Dan Snow's History Hit - Dan Explains: The Dambusters Part 1

Episode Date: May 9, 2023

On the night of the 16th of May, 1943, 133 RAF airmen in their iconic Lancaster bombers took off from England, and headed for Germany. Armed with specially designed 'bouncing bombs', the highly-trained crews were tasked with interrupting German industry by destroying three enormous dams in the Ruhr Valley. It was a risky mission of unprecedented precision, from which over a third of the aircrew would never return. The Dambusters Raid, as it came to be known, is remembered as one of the greatest feats of daring and airmanship in British military history. In this two-part Explainer, and with the help of the late, great RAF veteran Johnny Johnson, Dan delves into the crew's preparations as well as the events of the historic raid itself.Produced by James Hickmann and edited by Dougal Patmore.You can take part in our listener survey here.If you want to get in touch with the podcast, you can email us at [e-mail], we'd love to hear from you!

Welcome to Dan Snow's History Hit. Eighty years ago, on the night of the 16th to the 17th of May, 1943, there was a full moon. An unusual night for a bombing raid. Usually, British bombers avoided a full moon by which they could be seen, but this was a highly unusual raid. moon by which they could be seen, but this was a highly unusual raid. 133 men in 19 heavily modified aircraft, carrying huge, untested bombs that bounced. The target were some of the biggest and most important dams in Germany. This is the story of the Dam Busters.

To mark the 80th anniversary of that raid, this is my special explainer. We're very lucky that we're able to feature an interview I conducted a few years ago with the last Dam Buster, Johnny Johnson, who tragically died last December at the ripe old age of 101. tragically died last December at the ripe old age of 101. On that 10th run, we were down to 30 feet. And when I said, bomb gone, thank Christ came from the rear turret just like that. And of course, it was so low, it was nose up straight away,

so I didn't see the explosion. But Dave did in the rear turret. and he estimated that the Tower of Water went up to about a thousand feet. The so-called Dam Busters Raid or Operation Chastise, to give it its official name, became the most famous, the most celebrated aerial strike of the Second World War. Its importance was as much a matter of morale as actual disruption

to the German war effort, as I'll explain. But it was a hugely innovative raid. And it's a raid that I think is really the forebear of all the precision strikes that are now the holy grail of strategic bombing. Rather than being a clumsy area weapon, this raid showed that bombs could be dropped from fast-moving aircraft with extraordinary precision. And that's one of the many reasons why, 80 years on, this story still needs to be told. This is Dam Busters 80. T-minus 10. Atomic bombs dropped on Hiroshima. God save the king. No black-white unity till there is first and black unity. Never to go to war with one another again. And liftoff, and the shuttle has cleared the tower. It's the 16th of March, 1943, about two months before the Dam Busters raid, a 24-year-old pilot

was summoned to the HQ of RAF Bomber Command's five-group headquarters in Lincolnshire. It's a funny-looking building. It's called St Vincent's Hall. It's a gothic revival mansion in Grantham. I've been there today. it's now in private hands, but much of the downstairs still feels like a strange 19th century stately home, but in quite a compact fashion. There were buildings, there were outhouses and temporary structures around the building in the garden, so it felt like a buzzing place, the centre of Britain's bombing effort against occupied Europe. As I sat there in the echoing, columned, high-ceilinged marble hall, I could imagine the young man also sitting, waiting to be summoned to see a bigwig,

I think mostly wondering why the hell he was there. His name was Guy Gibson. He'd already survived two tours of duty. He'd flown over 150 missions. The fact that he's still alive at this point of the war is pretty surprising. He's finally called to meet probably the second most important RAF bomber command officer in the country, Sir Ralph Cochrane, who says, how do you feel about one more flight? Gibson replied, what kind of trip, sir? And Cochran said simply, a very important one. Possibly the most devastating raid of all time. I can't tell you any more. It's like the beginning of every single heist film.

