bombers to hit the thin crest of a dam from the air.

The British consider using a big torpedo instead, but the Germans have strung up steel nets to protect their dams.

Wallis's solution is the stuff of legend: he will design a spinning drum of explosives that will bounce over the nets and into the dam. To deliver the weapon, a squadron of Lancaster bombers must fly, by moonlight, deep into enemy territory.

Over the target, they must release the bomb from a set height, set speed and set distance from the dam, while under intense fire.

The story of Barnes Wallis and the bouncing bomb has entered wartime mythology. But exactly how Wallis figured out his ingenious weapon is lost to history—until now.

At Trinity College, Cambridge, one man is determined to solve this 70-year-old mystery by repeating Wallis's feat of military engineering.

And here is the modern-day Barnes Wallis: Dr. Hugh Hunt.

HUGH HUNT: Hello? So, this is ground control to nerve center.

NARRATOR: Hugh is a senior lecturer in the Department of Engineering and a fellow of the college.

HUGH HUNT: Okay. So we're clear now, I think, to move the bombs out.

NARRATOR: He's a world authority on the physics of spinning objects, and he's fascinated by the mysterious forces that affect the way they fly through the air.

HUGH HUNT: Five, four, three, two, one, drop.

I'd heard of the Barnes Wallis bouncing bomb story. And just like everybody else, I thought, "Oh, that looks simple."

NARRATOR: No country on Earth allows live bombs to be dropped from a civilian aircraft over their territory. But in a remote part of northwest Canada, authorities agree to allow heavy objects of an equivalent weight and size to be dropped from the air.

This is the laboratory for the colossal experiment.

Canadian engineers will build a concrete dam next to an enormous lake. The dam's design is unusual. Rather than damming up a river, they'll dig a trench right up to the lake, build their dam in it and then let the water in. If the dam is successfully breached, the flood will be safely contained in the trench and will not tear up the landscape.

Contractor Jim Bellavance has just 25 days to build the 30-feet-high, 4,000-ton dam.

JIM BELLAVANCE (Dam Contractor): It's a big structure we're putting up here. When it's finished, it's going to be pretty impressive. I can hardly wait for the day that we open that ditch up and the water flows up behind it. Then we're really going to see what we've got.

NARRATOR: Back in Britain, Hugh begins his quest by visiting the Barnes Wallis Archive.

HUGH HUNT: The cylindrical form might be more effective than the spherical, and it certainly looks much more practical from the manufacturing point of view.

June, 1942.

NARRATOR: He's looking for details of Barnes Wallis's original experiments to help him build his bomb.

HUGH HUNT: What I wanted to see was calculations. I wanted to see his notes. I wanted to see the things that didn't work. I wanted to see the, the stuff that really went on in his mind. But they weren't in the archive, so I really have to do all this stuff again, from scratch.

NARRATOR: Many of those vital papers were lost in a flood in the 1960s, but Hugh finds a tantalizing photograph.

HUGH HUNT: Well, this picture, from April, 1942, shows the initial experiment in his back garden. Barnes Wallis with his kids, what looks like a catapult, firing over a laundry pail full of water. Looks great.

NARRATOR: With the help of his children, Wallis fires marbles from a homemade catapult to try to find the critical angle a heavy object must strike water to make it skip. This is his first attempt to test his idea of skipping a bomb across water and over anti-torpedo nets.

Unfortunately, the results of the marble tests are missing from the record, so Hugh decides to restage the experiment on the banks of the River Cam, at Trinity College.

With little more than the grainy photograph as a reference, he drafts his children as assistants and a pair of trusty students.

HUGH HUNT: Both hands, Johnny.

NARRATOR: Instead of a catapult, Hugh uses a device used in cricket practice to fire balls at high speed.

HUGH HUNT: Barnes Wallis did tests on little marbles to start with. Well, we've got this bowling machine, so this is our starting point. It's a bit bigger than Barnes Wallis's, but that's fine. It's still the same principle.

All right here we go. Three, two, one.

So, that didn't bounce.

NARRATOR: Hugh starts to vary the speed of the ball and the angle at which it strikes the water.

HUGH HUNT: So, one thing I can try and do is get the angle shallower, by moving this further back.

Okay, let's increase the speed a bit, as well. Okay, are we ready?

Three, two, one, fire.

Well, that was a nice bounce.

Okay, next one. Fire.

Oh.

We can measure the angle that it goes into the water and the angle it comes out, the speed it goes in and the speed it comes out. And these kinds of things are important to understanding the physics of what's going on.

NARRATOR: He finds that for a ball to bounce, it needs to be traveling at 30 miles per hour; it must strike the water at an angle of no more than seven degrees.

In June, 1942, Barnes Wallis scales up his experiment. Eventually, he'll need to skip a heavy bomb over the submarine nets and into the dam. He builds a large catapult to test fire a whole range of spheres, of varying weights.

He manages to get even heavy lead balls to skip, by using a 400-year-old naval technique he's read about, called "skip shot." Gunners who wanted to pierce the hull of a ship deliberately skipped their cast iron cannon balls over the surface of the water.

COLIN HERRIETT (Gunnery Expert): Ready?

NARRATOR: Gunnery expert Colin Herriett demonstrates how it was done.

COLIN HERRIETT: There's nothing better than puncturing the hull below the water line, and that's where this skip shot idea came into its own.

NARRATOR: The gunners wouldn't fire until the enemy ship heeled away from them, exposing the hull below the waterline. For the technique to work, the cannon had to be fired from close to the surface of the water.

COLIN HERRIETT: He would shoot at point-blank range, which means the barrel is flat—not close up, which is the modern definition of this—so that the ball would come in at a very, very fine angle and then kiss off the surface of the water, just, just like children flicking a stone across the water.

GUNNER: Spot on.

COLIN HERRIETT: Firing!

Leave it.

And probably this is where the idea came from, children skipping stones across water, and some old boy on a gun crew looking at that and thinking, "I can do that with a round shot."

NARRATOR: Hugh similarly scales up his experiment and fires the balls from point-blank range.

HUGH HUNT: Three, two, one, fire!

Okay, I'm having fun. Okay.

NARRATOR: At this height, they skip easily, but from a bomber, flying so low and so fast would be suicidal.

HUGH HUNT: Three, two, one,…

Okay, that's 400 miles an hour, at 35 feet. Okay, 400 miles an hour at 35 feet... you're not going to get a pilot foolhardy enough to do it. But from a point of view of understanding what's going on, it's really helpful to know just how far away from the limits we are.

NARRATOR: He raises his stand-in airplane to a more realistic height.

HUGH HUNT: We're going to do 60 feet flying height, 200 miles per hour flight speed.

Al, off you go. Three, two, one, go. Go.

They're not bouncing.

NARRATOR: No matter how often he tries, the model bombs refuse to bounce.

HUGH HUNT: Even if we go really fast, at this height, we can't make them bounce. So we've got to think a little bit about what we do about that. We either get the planes to fly lower, or even faster than 300 miles an hour, which we can't do.

NARRATOR: Sixty nine years earlier, Barnes Wallis encounters the same problem and looks for a solution in the game of cricket. He knows that bowlers can control the bounce of a cricket ball by applying spin to it.

He tries spinning the test balls backwards as they leave the catapult.

He discovers that backspin helps the balls bounce better and travel further, even when he launches them from a height of four feet.

Hugh's cricket-bowling machine can apply spin at the flick of a switch.

HUGH HUNT: Now let's put some backspin on, see if we can get them to bounce.

Fire!

Hey, that's excellent! One, two, three, four, five bounces.

NARRATOR: The backspin pulls the oncoming air over the top of the ball. This creates an area of low pressure that sucks the ball upwards, helping it float in the air for longer and bounce better. The lift also results in air being deflected down behind the ball, which can be seen by its disturbance trail on the water below.

Thanks to modern aids like slow-motion photography, Hugh is able to gather all the data he needs after just two days of testing. It took Wallis 22 days to complete his tests, back in 1942.

HUGH HUNT: Barnes Wallis didn't have access to good high-speed photography, but we can look now, at this ball, and we can count exactly how many revs per minutes there are. We can measure the speed; we can measure the angles; we can measure everything. He didn't have access to that kind of information.

Fire!

Fire!

NARRATOR: Hugh establishes that, for a bomb to bounce after being released from a plane, it has to be dropped from the right height and travelling at the right speed, and, most importantly, it must be spinning backwards.

Like Wallis before him, Hugh works out that altering any one of these factors will affect the others. But getting them all to work together will pose formidable engineering challenges, when he mounts the full-scale trials in Canada.

Before Barnes Wallis scales up his test spheres and produces a full-size bomb, he turns his attention to his prospective targets. Among the cluster of giant dams that nourish the industrial powerhouse of the Ruhr Valley, the greatest is the Möhne. This dam alone provides most of the water.

At 130 feet high, it is composed of giant granite blocks and weighs a staggering three-quarters of a million tons, a formidable target even for the most ingeniously designed bomb.

The replica dam in Canada will be made from concrete. The structure will require four hundred and twelve individually cast concrete blocks. Like the Möhne, it will be a gravity dam, held in place by its own colossal weight.

JIM BELLAVANCE: When we've got it finished, we're going to have eight million pounds of concrete sitting here. It's a massive amount of volume.

NARRATOR: The enormous concrete wall will sit in a trench cut into a bed of blue clay. Clay is easy to dig and holds its shape, without needing to be shored up. It's also impermeable to water, so the trench should remain watertight when the lake is allowed to flood in behind the dam.