One last gig. Gibson noted down later that he thought he was being asked to go on a raid that night. And so despite all his reservations and concerns, he just said simply, I haven't got my flying kit with me. Cochran said, no, it's not tonight. You've got two months and you're going to have to form your own squadron. Gibson asked about the target and Cochran replied, I can't tell you any more than that at the moment, I'm afraid.

Guy Gibson now had a mission. He just needed planes and men. Three days later, Gibson arrived at RAF Scampton. I've been there many times. It's closed now, very sadly, and it hadn't changed that much. I've been over the last 20 years. It's one of those heritage sites that we took for granted. Gibson's office was still there, now demolished. The same wartime construction that you recognise on airfields right across the UK. The same mowed lawns, the same type of hangars. It was a grass strip back in 1943.

Gibson had to build a squadron. That's 21 crews. 21 aircraft with 147 pilots in them. It was so secret, it didn't have a name. It was known as Squadron X. One of the myths about the Dam Busters, it was a kind of elite unit. It was a sort of Avengers endgame of all the best crews in the RAF. That's not exactly true.

Some of them were. Big Les Munro, he was New Zealander with 17 missions under his belt. He arrived and he looked at all the gallantry medals on people's chests and he saw there were a lot of very good aviators there. But lots of people didn't want to sign up. Their jobs are already dangerous enough without volunteering for a super special mission. And so some other squadrons sent crews they were trying to get rid of. They were sort of volunteered by their squadron leaders. And so you get a mix. Some of them, like George Leonard Johnson, known as Johnny Johnson, had plenty of operational experience.

He'd completed one operational tour of 30 flights. He'd been given time off after that. And during those operations, he'd experienced engine failure, enemy night fights, of course, anti-aircraft fire. In fact, as he told me a couple of years ago in an interview, his career almost came to an end before it started. A failure. The first one, I was flying with one of the squadron flight commanders, and

we were carrying the 8,000 pound bomb. And nobody had successfully dropped one of these up to that stage. And we were going to do it. So we took off and went on board. Flying across the North Sea, I was in the middle of a potterage. Swung round. I see petrol streaming out of one of the engines. I called up the captain. Oh dear. I'm sorry chaps, we'll have to go back.

So we didn't drop the 8,000 pounds either. We just landed with it. So long. However, by that time, 97 had been re-equipped with Lancasters and they were looking for the seventh member of crew, the bomb-aiming, and they were training them locally. And since it made a difference between seven and six and 12 and six a day, I thought I'd have a go at that. So I re-trained as a bomb-aiming and came back to 97 as a spare bomb-aiming.

I re-trained as a bomber man and came back to 97 as a spare bomber. The RAF did eventually assign this new squadron a number, 617. And it was about to become the most famous squadron number in RAF history. Gibson, like his squadron, has become the stuff of legends. He was an extraordinary aviator, but he was hard. He seemed to manage up slightly better than he managed down. People above him loved him, but some of those who worked for him thought he could be an overly hard taskmaster. One veteran reported he was a sort of little bugger who was always jumping out from behind a hut to tell you your buttons were undone. Another described to me once how on a kind of drunken night, sometimes he would

get sort of bundled out of the bar in a kind of military form of industrial action. He had had a very difficult childhood. He'd been abandoned by his father. His mother was an addict. She was imprisoned briefly and she died when he was pretty young in a terrible alcohol-related death. But his single-mindedness was clearly vital to the formation of this squadron and the ability to carry out that raid. Six days after agreeing to lead the mission, and with no idea where he was heading at all, Gibson was driven to a golf club in a requisitioned car. There he met a scientist, one of Britain's most respected aircraft designers, the archetypal boffin. His name was Barnes Wallace. He was in his

40s and he'd made a career working on airships and then aircraft. Now he was particularly interested in bombs. Barnes Wallace looked around and Gibson reports that he made sure no one was listening. And then he said, I'm very glad you've come. I don't suppose you know what it's for. Gibson replied, no idea, I'm afraid. To which Wallace said, what, you mean they haven't told you the target? Well, that makes things awkward, very awkward. So Guy Gibson can't be told the target, but he does have the security clearance to learn about the weapon. Barnes Wallace thinks he's invented a new kind of bomb. He shows Gibson some film. It shows a bomb skimming across the surface of a lake before coming to a stop next to its intended target. Barnes-Wallace had watched his kids skimming stones on a beach and the idea struck him. He'd

also then taken his kids back home and done an experiment with them, one of the classic experiments in British history. He'd skimmed marbles along the surface of a paddling pool. The problem is, all of those marbles, and indeed the prototype bomb, had been launched effectively at surface level. They'd been shot or fired with elastic bands, for example. The problem he faced now was that he had to get an aircraft to deliver that bomb, and that meant getting the aircraft ridiculously low. Wallace asked Gibson if he could do it, and Gibson said it was difficult, but worth a try. Gibson left this meeting assuming that there was going to be an attack against the fortified U-boat pens on the French coast where the German submarines operated with such devastating effect in the Atlantic, or perhaps

the mighty and well-defended battleship Tirpitz in the Norwegian fields. Either of those operations would be very dangerous indeed. Gibson got back to Scampton, he jumped on the bonnet of a car, gathered his men around him, and he announced that they had been chosen for a very dangerous mission that anyone who didn't want to come could pull out, return to squadron, and there would be no stigma attached at all. No one moved. They all stayed where they were. Shortly after, Gibson is then summoned to Cochrane's office in the HQ of Bomber Command. He finds three large crates in Cochrane's office. In them, he's told,

are models of the target. They get their screwdrivers out and they open up the crates. Gibson actually experiences a wave of relief as he finds not a model of Tirpitz, but of some dams. 617 Squadron were going after the dams of the Ruhr, Germany's industrial heartland. And that industrial heartland needed lots of water and lots of power. The reservoirs and their hydroelectric dams provided both. The biggest was the Mona Dam, 130 feet high, half a mile long. It had been the biggest dam in Europe when it was built, just for the First World War. The problem with dams is they might be very long, but they're very thin indeed. They're very hard to hit, flying a bomber horizontally from thousands of feet up in the air, which is traditionally how you bomb targets on the ground in this period. That's why an entirely new approach

needed to be invented, and invented fast. They had to strike them in May because they'd be full to the brim after winter rains. Any later and breaching them wouldn't really have the same effect. Barnes Wallace was certain these dams were the sort of choke point of the German war industry. He calculated it took 150 tonnes of water to create a tonne of steel. So he thought, let's go for the water, not the steel. Now, one of the most remarkable dam buster related adventures I ever had was staggering through reasonably thick wood in Hertfordshire. In it, I was looking for an extraordinary wartime relic. It had been built in the winter of 1940-41. All I had to do was listen for running water, and I found it.

It's a miniature dam blocking a little stream. Still doing that job today. Little pond behind it. It's a perfect scale model, 1 50th size, one of the target dams of the raid. They then tried blowing it up over the winter of 40 to 41, and they calculated that 30,000 pounds of high explosives near the dam might do the job. The only problem with that was the heaviest bomber then in operation, a Lancaster bomber, the British Lancaster, could only carry about 4,000 pounds worth of bombs at that point of the war. So way off. But the scientists discovered that if the bomb could be delivered snug to the wall of the dam,