But clay has its drawbacks. When Jim starts moving in his over-sized Lego® blocks, the weather turns against him.

MAN: Look at how fast it's coming in.

JIM BELLAVANCE: It's just running oozing muck.

NARRATOR: The rainwater can't drain away through the clay barrier, and the trench fills up.

JIM BELLAVANCE: Everything was just going nicely; 36 hours of rain and it's in the toilet.

NARRATOR: More rain on the way, he struggles to finish before the aircrew arrives.

The men who built the Möhne dam didn't rely on clay foundations. They chose to anchor their structure in the bedrock. One hundred thirty feet down, inside this layer of solid granite, is the designer of the replica dam in Canada. Rick Donnelly confronts the awesome reality of the German dam. It appears unbreakable.

RICK DONNELLY: Barnes Wallis must have felt that he had a real engineering challenge.

If you look at this structure here, it's absolutely massive, designed to withstand all the water forces, plus earthquake forces and all kinds of other forces, well in excess of what man can actually produce.

I would have a lot of sleepless nights if I'd promised to try and blow this up. Because, if you look at this thing, if we drew the bomb to scale, it's, it's a peanut.

NARRATOR: Wallis wrestles with this problem. How is he to produce a bomb that is big enough to blow up the Möhne Dam, but small enough to be carried by a plane?

Wallis asks a team of engineers to build a scaled-down model of the German dam and to try to work out how to destroy it with a scaled-down bomb. They decide to detonate their bombs under water.

Explosives expert Sidney Alford demonstrates why they choose to do this.

SIDNEY ALFORD (Explosives Engineer): Three, two, one.

When the charge went off, there was nothing denser than air to maintain the pressure, so the pressure dissipated very quickly, before the pressure had time to perforate the steel plate.

NARRATOR: A little water, pressing against the charge, makes all the difference.

SIDNEY ALFORD: We now have a column of water surrounding the explosive. Since the extremely-high-pressure gas cannot escape, it will push on the surface of the steel for longer, and that increased duration of pulse will very probably push a disk out of the steel.

Firing!

Ah, anyway, you can see a considerable difference caused by the prolonged pressure pulse.

NARRATOR: With help from Hugh, Sidney recreates Wallis's experiment with a model of the Möhne dam. He wants to know how close a tiny charge needs to be to the dam to blow it up.

SIDNEY ALFORD: That's 50 grams of plastic explosive, and I propose to lower it that deep into the water.

HUGH HUNT: About 25, 30 centimeters?

SIDNEY ALFORD: About 30 centimeters.

Firing!

It's still intact.

NARRATOR: He moves his model bomb a little closer.

HUGH HUNT: It's okay.

SIDNEY ALFORD: Firing!

NARRATOR: Even with the amplifying effect of the water on the blast, it fails. Finally, they place the charge under water, right up against the dam wall.

SIDNEY ALFORD: Three, two, one.

It worked!

NARRATOR: Sidney, like Wallis before him, finds that a modest charge punches its way through solid masonry, if the bomb is placed right up against the dam wall and then detonated under water, as this original test footage shows.

Wallis now knows that a tiny bomb can bust the Möhne dam, but first it must spin, skip over nets, hit the dam, somehow hug the wall as it sinks, then detonate.

Hugh is facing a similar challenge. First he adds weight to the wooden balls to make them sink.

HUGH HUNT: Go.

NARRATOR: But how can he make them hug the dam wall as they go under?

HUGH HUNT: Fire!

NARRATOR: Again, backspin provides the solution and causes something magical to happen.

HUGH HUNT: What happened there was the backspin kept on going after it hit the dam, and the backspin brought the bouncing ball back onto the dam.

NARRATOR: The same backspin effect that keeps the ball aloft in the air, in water, pulls the ball against the dam wall.

Exploiting this effect, Wallis now has his plan. First, his bomb skips up to the dam, then backspin brings it back onto the face of the wall. Thirty feet down, water pressure activates three pistols housed inside the bomb. These fire and detonate the explosive charge.

Hugh plans a similar feat. If his pilot can hit the dam, and the dummy bomb spins down and comes to rest against the dam wall, then the dummy will be replaced with a real bomb of equivalent size.

Rick Donnelly and co-designer Alfred Breland visit their creation for the first time.

JIM BELLAVANCE: Welcome to the pit.

ALFRED BRELAND: Welcome to the pit. Hey, Jim. How's it going?

JIM BELLAVANCE: Good to see you again.

RICK DONNELLY: Hey, how you doing?

JIM BELLAVANCE: Hey, Richard. Good to see you.

RICK DONNELLY: Yeah.

NARRATOR: Jim manages to pump out the rainwater from the trench and carry on building. The structure that's taking shape represents the central section of the Möhne dam. When it is finished, it will stand 30 feet tall, a quarter of the height of the original.

RICK DONNELLY: If we added another couple of meters to it, it'd be classified as a large dam in, in the dam community, which is pretty good, if you have to build in a month. You can sometimes spend years on this kind of stuff.

NARRATOR: Rick designs the dam to react to explosive forces in a similar way as its big sister. But Jim's worried that the way the blocks lock together will make the dam difficult to blow apart.

JIM BELLAVANCE: You'd have to lift everything above there up to let it basically let the gear disengage and let it slide. So we'll have to see.

NARRATOR: By the beginning of 1943, Wallis's obsession with his target begins to deliver promising results. He manages to drum up enough support from the Ministry of Aircraft Production, to run a full-scale test of his bouncing bomb.

As this original test film shows, he is given permission to convert a Wellington to carry a wooden prototype.

It bounces perfectly.

HUGH HUNT: He thought long and hard about this so he, he was pretty sure he got the scaling from the small bombs, his small marbles, his small test balls, to the larger ones.

He was pretty sure he got that right, but being pretty sure and being sure are different things. And if you're going to be risking people's lives, if you're going to be risking people's money, if you're going to be risking these expensive airplanes, you've got to be sure.

NARRATOR: Wallis does have that confidence. But he knows that to take his idea to the next stage he must first overcome a political rather than a technical obstacle. He needs to win the backing of military planners, who are highly skeptical of reckless proposals to hit specific targets from the air.

So far, in the war, precision bombing just hasn't worked. Barely one fifth of British bombs fall within five miles of their targets. So rather than aiming at particular industrial installations, Bomber Command adopt a policy of indiscriminately peppering German cities with incendiary bombs. The brutal logic is that flattening the homes of German workers is far more effective than trying to hit their factories.

Wallis knows it's a gamble to submit his plans for a surgical strike against the well-protected German dams to the head of Bomber Command. Air Chief Marshal Arthur Harris, known as "Bomber Harris," does not respond well to civilians with crazy ideas. He dismisses Wallis's plan as having no chance of working.

But Wallis is not deterred. He convinces Harris to watch this test footage and manages to win him over.

On the 26th of February, 1943, Wallis is finally given the go-ahead. Work begins on modifying 30 new Lancaster bombers to carry his bomb.

Wallis feels physically sick. He realizes the terrible responsibility of pulling off his plan. The raid is set for mid-May, 1943, when a full moon will guide them in. By then, the extra water from the spring rains will be pushing on the dams, making them ripe for busting.

The next chapter in the story of the Dam Busters plays out beneath a ruined Norman church, on a secluded beach in Kent, in southeast England. Here, Barnes Wallis gathers his team to witness the first drop of a full-size bomb.

Wallis does not have the resources to make a large metal sphere, so he turns a steel drum packed with explosives into a huge ball by wrapping wooden staves around it. But when he tries dropping his sphere, it shatters.

It is a major setback, and the clock is ticking.

For six days, Wallis looks out onto the desolate Kent coastline—just as his statue does today—and watches his plan disintegrate before his eyes. No matter how well he strengthens the bomb's wooden casing, it continues to shatter on impact with the sea.

But the brilliant engineer turns a setback into an advantage. He sees that once the steel drums break away from their wooden casing, they continue to bounce. He decides to simply abandon the troublesome spherical shell.

With less than a month to go, he is forced to carry on with untried naked cylinders.

Before Hugh settles on the design for his bouncing bomb, he has a close look at one of the Barnes Wallis originals.

HUGH HUNT: I like the simplicity of it. It's just a simple cylinder.

I know that Barnes Wallis looked at the possibility of having barrel-shaped bombs and so on, but he ended up with a nice, simple cylinder, and simplicity in engineering is always the safest way to go.

NARRATOR: Inspired by the real thing, Hugh uses a simple cylinder for his bomb too. He orders up a scaled down version—to run some tests—and a cannon to launch it from.

ASSISTANT: Yeah, be much easier to see won't it?

NARRATOR: He knows that keeping a cylinder level as it flies through the air is not going to be easy.

HUGH HUNT: Right.

One of the issues with a cylinder is that this can wobble. Now, we can see that wobble. If I toss this up in the air, we can see…see? There's a little bit of wobble. Hard as I might try, it's very hard to get that not to wobble.

If it wobbles, then you can imagine it's going to go onto the water like…towards the water, like this. And if it hits at an angle like that, it's going to go off to one side. And the wobble will just get worse and worse and worse and worse.

NARRATOR: Hugh hopes that, once again, backspin will come to the rescue. His team inserts a special plug into the barrel to hold the cylinder sideways. Then they will spin it at high speed, in the hope of eliminating the wobble. It's the same principle that keeps a child's toy top spinning straight.

TOD TODESCHINI: All right, we're ready to start gassing.