30 feet down, underwater, then 7,000 pounds might do the trick. Suddenly, you're getting nearer what the Lancaster could conceivably carry. The problem though with that is that you've got to get it right next to the wall of the dam. And the Lancaster's accuracy at this point of the war is, well, not as good as that. So Barnes Wallace had come up with this theory. He conceptualised the bomb. He created a four-ton bomb. Three of those tons were high explosives. It would be the heaviest bomb ever dropped from a plane. But now he'd also have to modify the Lancaster to carry it. He'd have to take a lot of weight out and he'd have to sling the bomb beneath the Lancaster as it wouldn't fit in the bomb bay. They got rid of the upper turret. They also had to take a lot of armour plating away, which the crews were absolutely thrilled about. And as I

mentioned, the bomb, codenamed Upkeep, was so big that half of it actually hung outside the fuselage. Now, the man in charge of the strategic bombing campaign, RAF Bomber Command, was Air Officer Commanding-in-Chief Arthur Harris, Bomber Harris. He was sick of scientists coming to him promising him silver bullets to win the war, shortcuts, clever little hacks. And he wasn't super impressed with this raid. It was a suggestion for a raid using a bomb that hadn't been tested fully, didn't really exist yet, carried from an aircraft that hadn't been designed for the purpose. did fully, didn't really exist yet, carried from an aircraft that hadn't been designed for the purpose. He called the Dambusters plan tripe beyond description and said there is not the smallest chance of it working, but he was prepared on this occasion to give it a go.

Gibson didn't have to worry too much about those high politics, but he did have to worry about how his crews were going to get this bomb to the target and drop it in the right place. They would have to learn to fly the Lancaster not at 20,000 feet, but at treetop height. And they started on the 31st of March 1943. There are endless stories of close scrapes, of farmers going crazy as animals were terrified in the fields below. They often arrived back with undercarriages festooned with branches. Here's Johnny Johnson with a few memories of that training. And did you drop this strange bouncing bomb in training or was the first time never dropped?

No, we didn't even spin it, but that comes later. But we started off with our only means of navigation was map reading and bed reading. Navigator and bomber mage had a map with a track marked out, and the navigator would indicate what I should be seeing. If I saw it, that was fine. If I didn't, I picked out something else equally prominent, and he could adjust his course if necessary on that. The

bombers had to make their own bomb site and it consisted of a triangle of plywood with a peg in each angle but the distance between the base pins had to be specific and the distance from the base, the apex, had to be equally specific. And on the bombing range, they arranged two poles specific distances apart. And the practice was that Lyman added a single pin to his eye and directed the pilot until the two base pins were in line with the two poles and dropped the bomb. Practice bombs, I used to add.

And if you got it right the first time, great. If you didn't, you did again, and again, and again, until you got it right. Until we got to the stage where I think most of us were fairly accurate with our bombing. But we were also using some of the dams in this country for bombing practice. Most notably Derwent Water in Derbyshire. And it had towers, so we could use those for sighting. It also had a marker in the reservoir which showed where the bomb should drop. And you use the same approach as you did on the range. And if your bomb dropped close to that marker, that was fine. You listen to Dan Snow's History at There's More coming up.

You listen to Dan Snow's history, there's more coming up. Hello, I'm James Rogers and over on the History Hit Warfare podcast, I bring you cutting edge military histories from around the world. Why was Sitting Bull such a remarkable leader? What was Napoleon's greatest ever battle? How did the Cuban Missile Crisis almost turn the Cold War hot? And who dropped the world's largest nuclear bomb on the Arctic? Through interviews with world-leading historians, policy experts, and the veterans who served, we find the answers to these questions and so much more. So come and join us on the History Hit Warfare podcast, where we're on the front lines of military history.

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who were rarely the best of friends, murder, rebellions, and crusades. Find out who we really were by subscribing to Gone Medieval from History Hit, wherever you get your podcasts. By early April, the crews were now practicing over water. They chose the Derwent Reservoir in Derbyshire in particular

because of the similarity of the dams and some of the topography to the German targets. The locals were in for quite a shock. It was a quiet part of the world and suddenly they found their roof tiles becoming dislodged, a drop of milk and egg production as the animals got spooked, and of course nobody could tell them anything about why their little valley, their reservoir and dam, had been selected. I've flown from bomber country, from flat Lincolnshire to Derwent at very low level, and you move from that flat east coast country to the pretty sudden uplands, the so-called Peak District, which is the southern extremity of the Pennines,

which for those people listening abroad is a range of, I wouldn't say mountains, but a hilly country that divides England kind of in half. The big challenge back then and the challenge for me when I was navigating this small aircraft is navigation. When you're that low down, you can't see that much. And the towns, lakes, the roads, the features, they blast past you and are gone. So you have to keep your finger moving on the map and your eye on the ground constantly, otherwise you can lose touch of the way you are. That's one great advantage of flying really high, you can see more of the earth below you. Their job was to try and hit a raft in the lake, and largely they failed to do so. Their bomb aiming gear is set up to work for horizontal bombing from 20,000 feet.

It's pretty useless when you're blasting along at 240 miles an hour on the surface of the lake and try and release your bomb to hit a small raft bobbing about below you. It is very, very hard, and it was about to get much harder because they were going to switch to doing it at night. Guy Gibson went first. He navigated his way up to Derbyshire and he did a few runs down the valley. He couldn't tell where the water was and he very nearly crashed. He pulled up at the last moment. His bomb aimer shouted over the radio, bloody hell, this is dangerous. Now had Gibson crashed then, I think it's pretty clear the raid would have been called off. It would have had huge repercussions. So they've got about six weeks to go. Guy Gibson's almost killed himself and his crew and they have no idea how they're going to pull this off. Then, in early April, Gibson gets a knock on the door. It's another

boffin, a scientist, who's come to help. Wing Commander Charles Dan. He says he's got a way of helping with the aiming. For the bouncing bombs to work, not only would they have to be dropped from a height of 150 feet, according to Barnes-Wallace, but the dams had to be exactly 1,350 feet ahead. But fear not, Dan said, he'd invented a sight. And it's an extraordinarily simple invention. It really is just a few bits of wood knocked together. You can make one at home, if you found yourself needing one. It's a sort of Y shape, and then at the end of each branch of the Y, there's an upright. So when you look along it,

you see the towers of the dam that line up with the uprights on either arm of the Y. At that exact second, it meant it was time to drop the bomb. I was flown down the reservoir by a former RAF Red Ares pilot, about 180 miles an hour, so slower than Lancaster's. And actually, even a Muppet like me, I was able to use that wooden sight and I was able to drop my notional bomb to within about 10 meters of the correct drop point. So in terms of the bomb needing to be dropped at the right distance from the dam, that sight went a long way to solving that problem. The next problem, though, was trickier. the dam, that site went a long way to solving that problem. The next problem though was trickier.

How on earth do you judge that you're flying 150 feet above the surface, above the water, when the instruments you have simply lack the precision to give you that level of accuracy? Again, this is a story of elegant, simple, but clever solutions to seemingly insuperable problems. And although the air crew rightly are remembered for their tenacity, their heroism, their sacrifice, we should also remember those scientists, those engineers who made this possible and celebrate something in the human spirit that allows us to turn our brain to problems and overcome them. Something we need plenty of still today. A scientist at the Ministry of Aircraft Production came up with a neat idea. Two spotlights mounted on either side of a

Lancaster at carefully calculated angles that meant that as the plane got lower and lower to the ground, they would form a figure of eight when the plane was exactly 150 feet off the water, which was the altitude they thought they needed to drop the bomb at. It worked. So they've got the height sorted. They've got the distance from the dam at which they want to drop the bomb, but they don't actually have a bomb yet that works. On the 13th of April, there was a test at Reculver in Kent. I've been there and stood on the beach where Barnes Wallace and Gibson watched in a state of nervous tension as a prototype bomb was dropped from an aircraft. Would it hit the white floating buoys, or buoys, as you might say in North America? No, it didn't. It completely shattered on impact.