NARRATOR: They use an electric drill to spin up the cylinder through a hole in the side of the barrel.

TECHNICIAN: Speed!

TOD TODESCHINI: Fire!

HUGH HUNT: Three bounces! What did I say?

TOD TODESCHINI: No. Did you hear, did he hear a clunk, when James dropped the drill?

HUGH HUNT: What was that?

TOD TODESCHINI: That was James doing that, as he pulled the drill out.

NARRATOR: With the drill coming away early, the bomb wasn't spinning fast enough to ensure a wobble-free flight.

HUGH HUNT: So, Tod, spin as fast as we can go. Up to 2,000 rpm? Or how fast do you reckon you can get?

TOD TODESCHINI: Two thousand? Twenty two?

HUGH HUNT: Okay. So by the time…

NARRATOR: Hugh needs to work out the minimum spin speed required to get the bomb to fly straight and bounce successfully.

HUGH HUNT: And with a higher spin speed we should get more stabilization, so it should hopefully bounce clean, more cleanly for two or three bounces.

TOD TODESCHINI: Yeah.

HUGH HUNT: Spinning up.

TECHNICIAN: Speed!

TOD TODESCHINI: Fire!

HUGH HUNT: Beautiful!

TOD TODESCHINI: Now, that one worked.

HUGH HUNT: Still spinning. Look. Still spinning.

TOD TODESCHINI: That one worked.

HUGH HUNT: Still spinning. Look.

TOD TODESCHINI: Yeah, yeah.

HUGH HUNT: Still spinning.

TOD TODESCHINI: Fantastic.

HUGH HUNT: Yellow, black, yellow, black, yellow, black.

TOD TODESCHINI: We got about six or seven bounces off that I think.

HUGH HUNT: Fantastic.

NARRATOR: After a successful day of testing, Hugh commits to the cylinder shape. He determines that a full-sized bomb will need a spin speed of 700 revs per minute to bounce well.

Hugh asks his Cambridge workshop to make a wooden prototype. Now he has to figure out how to rotate his bomb under a plane.

Wallis's men waited until they approached their targets before starting a motor to spin up their bombs.

HUGH HUNT: Barnes Wallis needed a motor because he was going to be flying two, three hours to his destination. But we're only going to be a few minutes away from our destination, so we've decided not to use a motor. For simplicity, we're going to spin the bombs up on the runway before we take off.

NARRATOR: For the trials in Canada, Hugh's team will use a power drill to spin up the bomb on the ground and hope that it keeps spinning under its own momentum all the way to the dam.

Knowing that the bomb slows down on the journey, he wants to start it off spinning at a far higher speed than 700 rpm.

HUGH HUNT: Come on. Here, put the microphone down here a sec. Can you hear the hum of it? Somewhere about...that's the hum of the... and when it gets up to 1,500, it'll go hmmmmmm.

That's 1,500 rpm.

So let's do spin down. Okay, read.

NARRATOR: Hugh allows the bomb to spin down on the bearings until it reaches the target speed of 700 rpm.

ENGINEER: Five, four, three, two, one, now.

HUGH HUNT: Ten. Seventy. Five, four, three…

NARRATOR: He monitors the dropping rev count and finds he's losing an average of 25 rpm every minute.

HUGH HUNT: Seven hundred! If our drop speed is 700 rpm, that's 32 minutes between takeoff and drop.

NARRATOR: Thirty two minutes should give the pilot plenty of time to deliver the bomb to the target, but, so far, Hugh has done his spin down measurements in the calm air of the workshop. Now he wants to find out what will happen when his bomb is spinning in turbulent air beneath a moving plane.

HUGH HUNT: The wind is going…the wind is coming that way. It's as if we're flying in that direction. And this is our bomb, and it's going to be spinning like that, so this is the underside of the aircraft. So you imagine this is the upside down experiment…and, yeah, so this is our wind tunnel—quite fun really.

NARRATOR: They blast their scaled down bomb with wind to simulate how it will behave, spinning under a plane flying at 180 miles per hour.

HUGH HUNT: So 36 is 14, 35 is 11. Straight away I can see that wind is affecting the spin down time.

NARRATOR: The wind slows it down dramatically.

HUGH HUNT: So, I've had an idea, which is to, to put some kind of protective shield in front of the bomb. So, what we're going to do now is the same test, but we're going to fix this fairing in front and see how it goes.

Thirty four is 13, 33 is 11, 35…

So it seems to be a bit better, which means without the shield, we might be stuck with only ten minutes, but with the shield, we can get up to 18 minutes.

NARRATOR: Now that Hugh knows how to keep his bomb spinning under the plane, he is ready to order up the bombs he'll use in the trials.

He decides to have them made from sections of steel pipe, closed at the ends with steel plates. Like the replica dam, Hugh's bomb will be a scaled down version of the original, one-quarter the size.

HUGH HUNT: I'm doing something which is a different scale, a lot of things differently to the way Barnes Wallis did it: different speed, different height, different size of bomb, different spinning up mechanisms. Lots of things are different, so I don't expect it to work in the same way.

NARRATOR: Hugh's bomb is considerably smaller than the Wallis original, but flying with 800 pounds of spinning metal slung from the bottom of an aircraft is still fraught with potential risk.

But the risk facing Hugh's team cannot compare with the danger awaiting the men recruited to do Barnes Wallis's flying.

As they report to a secret airfield in Lincolnshire, in eastern England, in March, 1943, the men of the fledgling 617 Squadron have little idea that they will be asked to fly dangerously low, for long hours, at night, deep into enemy territory. It takes a rare breed of flyer to do this; the mission is almost suicidal. Hugh meets one of these airmen to learn more about the operation.

JOHNNY JOHNSON (617 Squadron Veteran): The first thing that one noticed was the number of experienced aircrews there. The number of people that had, had done their first tour. Some were in their second tour. There were some that hadn't, of course, but the majority seemed to be experienced people.

NARRATOR: The squadron's commanding officer is the charismatic Guy Gibson. Although extremely young, he already has 170 operations behind him.

JOHNNY JOHNSON: When he joined 617, he was probably one of the most, if not the most experienced bomber pilot in Bomber Command, at that stage.

HUGH HUNT: At the age of…?

JOHNNY JOHNSON: Twenty four.

HUGH HUNT: That's extraordinary.

JOHNNY JOHNSON: Yeah. He was known as the "arch bastard." But he managed to get the squadron very much working together.

NARRATOR: In his welcoming address to his new squadron, Gibson is deliberately vague about the mission.

GUY GIBSON (Squadron 617 Commanding Officer): You are here to do a special job, which I'm told will have startling results. What the target is, I can't tell you. Nor can I tell you where it is.

NARRATOR: They are kept in the dark until the night of the raid. The 147 handpicked fliers are aged between 20 and 32. There are men from Britain, Australia, New Zealand and 29 from Canada.

Today, in Canada, the grand experiment is about to begin. Hugh is introducing his handpicked airmen to their target.

ALEX WAGNER (Buffalo Airways): I think it's dead ahead of you.

HUGH HUNT: Is that the dam site just ahead?

ARNIE SCHREDER (Buffalo Airways): Yeah, just right ahead.

Just below the treetops.

ALEX WAGNER: Yeah, that makes sense.

Sixty feet, yeah?

ARNIE SCHREDER: Yep.

Looks good.

NARRATOR: In 1943, 617 Squadron had six weeks to train for their mission, but Hugh's team has only six days.

ARNIE SCHREDER: What do you think, Alex?

ALEX WAGNER: It's looking good up to now.

ARNIE SCHREDER: Maybe that's the best thing we need.

NARRATOR: These modern-day dam busters are tough, fearless "can-do" pilots. Their day job is hauling freight, in temperatures of minus-40, to keep the Canadian Arctic wilderness open through the extremes of winter. Pilot Arnie Schreder has 37,000 hours to his name. He's one of the most experienced pilots in Canada.

Everybody's home for the giant experiment will be the outpost town of Mackenzie, British Columbia, which lies 400 miles north of Vancouver. Since the logging industry crashed in 2008, there are few prying eyes.

This area of Canada shares the seclusion of Barnes Wallis's test site, on the Kent coast, in wartime Britain.

Conveniently, Hugh's dam is only a stone's throw from the airport, where the team has the run of the place.

ALEX WAGNER: Air traffic in Mackenzie, it's Buffalo 5-721.

We're joining a left-hand downwind now for runway 1-6.

NARRATOR: The pilots have little idea of what they are getting into.

HUGH HUNT: I want to show you a few things about what 617 Squadron was and what they did back in 1942 and 1943. So, here's some of the trials. Here we go. Here comes a Lancaster…beautiful plane, isn't it?

And there goes a bomb dropped, and notice she lifts up.

NARRATOR: Looking at footage of Wallis's original tests, Hugh introduces his team some of the risks they will face trying to get their steel drum to bounce on water.

ARNIE SCHREDER: Oh, that one went right up on the beach.

HUGH HUNT: Look, there's a house just there. Look at the chimney. You wouldn't want that coming through your living room door.

ARNIE SCHREDER: No.

HUGH HUNT: And here we go, it's happened again. And look what happens there, the splash.

MIKEY MCBRYAN (Buffalo Airways): Yeah, it came off the plane.

ARNIE SCHREDER: Came off the plane there, I know.

HUGH HUNT: So, how high do you reckon they were flying there?

ARNIE SCHREDER: Fifty to sixty feet.