Wallace groaned, oh my god, and Guy Gibson actually thought they had a breakdown. A few days later they were back on that same stretch of beach on the north coast of Kent. There's remains of a 12th century church, rather handsome. Some of it has eroded into the sea and that church was itself built within the confines of a Roman fort and a Saxon enclosure as well. So as they made history, they were standing in the shadow of millennia of history. But this time they made history in the wrong way. Again, the bomb went all wrong. They either sank immediately or their casings shattered. But on one of the bombs, the cylindrical core of the bomb skimmed, and that gave Wallace an idea. Originally,

he thought the bomb would have to be a perfect sphere like his children's marbles, but he thought he would try and work with this cylinder shape that might skim more easily when dropped from an aircraft. There was another test in mid-April. A cylinder was dropped this time and it sunk immediately. With 23 days until the raid, Wallace asks Gibson for a meeting. Wallace has got a further request, and this cannot have been easy for him to ask this. He shows Gibson some maths he's been doing. He's come to the pretty shocking conclusion that for the bomb to skim properly it can't be dropped from 150 feet that's too high it has to be dropped instead from 60 feet he says to gibson can you fly 60 feet from the water gibson thought about it he knew that was just ridiculously low i mean one

false move and they were straight into the water. But then he replied coolly, we'll have a crack at it tonight. This is probably the bit where we remind ourselves that the Lancaster had a wingspan of around 100 feet. So this is a crazy flying height. Gibson uses the spotlights now set up to optimise for 60 feet and he discovers that the system still works. He thinks he can fly his men at 60

feet over the surface of the reservoirs. The plan can be made to work if the bomb responds better to being dropped from that height. On the 29th of April, with 18 days to go before the May full moon and the date set for the raid, Gibson and Wallace go back to Reculver in North Kent. Now I should say, on one of these occasions, I can't work out which one, but Gibson actually had a plane crash. He crash landed in a field as he was popping down from Scampton to Reculver for one of these tests. But you get the sense that was all in a day's work. An event that would be life-changing for any of us was almost a casual remark in a diary for Gibson. A furious farm act to deal with a field

that had been gouged up by Gibson's plane on a bumpy landing. But anyway, that's a side note. It's the 29th of April and Gibson and Wallace are standing on that beach, just a stone's throw away from that Roman fort. And they're watching the Lancaster coming in at 60 feet. The bomb is released and it bounces once, twice, it bounces six times. It goes 2,000 feet. Barnes Wallace, the quiet, staid British engineer, goes absolutely bonkers. He starts waving his

handkerchief around and dancing. Gibson is so surprised he decides to join in the dancing too. and dancing. Gibson is so surprised he decides to join in the dancing too. The bomb works. Now they have to make enough of them. It was six days before the raid that the bomb, codenamed as said Upkeep, arrived at Scampton. But there are also some concrete filled dummies that the men can train with. Bear in mind the men at this point still had no idea where they were heading for. They were trying to make sense of their kind of weirdly modified aircraft, their constant low-level night flying, as Johnny Johnson reminds us in this clip. Did you have any idea what the target was then, what you were practising on these, what did you think it was? We didn't think. Too young to worry about anything. That was another thing. How old were you at this point? At that stage, I was 21.

But at this stage, when we first joined the squadron, one of the things that struck us was the experience of the crews. Most of them had done one tour. Some were on their second tour. The next thing was the aircraft, especially aircraft. Yes, a Lancaster of a court. Gnome is up a turret and it seems as though the bomb doors were sealed and there's these two legs standing down one either side of the fuselage in the front just below the nose, just behind the nose. What the hell was that for? And then the bomb arrived. It was just like

a glorified big dustbin. But at least it indicated to us what those legs were for. They obviously were going to carry that bomb when it was loaded onto the aircraft. And that was as far as we got with it. We went through training with the cross countries, bombing practices, and then we went into a twilight situation where the front perspex of the cabin and the nose were covered in blue sheeting and the pilot and the bomber wore night vision glasses. And that created a twilight situation. What I never understood was how you were supposed to map read over the North Sea,

because one of our turning points was over the North Sea. However, you had to hope like hell, you crossed our point, our coast, and the right place, and you hit the right place as you came back on dead reckoning. And from there, onto bright moonlight night flying. It had to be bright moonlight. Until we got to the stage where Gibson thought

we were fit to go. We still had no idea what the target was. He had, he'd been told by then. from the greatest millennium in human history. We're talking Vikings. Normans. Kings and popes. Who were rarely the best of friends. Murder. Rebellions. And crusades. Find out who we really were.

By subscribing to Gone Medieval from History Hit. Wherever you get your podcasts. There were so many near misses. One crew got it wrong and they nearly engulfed their aircraft in water. With three days to go, half of the crews haven't even dropped a dummy in training. The forecast is good. The skies are cloudless. Then the Air Ministry gets in touch.

Just when they thought they didn't have much time left, their raid was brought forward 24 hours. They had even less time to prepare. The day before they were about to fly, Guy Gibson was rocked by personal tragedy. His dog was run over, a close companion. Now this to many people might sound a bit weird, but it did seem to have a profound impact on Gibson. Barnes Wallace thought that Gibson might not be able to go on the raid. He was so distraught. And I think all we can say is that we don't really understand what it takes in your early 20s to survive so many brushes with death. He was in a very unhappy marriage. He'd had a traumatic

childhood. That dog meant a huge amount to him. And the death of his dog was seen as something that could seriously derail the successful execution of this raid. Gibson was miserable. He got up early on the 16th of May 1943. He'd been unable to sleep. A terrible mixture of stress, of emotions from the loss of his dog, and also from savage gout in his feet meant that he'd slept very, very badly indeed. He refused to go to the doctor to take medication for his gout, by the way, because he was worried that it would just shave a little bit off his reaction time. He couldn't risk it. He attended the burial of his dog outside his office, and then he checked out the loading of the upkeep of the bombs onto the Lancasters that were going on that morning. The aircraft were all in

the hangars. These enormous bombs were being ratcheted up into the bomb bays. Each of the Lancasters had been designated, for example, P for Popsi or F for Freddy. The crew of P for Popsi were on board their aircraft doing last minute checks, tinkering with things. And one of them pressed the bomb release button. And the calipers holding onto the bomb, which is three tons of high explosive, snapped back and the bomb smashed into the floor of the hangar. People ran for their lives. And unfortunately, the bomb didn't detonate. If it had blown up, it would have obliterated the hangar and nearly all the aircraft and many of the crews of 617 Squadron. But thankfully, it didn't go off. At 6pm on the 16th of May, 1943, Gibson called them all together. 133 men assembled. For the

first time, Barnes Wallace was there. It's the first time he met the men. And he turned to Gibson and said, I hope they all come back. And Gibson, who knew very well that they weren't going to all come back, replied, it won't be your fault if they don't. Johnny Johnson remembered the briefing so vividly, nearly eight decades later. On a Saturday night before the raid, we met as a quadrant. The majority of us really met Barnes Wallace for the first time. And he explained, showed us film of his development of the bomb, how it had been developed,

how difficult it had been to get it right in the first place. And then he told us something about the bomb itself. It weighed 9,000 pounds, of which 6,500 was explosive within that bomb, fused with two depth fuses to explode at a depth of 25 feet, but also fused with a self-destruct fuse. 25 feet, but also fused with a self-destruct fuse. And we learned out, subjectively, why. And then I think it was probably the highest powered briefing I attended throughout my operational career. The AOC was there.

Station Commander Gibson, of course, was there doing the briefing. Barnes-Wallace, doing the briefing, Barnes was also in the briefing too, senior officers of armament and engineering from the station were there, intelligence officer, and the dear old mate Nan was there too. Well, Gibson explained the trip to us. The first thing we saw, of course, when we got in the operations room, was that the two models were there,

one of the Moon and one of the Zopa. One on the Ada hadn't been completed. It obviously wasn't there. The models of the Danes. Yes. And that was how we found out what the target was going to be. How wrong can you be?