HUGH HUNT: I'm going to show you another movie clip here.

ARNIE SCHREDER: What, he's going to get…he's going to get nailed there. He's too close.

HUGH HUNT: He's very close. And look how…

ARNIE SCHREDER: Ooooh!

HUGH HUNT: Look how high it goes. Because that angle came in, you know, at five degrees or less, you know?

ARNIE SCHREDER: Oh, yeah.

HUGH HUNT: And then, what about this one? How high do you reckon he's flying there, Arnie?

ARNIE SCHREDER: Not very high, about ten, fifteen feet.

HUGH HUNT: Here we go. And then…

ARNIE SCHREDER: Ooh! Yeah.

CHUCK ADAMS: Yep, too low.

ARNIE SCHREDER: Too low.

HUGH HUNT: You, you sort of saw that coming from the previous clip.

ARNIE SCHREDER: Oh, yeah.

NARRATOR: These trials are being conducted by the U.S. Air Force. In the final months of the war, the Americans are considering using a version of Wallis's bouncing bomb to attack Japanese ships in the Pacific.

On each bombing run, they reduce the release height. By the 37th run, they come in way too low.

HUGH HUNT: What height do you reckon that was?

ARNIE SCHREDER: Ten feet. Ten feet.

HUGH HUNT: On the movie it says nine feet—nine feet, 390 miles an hour.

NARRATOR: Now the team realizes that the low flying they'll be doing threatens to be lethal.

MIKEY MCBRYAN: The biggest risk is the bomb itself. It has the ability to bounce back and hit the airplane. Now, if you can imagine 800 pounds of steel, spinning at 1,000 rpm, there's a lot of momentum there. So it'd do short work. It'd cut through this thing like butter.

NARRATOR: If anyone can do it, it's Arnie and his crew. They spend their summers dousing forest fires from treetop height.

HUGH HUNT: They are used to flying low. And we needed people who are used to flying low. Arnie told me yesterday he first took the controls of a plane when he was 14, crop dusting. And you know, probably his uncle said "Hey, Arnie, hold these will you?"

NARRATOR: The challenge is set. The grueling test flights can begin. Before they get down to business Hugh tries to fire up his Canadian crew with a rousing British anthem.

HUGH HUNT: This is the theme from The Dam Busters movie, 1954.

MIKEY MCBRYAN: Okay. It's got to be a pretty low-budget movie.

HUGH HUNT: It is a low-budget movie.

NARRATOR: For their trials they use a vintage Douglas DC-4. Beneath the modern paintwork is an aircraft built during the Second World War. It is a good model for the Lancasters used by Barnes Wallis. It has the same top speed, and can carry the same maximum payload.

The man responsible for turning this civilian cargo plane into a bomber is Ryan Beaubien.

RYAN BEAUBIEN (Aeronautics Engineer): We designed our test program to ensure that there's no stability issues, no controllability issues on the aircraft. Because when you think about it, it's not as, it's not a, a safe-sounding project. We want to fly low and drop bombs out of the aircraft.

NARRATOR: During the war, Barnes Wallis designs a beautifully simple mechanism to release his bomb. It is held between spring-loaded arms, clamped in place by friction alone, so when it is let go, it falls away cleanly.

But Ryan chooses not to follow Wallis's design. To meet exacting local safety standards it makes more sense for him to design the rig around a component already approved for dropping loads from helicopters, a special release hook.

HUGH HUNT: Okay, so when it releases, it does... and you see how that drops. That goes...

NARRATOR: This is the first opportunity for Ryan to test his rig in the air.

HUGH HUNT: Drop.

NARRATOR: Pilot Arnie Schreder is not worried.

CAMERA OPERATOR: Arnie, the moment of truth.

ARNIE SCHREDER: The moment of truth. Well, I think it'll be uneventful—hopefully.

NARRATOR: Arnie thinks this first test flight should be a breeze. All he has to do is drop a dead weight from a comfortable height.

ARNIE SCHREDER: Right, we're warming up. It's smooth.

NARRATOR: If they were going to try to skip the bomb they would have to drop it from low altitude.

ARNIE SCHREDER: We got V1. Here we go.

ALEX WAGNER: V2 plus 15.

NARRATOR: But there's to be no spinning or bouncing yet, so there's no need to fly low.

ARNIE SCHREDER: We're ready to climb.

NARRATOR: The point is simply to check that the rig will release its load cleanly, but for Hugh this is a huge moment.

HUGH HUNT: Everything we've been doing up until now has not been so critical, but now, if this drop doesn't work, we're in serious danger of end of mission.

Okay, they're coming in.

ARNIE SCHREDER: We're arming the system now.

MIKEY MCBRYAN: Okay, copy that, Arnie. And as soon as I see the bomb, I'll call, "Bomb gone."

HUGH HUNT: Ah ha.

MIKEY MCBRYAN: So this is going to be a drop.

HUGH HUNT: Hooo.

MIKEY MCBRYAN: Bombs away!

Bomb gone.

Oh hooo.

ARNIE SCHREDER: She should make a splash, eh?

MIKEY MCBRYAN: Ah that, that was a, that was a splash.

HUGH HUNT: That was a splash.

It didn't come out that clean, but it was okay. Well done, guys.

ARNIE SCHREDER: Didn't come out that clean, eh?

NARRATOR: The fliers are not quite sure what to make of it, but down on the ground, they're concerned.

HUGH HUNT: There's nothing you can do. You push the button. If it doesn't work it doesn't work.

MIKEY MCBRYAN: Oh, yeah, it's…seeing it tumble like that, first thing on my mind is something's wrong.

ARNIE SCHREDER: Oh, yeah. Oh, yeah.

HUGH HUNT: Can we do that slow?

NARRATOR: Unless they can work out what went wrong with Ryan's rig, the whole mission could end here. A bomb, dangling from the undercarriage, could be a lethal hazard on landing.

RYAN BEAUBIEN: We tested this exact bomb, on this exact rig, like, ten times.

CHUCK ADAMS: Yeah, but we're in the air now. We got different [expletive] happening.

TAMARA: It's shaking around.

ARNIE SCHREDER: She was shaking a little bit.

HUGH HUNT: Okay, so there we go. Just frame by frame. One…now this is where the bomb release goes, there. They're both moving down.

ARNIE SCHREDER: Yeah, sure they are.

HUGH HUNT: So what happens then after that?

They both move down. That's one. Next one, they're both moving down, yeah. Next one...

ARNIE SCHREDER: Coming down.

HUGH HUNT: Ahh. It looks to me as if the bomb is coming down, it pulls the cable, which pulls this up.

NARRATOR: Hugh sees that the problem lies with the cable that controls the release mechanism. It's supposed to drop the arms that hold the bomb in place down together. But, because it is too short, when it is released, as one arm drops down, the other is yanked up.

But it's too late for Hugh to redesign. He has to improvise.

HUGH HUNT: We need to have the travel from there. The extra distance we need is from there.

NARRATOR: They can't lay their hands on a longer piece of the special cable, but the steel bars which form the arms could be made longer.

HUGH HUNT: It needs to be… how much, how much longer? Four and a half inches, yeah? So we need…call it five: two and a half inches long on each side.

NARRATOR: Hugh and his Ph.D. student, Hilary Costello, visit a local workshop.

HILARY COSTELLO: Quadra.

HUGH HUNT: Quadra Machine Works.

NARRATOR: Here, they are more used to fixing tractors than bomb release mechanisms.

HUGH HUNT: These are the tie bars, and they're, they're two and a half inches too short.

NARRATOR: With an engineering problem to solve, Hugh can hardly contain himself. And he can't keep his hands off the machines.

SEAN: He's taking some work away from you.

HUGH HUNT: This is to let you know I drilled some of the holes, so…

NARRATOR: Less than two hours after identifying the flaw in the design, Hugh fits the customized bars.

HUGH HUNT: We've had to solve a few serious problems in this, along the way. That's just the way engineering is. You always have to solve problems. That's what engineers do.

NARRATOR: Over at the dam, there are also problems between concept and reality. Builder Jim Bellavance struggles to fit his oversize Lego blocks together.

RICK DONNELLY: So where do we stand? We got…there's something like…it must be…

NARRATOR: The dam designers have flown in expecting to sign off on the job.

JIM BELLAVANCE: The issue we're having, that's just killing us, is when they poured all the slope blocks, the guys didn't put the plywood down, so they're...

NARRATOR: Casting the concrete on rough ground leaves the blocks with uneven surfaces, so they don't line up properly.

JIM BELLAVANCE: And so you can see how they're out of line, now. So if I put this row on this row, and I go to put the top blocks on, you can't get them to set down.

NARRATOR: Since many of the studs don't lock into their cavities, the blocks won't sit in place. Jim decides to remove the studs that don't fit. It's a job that has tripled the time it takes to lay a single row. He now has less than five days to finish the dam. He's not sure he can do it.

It's day two of the trials. It's the second test flight, and it threatens to be the last.

CHUCK ADAMS: If there is a problem on this next drop, I guess the whole thing's going to wind up being cancelled—simple as that.

CAMERA OPERATOR: But is this one going to work?

CHUCK ADAMS: God damn right, it's going to work.

HUGH HUNT: Right, so that is now...

NARRATOR: Chuck has given them one chance to fix the rig. He can't allow another heavy bomb to dangle from the bottom of his plane, jeopardizing the safety of his crew.

Hugh's asked for the bomb to be spun up this time, not for bouncing, but to see how much rotation speed is actually lost on the journey from runway to drop zone.