On the previous evening, after Barnes-Wallace's talk, the conjecture was it was going to be German battleships, notably the Tirpitz. Because when you dropped that bomb, it was being rotated at 500 revs a minute backwards.

Yes. And it had been dropped from exactly 60 feet at a ground speed of 200 knots. And so it became a sort of four men flying of the aircraft, navigator watching the lights and when they can up or down until they were coincident, that was the exact height, flight engineer watching the speed and indicating when it was up or down,

and the bomber directing the pilot to the target. It meant the pilots were being told by three other members of the crew how to fly the aircraft, but they didn't seem to complain too much about it. And that was the way it was going to be. And Gibson, in the briefing, explained that he would take off with two others

and they'd head for the moan and they would attack the Moan when they got there. Six others in two threes would follow him and they too would head for the Moan and if the Moan hadn't been briefed by the time they got there they would attack that under Gibson's direction. And when that was briefed, they would move over to the Aida. That was nine of the crews briefed. Five, of which we were one, were briefed for the Zorpa. And of course, the Zorpa had to be different from the other two.

It had no towers, so there was nothing to sight on. And it was so placed in the hills that a head-on attack was virtually impossible, certainly extremely difficult. And so we were briefed. We had to fly down one side of the hills with the port outer engine over the dam itself with the port outer engine over the dam itself and fly along the dam and estimate to drop the bomb as near as possible to the centre of the dam. With the port engine over the dam, the bomb obviously was on the water side.

We were a big disappointment because we weren't going to use any of the bombing practices we'd been doing for the last six weeks. But that was what we had to do, so that was the job. It's strange, isn't it, that when they heard for the first time that it was the dam, they were actually pleased. It was a lot better, they thought, than the Tirpitz or the French U-boat pens, which would be suicide missions. There was a sense that they had a sporting chance. The plan was for 19 aircraft to fly in three waves.

The first wave, led by Gibson, would fly to the Mona Dam. Joe McCarthy, known as Big Joe, was an American aviator. He'd signed up to serve in the Royal Canadian Air Force before the USA had joined the Second World War. He was Johnny Johnson's pilot, and after some initial concern that he was American, Johnny Johnson came to respect him enormously. He would lead the second wave, he would take a slightly shorter route, and he'd attack the Sorpa Dam. A reserve of five aircraft was going to meet any survivors of the first two and head for a third dam, the Ida. After that briefing, they were given a luxurious wartime meal of bacon and eggs,

both in very short supply. They wrote their final letters home and they collected their kit. Even then, we can only imagine how they were feeling at this point. But Johnny Johnson suggests there was still time for a bit of a laugh. Went back then to the messes for the usual operational bacon and eggs meal before you went. That was a time when, in the science mess, some wit would say to a captain like him, if you don't come back and I have your sausage. But that sort of thing was taken in good form.

At 8pm that May evening, the men lounged on the grass outside the hangars for a few precious moments. Somebody went up to Gibson and asked him if he needed anything, and he replied, just a lot of beer for when we get back. And then he added grimly, hopefully. Two of the pilots, Dave Shannon and Hoppy Hopkid, were standing slightly out of the way, maybe behind the hangar and smoking and quietly chatting. Hoppy was a very experienced pilot. He'd flown dozens and dozens of missions, but he had a real sense of foreboding on this one. Shannon recalls that

he said, I think this is going to be a tough one and I don't think I'm coming back. At 8.30pm, and I don't think I'm coming back. At 8.30pm, Gibson clambered into his Lancaster, named G for George. Joe McCarthy and Johnny Johnson climbed into T for Tommy. At 9pm, a red flare shot up into the darkening sky. The aircraft revved their engines, darkening sky. The aircraft revved their engines, moved into positions at the end of the strip, and took off. Operation Chastise had begun. To find out how the dam busters raid went, join me next time on Dan Snow's History. You'll be hearing more from Johnny Johnson as he describes the terrifying low-level flying across Europe, the attack on the dams, getting back, and what it all cost to both sides. See you then. you