To ensure they get maximum revs, they decided not to skimp on horsepower.

HUGH HUNT: That's a drill.

HILARY COSTELLO: That's a drill.

CHUCK ADAMS: Now that's a drill.

Are you ready?

ARNIE SCHREDER: Brakes are good; nosewheel steering is good.

NARRATOR: Hugh asks for 1,500 revs to start with, but Chuck's team struggles to achieve this.

MIKEY MCBRYAN: Thirteen!

ARNIE SCHREDER: I'll see what the rpm is.

Thirteen, eight.

CHUCK ADAMS: Go!

ALEX WAGNER: You got her, Arnie. Rock and roll.

NARRATOR: Even before they get off the ground, the spinning bomb starts to slow down very quickly.

ARNIE SCHREDER: She's down to 1,200 or something, already.

NARRATOR: Seven hundred revs at the drop zone would get a bomb to bounce.

ARNIE SCHREDER: Nine hundred twenty rpm, but she's going down in a hurry.

NARRATOR: But first, they must get through this safety test.

Ryan Beaubien knows that the future of the whole project now rests on his release mechanism working properly.

ARNIE SCHREDER: We're on final, and this thing has spun down 390 rpm.

This thing has spun down 390 rpm. She ain't gonna last very long.

IAN: Is this a dummy run?

HUGH HUNT: No, this is it.

MIKEY MCBRYAN: This is it.

ARNIE SCHREDER: Go ahead, when you want.

Standing by for the, "Bombs away."

MIKEY MCBRYAN: Bombs away.

Beautiful! Yes, yes!

ARNIE SCHREDER: She hit nice and flat?

MIKEY MCBRYAN: She was even as...

HUGH HUNT: And it's floating. Yeah.

MIKEY MCBRYAN: It's floating. It's still spinning.

HUGH HUNT: And it's still spinning.

Hi, I.Q.M., this is the phantom accordion player here.

ARNIE SCHREDER: Yeah, go ahead accordion player.

HUGH HUNT (On Radio): Well done, you guys. It was a beautiful release and it stayed spinning nicely. It looked just perfect. So, well done, you guys.

ARNIE SCHREDER: She went down to about 390 on that, so she's really slowing down in a hurry.

HUGH HUNT: We'll just have to work something out, but we'll be all right. We'll sort it out.

NARRATOR: A successful release, but Chuck is not happy with his contribution.

CHUCK ADAMS: We got to get more rpm out of it, though…slows down. Yeah, we've got to get it up to at least 2,000. Now, what I want to get is like a one horsepower motor, 'cause these drills are nothing but a bunch of bull [expletive].

HUGH HUNT: Good drop?

HILARY COSTELLO: Good news?

NARRATOR: For the moment, Hugh puts the spin speed problem to one side.

HUGH HUNT: Brilliant.

ARNIE SCHREDER: Dead straight.

HUGH HUNT: And you didn't feel anything, Arnie?

ARNIE SCHREDER: No.

NARRATOR: Now they've achieved a clean release, they can put their safety concerns behind them. On the next test flight, they'll see if they can get their bomb to bounce for the first time, rather than just crash into the waves.

In 1943, the Lancaster crews face the same challenge as Hugh's team. With only 19 days to go before the raid, Barnes Wallis is about to attempt to get his stripped down cylinder to bounce.

He fills the metal drum with a mixture of concrete and cork to stand in for explosives. But when he releases it, rather than bouncing, it sinks like a stone.

Wallis sees that his pilots will have to fly far lower if it is to bounce: not at 150 feet, but at 60 feet.

He puts his problem to Guy Gibson. Gibson explains that, at 60 feet, a pilot would just have to hiccup and he would land in the drink. Unaware of why they are being asked to fly so low, Gibson's men follow their leader into the sky with a mixture of excitement and trepidation.

JOHNNY JOHNSON: I'm lying in the front, and I can see the ground going past and past and past. Absolutely tremendous! It was probably the most exhilarating part of the actual flying.

On one occasion, we were coming back, and some bright nark flew underneath us. I wasn't very pleased with that, because the slipstream at that sort of height could have caused all kinds of… however we got away with it.

NARRATOR: They are ready to try from 60 feet. It works.

This original footage captures Wallis and his team on the beach savoring the moment.

Back in Canada, Hugh now wants to see if he can get his bomb to bounce for the first time. And like Barnes Wallis, he asks his pilot to fly far lower than the comfortable 150 feet he's used to. For the next test flight, Hugh wants Arnie to release the bomb from just 80 feet.

This is lower than the DC-4's altimeter can gauge with any accuracy, so Arnie must estimate his flying height by eye alone.

Hugh wants to monitor how precisely Arnie is able to do this. He asks him to fly down the center line of the runway, which keeps the plane a fixed distance from his camera. This allows Hugh to measure the plane's height from markers on a broomstick in the foreground.

HUGH HUNT: Arnie, how high did you fly on the first one and how high…?

ARNIE SCHREDER: Flew 60 on the first one and about 220 on the second one.

HUGH HUNT: Well, I'd agree with you on the second one. First one was more like 70, 75.

ARNIE SCHREDER: Yeah, well I, 70 feet or so.

HUGH HUNT: This one is the first one. Each one of these marks on that pole there is at 25 feet, so your eye level 75, bottom of the plane 70 feet. That make sense?

ARNIE SCHREDER: Yeah. That's what I said, about 70 feet.

HUGH HUNT: And the next one, okay, here we go.

ARNIE SCHREDER: Fifteen to twenty.

HUGH HUNT: Yeah, 15 to 20. I agree on 15.

ARNIE SCHREDER: Fifteen to twenty.

HUGH HUNT: Eye level is 25 feet; bottom of the plane, 20 feet, let's call it.

ARNIE SCHREDER: I said that. We'll do one at 60 to70 and the next one at 20.

NARRATOR: Forty years of low-level flying gives Arnie an uncanny knack for gauging altitude by eye. But how were Barnes Wallis's pilots to measure their height, flying in the dark?

The solution: two beams of light shining down from the plane onto the surface of the water are calibrated to converge at precisely 60 feet. Fly too high, the pools of light cross over. Too low, they don't meet. At the correct altitude they come together to form a figure eight.

The only problem: the twin spotlights make the Lancaster more visible to the enemy.

Arnie doesn't have to worry about being spotted by German gunners, but he still faces a formidable challenge. It's the third test flight. To get the bomb to bounce, Arnie will have to release it from 80 feet. But, almost immediately, he leaves behind features like trees and buildings that help him estimate his height. He'll have his work cut out over the surface of a smooth, featureless lake.

ARNIE SCHREDER: Almost glassy water.

ALEX WAGNER: Oh, yeah, exactly.

NARRATOR: Hugh modifies his broomstick gauge to monitor Arnie's flying height. The center line of the runway is now a line of buoys. Notches on the broomstick are now strings stretched between poles.

HUGH HUNT: Each one of those poles is 100 yards apart, okay? And each one of those strings is 50 foot in height.

CHUCK ADAMS: Okay.

HUGH HUNT: So the bottom one, actually, this one is zero.

CHUCK ADAMS: Yeah.

HUGH HUNT: Fifty feet, 100 feet, 150, 200, 250, 300, 350, 4.... So you'll be able to get a feel for it.

CHUCK ADAMS: Okay.

HUGH HUNT: That's the theory.

CHUCK ADAMS: Well, I would say it's going to work there, brother. Got all my faith in the world.

NARRATOR: Hugh's grid works lengthways, too, so it can also tell him the distance the bomb has traveled if it bounces, but it will only work if Arnie flies down the line of marker buoys.

They are about to try to bounce a bomb on water for the first time since the 1940s.

Arnie drops down to 80 feet, and looks for the buoys.

ALEX WAGNER: Where the [EXPLETIVE] are they?

ARNIE SCHREDER: Where the [expletive] are they?

ALEX WAGNER: I don't see them.

ARNIE SCHREDER: Well that's about 80 feet, Mike.

MIKEY MCBRYAN: Do you want me to call, "Bombs?"

ALEX WAGNER: Go ahead, Mikey. We're ready.

MIKEY MCBRYAN: Bombs away.

CHUCK ADAMS: Beautiful skips.

HUGH HUNT: Woo!

MIKEY MCBRYAN: We had three skips, three confirmed skips.

HUGH HUNT: Hey!

NARRATOR: But the flight isn't a total success. Hilary's altitude reading does not jibe with Arnie's estimate.

HUGH HUNT: Hilary reckons they're up at about 150 feet.

HILARY COSTELLO: No, higher than 150.

HUGH HUNT: One hundred eighty feet?

MIKEY MCBRYAN: Okay. I can confirm you were at 180 feet, with three bounces.

ARNIE SCHREDER: Say that again, Mikey. One hundred eighty feet?

MIKEY MCBRYAN: According to Hilary and Hugh you were at 180 feet. We'll review when we get back.

ARNIE SCHREDER: No, we weren't at 180. We were about 80 feet.

HUGH HUNT: Did you manage to line up with the buoys?

ARNIE SCHREDER: No, I didn't.

HUGH HUNT: Okay, well, look. You must be flying closer to us than the buoys. In fact, we can tell that by looking at where the bomb landed. It's way closer than the buoys.

ALEX WAGNER: Oh, there you go.

HUGH HUNT: Let's talk about it when we get back to base.

ARNIE SCHREDER: We were down at treetop level, right?

ALEX WAGNER: Yeah.

HUGH HUNT: The issue that Arnie's got is that when they're way back, they can't see where the buoys are, and by the time they do see the buoys, they can't change their line. So they've got to have something they can see from way back.

We're going to the dollar store to pick up some inflatable dinghies, kids' things.

CHUCK ADAMS: Okay, you do that.

HUGH HUNT: Yeah, and we'll…

CHUCK ADAMS: Make sure they're, make sure they're a bright color, though.

HUGH HUNT: We, we do what we can do, and that's it.

CHUCK ADAMS: Can't create honey with dog [expletive].

HUGH HUNT: That's…that would be true. Thank you, Chuck. We're done. You can't create honey with dog [expletive].

HILARY COSTELLO: All right, I think there's another store still open.

NARRATOR: Arnie couldn't see the marker buoys, so Hugh and Hilary are on the hunt for some highly visible replacements.

HUGH HUNT: Beach ball, beach balls, yeah, 60 centimeter beach balls.

"Jungle Hideaway Baby Pool."

HILARY COSTELLO: Complete with butterfly.

HUGH HUNT: The things we do for science.

CHUCK ADAMS: I've got a new name for him: "Professor Screwloose."

HUGH HUNT: Well, yesterday we were sort of getting the plane flying and serious engineering, and today it's gone from the sublime to the ridiculous, taking bloody inflatable toys out onto the lake.

Bye, bye.

NARRATOR: They are hoping that their colorful new buoys help Arnie find the line he needs to fly down.

Hugh still has the problem of the bomb losing too much rotation speed on the way to the drop zone.

HUGH HUNT: It's on the other side of the bomb.

NARRATOR: The footage of the last flight confirms the spin speed was nowhere near the 700 revs they need at the moment of release.

HUGH HUNT: One, two, three. I think it was 330 rpm.

It's fast enough to bounce, but it's not as good as I'd like it to be.

NARRATOR: Hugh has another idea. He wants to cut away some of the metal sheet, or "fairing," that protects the bomb from being buffeted by the wind.

HUGH HUNT: He's doing it already.

Hey, Chuck.

CHUCK ADAMS: What's that?

HUGH HUNT: It's called a hammer.

WELDER: Just knock in that corner. There you go.

HUGH HUNT: Hooray, well done.

I can see the air moving already.

NARRATOR: Hugh hopes that wind blows through the new opening and keeps the bomb spinning fast all the way to the drop zone.

They are four days into the test program, and, so far, they've only achieved three modest bounces. Today, Hugh wants to get his bomb to skip better and bounce farther. He hopes that this time Arnie spots the colorful new buoys and that his crude surgery on the metal fairing keeps the bomb spinning fast.

ARNIE SCHREDER: Okay, we're on our way.

CHUCK ADAMS: Jesus Christ, I thought he was going to blow me away.

RYAN BEAUBIEN: Well, that was 1,400 we got it up to, so about the same rate as last time. So we'll be able to see this time if it's going to spin more with that fairing cut out.

NARRATOR: Hugh asks Arnie to release the bomb 20 feet lower than last time. Again, this is lower than the DC-4's altimeter can accurately gauge, so Arnie must judge by eye.

One small slip at 60 feet and Arnie ends up in the lake.

ARNIE SCHREDER: Okay, I'm armed.

ALEX WAGNER: One, two, three. They're lined up. You've got them.

MIKEY MCBRYAN: Bomb gone.

HUGH HUNT: Three, four, five, six, seven, eight, nine bounces.

MIKEY MCBRYAN: Absolutely beautiful, Arnie. It looks like you were 60 feet on the nose.

HUGH HUNT: Well now, that was just brilliant. We had, I think, nine bounces.

ARNIE SCHREDER: Oh, okay. That's pretty good.

HILARY COSTELLO: How was the jungle gym?

ALEX WAGNER: It was good, we could see that one. And we got lined up with the back one.

ARNIE SCHREDER: I have it figured out. Yeah.

HUGH HUNT: We got nine bounces. It travelled for 460 meters. Arnie came in at 60 feet, spot on, which he just…you know, he knows what 60 feet means.

NARRATOR: The bomb bounced so well because it spun much faster, at 850 rpm, thanks to the opened up fairing.

HUGH HUNT: I mean, okay, I think the record that Barnes Wallis got was 17 bounces. Okay, well, that's fine. I'm happy with nine, thank you very much.

NARRATOR: Hugh feels they've solved the rotation speed problem.

ARNIE SCHREDER: Rack 'em up.

CHUCK ADAMS: Rack 'em up.

ALEX WAGNER: Rack 'em up.

NARRATOR: He now knows how high and fast the plane needs to travel and how fast the bomb needs to spin to guarantee good bouncing.

But there's no celebrating at the dam.

JIM BELLAVANCE: Okay, gang. We'll just move the boxes right against the wall.

NARRATOR: The dam was supposed to be ready by now. With only two days of flying left, they are way behind schedule and forced to cut corners. Instead of filling the joints with mortar, which wouldn't have time to set, they stuff them with rags and then add clay to make the surface smooth.

RICK DONNELLY: The idea is we've got to have a dam holding water to bust. It's literally the 11th hour, or maybe it's the 10th hour, but it's, it's getting late, and we need to make sure that the dam is properly sealed. Now these pieces of cloth we've used, they're to provide backing, so that when we put our seal on the dam, which is a plastic sheet, it doesn't have cracks and crevices to deform into, puncture, and we end up with a multitude of leaks that we can't control.

NARRATOR: As dawn breaks, they are still hard at work, but Jim's spirits are high.

JIM BELLAVANCE: We're now at…we're still not at 8:00, which is good, because I'm hoping that at the 10 to 10:30 timeframe we should be able to start letting the water in. That's our goal.

NARRATOR: It's taken Jim and his team of five men just 25 days to get this far. It's a remarkable achievement when compared to the construction of the Möhne Dam. It took more than 1,000 men five years to build. When it was completed in 1913, the Möhne was the biggest dam in Europe.

It's the day before they attack the dam. With only one practice flight left, Hugh needs to raise his game. So far, his dummy bombs are empty cylinders, light and easy to bounce. But now he's going to try bouncing a much heavier bomb, one that would sink if it were to reach the dam wall. But a heavier bomb brings with it a new element of risk.

As Barnes Wallis discovers on his beach in Kent, the heavier the bomb, the bigger the splash, and 617 Squadron rehearse with concrete bombs. Should a pilot dip any lower than the altitude set at 60 feet, the splash from the bomb could bring down his plane, as one veteran pilot found to his cost.

LES MUNRO (617 Squadron Pilot): In my case, I rather feel that I might have lost a bit of height, and that…and…unintentionally lost a bit of height, and that the splash from the water hit the rear of my aircraft, round about the, the tail. And my rear gunner was jammed in his turret, and he couldn't get out until we got back to base.

Henry Maudslay, the flight commander, his aircraft was so badly damaged, you can see bits of debris dropping off. And his aircraft was…they couldn't repair it in time for the raid itself.

NARRATOR: For the final stages of the test program, Hugh wants his steel cylinders to weigh the same as a bomb, if it were packed with enough explosives to blow up his dam. Like Wallis, he fills them with concrete.

HUGH HUNT: Excellent. Oh, they look fantastic.

NARRATOR: These bombs will certainly sink, but a third of a ton of rotating steel and concrete could shake the plane to pieces. Each one will have to be perfectly balanced.

Wallis's bombs were fifteen times as heavy, and they had to be balanced without using of any of the modern aids available to Hugh.

HUGH HUNT: Yeah, so we've got these nice little force gauges, which, when you squeeze them, they give a reading on the computer. We'll be able to measure the out-of-balance at both ends, and then we'll correct for the out-of-balance by adding weights.

NARRATOR: Readings from the gauges are fed into a computer program, written by Hugh, which helps them work out how much weight to add to each end.

HUGH HUNT: Call it a hundred minus 165. Two sixty, so we need 200 grams on that end, 100 grams on this end.

SEAN: Okay.

NARRATOR: Finally, they apply the bomb's distinctive colors. They spray on the black, but use a brush loaded with paint for the yellow.

HUGH HUNT: Here's a tin of paint, a liter, probably more than a kilogram, and we've used it to paint one, two, three, four, five bombs. So that's 200 grams of paint per bomb. With 200 grams, we're balancing these to within 20 grams.

It looks good, doesn't it?

ARNIE SCHREDER: It looks good, but it sure is ornery. I see why you went out of balance.

NARRATOR: The thick yellow paint is heavier than the thin coat of black, so one half of the bomb outweighs the other, throwing it out of balance.

HUGH HUNT: But, you know, a decision like that, you make, you know… "Let's do it with a brush." Six hours later you, you know, you regret it. And six hours after that, you're still at it.

It's not what we need right now.

NARRATOR: After working through the night to rebalance the concrete-filled bombs, they are ready to put one to the test.

Arnie agreed with Hugh that 60 feet would be on the limit of safety, but he takes it upon himself to come in even lower.

ARNIE SCHREDER: I'm about 50 feet there now.

ALEX WAGNER: You see the buoys now? The line is five degrees to the right.

NARRATOR: The bomb might be beautifully balanced, but, at this height, its splash could be lethal.

HUGH HUNT: Five bounces. That splash was high, but he was low. He must have been at 40 feet.

HILARY COSTELLO: No, just above 50.

ARNIE SCHREDER: A heavier bomb, I guess, that time. Only five bounces, eh?

MIKEY MCBRYAN: And you were just above 50 feet on that one.

ARNIE SCHREDER: Just above 50 feet, okay.

NARRATOR: All eyes are on the splash.

HUGH HUNT: You've just released there, okay?

HILARY COSTELLO: And you don't pull up.

ARNIE SCHREDER: That [expletive]'s going to hit my airplane.

Oh, yeah. Oh. It did get the tail.

ALEX WAGNER: Washed the airplane.

HUGH HUNT: Look at that, it's gone up to 80 feet, that plume.

NARRATOR: The splash is alarmingly high, but Arnie makes light of it.

HUGH HUNT: So there we go. Now let's have a look at the other one.

NARRATOR: Hugh is satisfied that this test is a perfect model for a run on the dam tomorrow.

Now his measuring gauge comes into its own. It tells him his bomb has travelled 443yards. This gives him the distance they'll need to mark out for Arnie in front of the dam.

HILARY COSTELLO: Okay, well you need to come about 13 meters towards me. And then you have to figure out if I'm lined up with the dam.

HUGH HUNT: Ryan's using a rake to rescue our jungle pool.

HILARY COSTELLO: Don't break it.

I'm just measuring how far away you are.

NARRATOR: They fix the jungle float exactly 443 yards from the dam wall, to give Arnie his release point.

HILARY COSTELLO: So, you can drop it now.

HUGH HUNT: Okay, let go now, if you like. Drop it there. Let's drop.

NARRATOR: If Arnie hits this mark, the concrete bomb should skip up the channel and onto the dam, gently kiss the wall, spin back and sink.

During the war, Barnes Wallis isn't able to creep up on the German dams and lay out floats to mark the release point for his bombers. 617 Squadron must find another way to make sure they know when they've reached that magic distance.

Simple geometry solves the problem. From reconnaissance photos they measure the distance between the towers on the Möhne Dam, then plot on the release point, 476 yards from the dam. A triangle of these proportions produces a unique aiming device.

It's a wooden triangle, with a sight at one end and pegs at the other two corners.

As a bomb aimer, Johnny Johnson trained to use the contraption.

JOHNNY JOHNSON: Give directions for where you want to go.

NARRATOR: He shows Hugh how it was done.

HUGH HUNT: Okay, Johnny. You're the bomb aimer in the Lancaster.

JOHNNY JOHNSON: Right.

HUGH HUNT: And I am the Möhne dam, and these are the two towers. And you're flying towards the dam, and you're going to release the bomb at the right time.

Over to you.

JOHNNY JOHNSON: Left, left. Left, left. Steady. Steady.

Bomb gone.

HUGH HUNT: It's just so simple. It's so beautifully simple.

JOHNNY JOHNSON: Oh, it is, yes, absolutely. It was just a question of making sure that you, you dropped your bomb at exactly the time that those two coincided with the, the towers on the dam.

HUGH HUNT: Do we need it to be accurate to within 10 feet, 50 feet or…?

JOHNNY JOHNSON: If you overshoot by 10 feet, you're going to hit the dam before it finishes bouncing. If you undershoot, it's going to drop before it should and, and explode before it gets to the dam.

HUGH HUNT: So it really is about just stopping bouncing…

JOHNNY JOHNSON: Yes, at, at the dam.

HUGH HUNT: …at the dam.

JOHNNY JOHNSON: Absolutely at the dam, so that it can roll down and explode at it, at its set depth.

NARRATOR: For the pilots attacking the Möhne dam to get close enough to release their bombs, they must evade fire from flak guns located in the towers. Aerial surveillance photography reveals some mysterious structures that have suddenly appeared along the crest of the dam. Alarmingly, they have the look of anti-aircraft rockets. It is only after the war that they are revealed to be fake fir trees, placed there by the Germans in a futile attempt to camouflage the crest of the dam.

Jim Bellavance can afford a little celebrating. He's been chasing his tail for the last four weeks, but with half a day to go before the planned run on the dam, he's done it.

JIM BELLAVANCE: Finally, I can stand on top.

That's the best walk I've made in a long time, I'll tell you.

HUGH HUNT: Are you ready to open up?

Yeah, let's open up.

NARRATOR: The most dangerous moment in any dam's life is when the water is first let in. The deeper the water gets, the more pressure it exerts on the bottom of the dam.

RICK DONNELLY: When the water gets about another two meters up there, we've got to be spending our time on the other side of the dam looking for problems and figuring out how to fix it, if they happen.

NARRATOR: Within minutes, it seems Rick's worst fears materialize.

JIM BELLAVANCE: Shut it! Close it!

NARRATOR: They rush to stem the flow of water coming in from the lake.

RICK DONNELLY: I mean, it hasn't got any worse.

JIM BELLAVANCE: Actually, the first leak is slowing up.

RICK DONNELLY: Yeah. I'll tell you what, we may as well see if it's going to seal. It's slowing down. It's not getting any worse. Open it up.

JIM BELLAVANCE: Let her go.

NARRATOR: Rick hopes that as the water rushes in, particles of silt will wedge in the crevices of the dam and seal it.

RICK DONNELLY: It's not disaster yet. The leak is slowing down, with the water going up, which means that it's starting to seal. Right now, with time, the leak is decreasing. I don't think it's going to stop. But if it doesn't get any bigger, then the dam's not in any danger, and we can still do what we need to do.

ALFRED BRELAND: It only has to last 24 hours.

NARRATOR: The fragile dam is finally ready for the raid tomorrow.

On the 16th of May, 1943, 133 men of 617 Squadron are summoned to a briefing. The detail of their mission is unveiled to them, for the first time. Barnes Wallis introduces the men to their targets—three dams in the Ruhr Valley—and the ingenious method he has devised to destroy them.

JOHNNY JOHNSON: Barnes Wallis, I think, impressed us very much.

HUGH HUNT: Did he come across as a boffin, or did he come across as somebody…?

JOHNNY JOHNSON: No, no, a man who knew exactly what he was doing, and what he was trying to do.

NARRATOR: Then many of the men get their first glimpse of Wallis's brainchild. It's not quite what they expect.

JOHNNY JOHNSON: These again were different from anything we'd seen in the way of bombs. These bloody great dustbin type things. "What the hell's that?"

NARRATOR: Each "dustbin" contains over three tons of high explosives.

At 21:39 hours, Wing Commander Guy Gibson leads the first of three waves of 19 Lancaster bombers into the sky. Wallis watches them go. It is now up to Gibson and his men.

After crossing the North Sea, they enter Fortress Europe and run into pockets of heavy German flak.

Flying at 100 feet to stay below enemy radar, two planes hit high-tension power lines and crash. Three more aircraft are brought down by enemy fire. Altogether, 34 young men are lost before they reach their destinations.

HUGH HUNT: Gee. You're in that plane for a few hours, getting to your destination, and then you have to work hard for half an hour, defending you and your colleagues and your plane and your country and, and you get home, and you, that's the day up. And then the next day, you do it again. Gee. Actually sitting in this place just makes it all feel very real.

NARRATOR: Gibson's aircraft arrive at the Möhne just after midnight. He lines himself up and flies into the flak. Four hundred seventy six yards before the target, Gibson drops his bomb.

The bomb explodes, but the dam remains intact. Even after three more bombs, the dam still holds. As the aircraft go in to attack, Gibson flies alongside to draw fire from the German guns.

They drop their fifth bomb.

Watching from a nearby house was five-year-old Karl-Heinz Wilmes.

KARL-HEINZ WILMES (Möhne Dam Bombing Witness): After the thunder of the guns and the noise of the engines, there was silence. And after the silence, we heard a rushing sound. And my Grandma said, "They've hit the dam."

NARRATOR: A 30-foot high tidal wave of floodwater courses down the narrow river valley. Bridges and buildings, roads and railways, are swept away up to 40 miles downstream.

Today, Arnie and his crew try to emulate Guy Gibson's achievement. Like Gibson, Arnie is limited to five bombs, five attempts to hit the dam. Unlike Gibson, he won't be flying at night, over hostile territory, having to dodge enemy bullets. Nor will he be carrying a live bomb.

He's not allowed to drop explosives from a civilian aircraft, so he'll be using one of Hugh's concrete-filled bombs instead. But he must still hit a tiny target, a strip of concrete only 100 feet wide and nine feet above the water level. If he manages to do this, and the bomb hugs the dam wall as it sinks, Barnes Wallis style, then he'll be rewarded with an explosion.

Hugh's team is standing by with a drum of live explosives, which they will winch into place, in the reservoir, behind the dam wall. If Arnie hits the target with the dummy bomb, the live one will be detonated.

The team is all set, but, at the last minute, a new problem develops at the dam. It's started leaking again, and the water's beginning to find its way around the sides where the concrete blocks abut the earth.

JIM BELLAVANCE: Not cool. First thing, I think we got too anxious and opened up that water too fast. Everything was going great, until that big wave came. But…wasn't my fault; I'm not the dam engineer.

NARRATOR: Back at the airfield, they wonder what's going on.

ARNIE SCHREDER: Is the dam screwed, or…?

GLENN: It's flooding, Chuck, on the side.

ARNIE SCHREDER: You mean it's washing out?

GLENN: Washing out around or something.

ARNIE SCHREDER: Holy [expletive]. What kind of a dam is this they built?

CHUCK ADAMS: So they're running around like ding dongs bow, bouncing into each other.

HUGH HUNT: Do you think it's going to silt up?

RICK DONNELLY: I'm not so sure any more. I think we got to try and help it silt up.

The fact that it's going through the dam isn't a huge problem. What I'm worried about is the two abutments, because if they start to give way, then we lose the blocks and we lose everything.

So we're going to treat the two abutments the best we can and see if we can stabilize things.

NARRATOR: Rick dumps loose earth into the pool behind the dam, in the desperate hope it is carried into the breach and will seal up the sides. But their frantic efforts only seem to be making things worse.

JIM BELLAVANCE: Don't drop it. Every time you drop it, the water goes faster. Just set it down there and mush it in.

NARRATOR: They can't risk waiting any longer.

ARNIE SCHREDER: Hello. Yeah. Twenty minutes, okay.

Okay, let's go.

NARRATOR: There might not be time for even one run with their concrete bomb, let alone five.

And, with the pressure on, it's the fliers' turn for things to go wrong.

ARNIE SCHREDER: How come it's stopped at 570? It's spooling down.

ALEX WAGNER: Do we have to go back?

CHUCK ADAMS: Yeah, we got to change this bomb real quick. The one we just put on is way out of balance. Starting to shake the b-hell around 500 rpm.

Okay.

NARRATOR: Although Hugh and Hilary had meant to prepare five bombs for the raid, they'd forgotten to tell Chuck that one had not been balanced, and by a stroke of ill-fortune, that was the one that Chuck had selected.

CHUCK ADAMS: One there. This is 6S.

ARNIE SCHREDER: Well, they should be up here doing this, because we don't know anything about these bombs.

MIKEY MCBRYAN: Do you have the numbers on them?

ARNIE SCHREDER: What's the number on this one, Chuck?

CHUCK ADAMS: This one's 3SB, 3SB.

ARNIE SCHREDER: Yeah. And you should have had some more guys up here. Like it's just, it's just Chuck and I trying to do all this ourselves, here.

MIKEY MCBRYAN: Yeah, you're right.

He's, he's a little annoyed.

NARRATOR: They've been trying to shore up the sides of the dam for nearly an hour.

JIM BELLAVANCE: Yes, there's a god. It's stopped.

The video god's on our side today. Let's get moving.

ALEX WAGNER: If there's one guy in the world who can make it happen, it's this guy, right?

ARNIE SCHREDER: Hurry up now. Come on.

Okay, we're two.

That's thirteen.

BETH: Fourteen.

ARNIE SCHREDER: Okay, she says go.

NARRATOR: After all the setbacks, the moment has finally arrived, but Arnie is worried about the placement of the marker buoys.

ARNIE SCHREDER: I think they're a little bit too far back, eh?

ALEX WAGNER: It's like he's trying to time it so that it slows down and stops at that point.

ARNIE SCHREDER: Well, yeah, I'd rather nail the dam.

ALEX WAGNER: Absolutely.

MIKEY MCBRYAN: I hear them.

HUGH HUNT: Hey! We have visual.

ALEX WAGNER: That's the point, right there. We can overfly and line up with the dam site.

ARNIE SCHREDER: I'll just do a nice turn and get lined up. I don't really see that dam, do you?

ALEX WAGNER: Keep going to that buoy.

I know where it is. We're a quarter of a wingspan to the right.

ARNIE SCHREDER: We're too far to the right?

ALEX WAGNER: Yeah, just a bit. I can see the buoys slightly on an angle.

Line it up now.

HUGH HUNT: Here they come.

ARNIE SCHREDER: There's 60 feet there now.

ALEX WAGNER: Make it work!

JIM BELLAVANCE: Absolutely perfect.

MIKEY MCBRYAN: Impact, Arnie. It was perfect.

ARNIE SCHREDER: Well you didn't think it would be anything else, did you?

Right on, Saigon!

CAMERA OPERATOR: Where'd you hit it?

ALEX WAGNER: Right dead center.

ARNIE SCHREDER: Dead center.

CHUCK ADAMS: Oh, it's beautiful. Check this out.

ALEX WAGNER: Jeez, look at that water. Beautiful, eh?

ARNIE SCHREDER: It's like a mirror, eh? It's hard to judge your height when it's glassy, eh?

NARRATOR: Arnie did misjudge his height and came in lower than he was supposed to, at just 40 feet. His plane was dangerously splashed, but luckily not damaged. And he may have released the bomb a touch late. It didn't so much kiss the dam as nearly knock it over. But it's clear that after it hit the dam, the bomb was still spinning backwards when it sank.

CHUCK ADAMS: That's beautiful. See that. You see the brick you moved?

ARNIE SCHREDER: Now, I'd like to see it blow up now.

NARRATOR: Mission accomplished.

HUGH HUNT: This really makes me appreciate what Barnes Wallis did. That spinning bomb is a precision device. Dom, dom, dom, dom. Spin just up against the dam, spin, go down 30 feet, depth fuse. Up it will go.

And from our point of view, that's, that's as far as we're getting with this story, but, really, that was only halfway for Barnes Wallis, because he had to make it work in pretty extraordinary circumstances, and it had to work first time, on that night, in May, 1943.

NARRATOR: Wallis's bomb is a triumph. Two out of three primary targets are destroyed, and the deluge released brings immense devastation. Power stations are flooded, and the water supply to industry cut off; dozens of factories damaged; 25 bridges swept away. There is a dreadful human toll too: at least 1,300 casualties. More than half are foreign laborers forced to work for the Nazis, and some are Allied prisoners of war.

617 Squadron pay a terrible price. Of the 19 crews that leave Lincolnshire on the 16th of May, only 11 return. Fifty three crewmen die.

Barnes Wallis is deeply affected. He vows never again to risk a man's life on any of his future projects.

JOHNNY JOHNSON: Gibson had a talk to him. Explained to him that we all knew, when we took off on that raid, that there was a chance that we wouldn't come back, and it was a chance you had to take, with all the operations that we went on.

NARRATOR: With their industrial powerhouse washed out, the Germans act quickly. They requisition equipment from around the country to repair the system for pumping water to the factories, and summon a huge labor force to work round the clock to rebuild the dams.

In just four months, water and power are restored to the Ruhr factories. The raid causes little long-term damage to Germany's industrial output, but the effect on Allied morale is great. The daring and cunning of the attack captivates the nation at a time when there is no good news coming out of Europe. Guy Gibson is decorated by the Queen. The tide of the war begins to turn.

Modern-day dam buster Arnie Schreder may not feel his life was in jeopardy, but it took tremendous skill to direct his bomb up a narrow channel to a dam one-twenty-fifth the width of the Möhne Dam and hit it the first time. And it took the brains and bravado of a maverick from Cambridge to provide him with the means to do it.

HUGH HUNT: He hit the one block with the red mark on it.

ALEX WAGNER: I guess we busted it, eh?

ARNIE SCHREDER: We showed those Englishmen we can hit it with the first shot!

Broadcast Credits

BOMBING HITLER'S DAMS

PRODUCED BY
Tom Cook
WRITTEN AND DIRECTED BY
Ian Duncan
EDITED BY
Paul Shepard
CANADIAN PRODUCER
Linda Hay
DIRECTOR OF PHOTOGRAPHY
Mike Coles
ORIGINAL MUSIC
Nick Dyer and Eric Cadesky
NARRATED BY
Demetri Goritsas
CAMERA OPERATORS
Andrew MacDonald
Sean Cable
Paul Vance
Tyson Hepburn
SOUND RECORDISTS
Keith Henderson
Keith Rodgerson
ASSOCIATE PRODUCER
Joe Myerscough
FIRST ASSISTANT DIRECTOR
Keith Giesbrecht

UK PRODUCTION TEAM

EXECUTIVE PRODUCER
David Dugan
CO-WRITER
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HEAD OF PRODUCTION
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Anne Bos
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EXECUTIVE PRODUCER
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GRAPHICS
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DUBBING MIXER
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SPECIAL THANKS
The District and people of Mackenzie, BC
Ulas Cilingir
Stuart Haigh
Iain R. Murray
Vicki Podgorenko
Diane Smith
David Worrow
Science Museum Library & Archives
ARCHIVAL MATERIAL
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The Dams Raid Through The Lens
NOVA SERIES GRAPHICS
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NOVA THEME MUSIC
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CLOSED CAPTIONING
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COORDINATING PRODUCER
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SENIOR SERIES PRODUCER
Melanie Wallace
EXECUTIVE PRODUCER
Howard Swartz
MANAGING DIRECTOR
Alan Ritsko
SENIOR EXECUTIVE PRODUCER
Paula S. Apsell
Produced by Windfall Films and Omni Film Productions for NOVA/WGBH Boston in association with Shaw Media, Channel 4 and National Geographic Channels
A United Kingdom/Canada co-production
© 2012 WGBH Educational Foundation/Windfall Films Limited/Omni Film Productions Limited
All rights reserved

Image

(plane over water)
© WGBH Education Foundation

Participants

Chuck Adams
Engineer, Buffalo Airways
Sidney Alford
Explosives Engineer
Ryan Beaubien
Aeronautics Engineer
Jim Bellavance
Dam Contractor
Rick Donnelly
Dam Designer
Colin Herriett
Gunnery Expert
Hugh Hunt
Cambridge University Engineer
Johnny Johnson
617 Squadron Veteran
Mikey McBryan
Manager, Buffalo Airways
Les Munro
617 Squadron Pilot
Arnie Schreder
Pilot, Buffalo Airways
Tod Todeschini
Launcher Designer
Alex Wagner
Co-Pilot, Buffalo Airways

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