The Avro Lancaster is one of the most famous heavy bombers of the Second World War. With a wingspan of 102 feet and four Rolls-Royce Merlin V-12 engines, the Lancaster could carry the heaviest bomb load in the European Theatre of Operations. This carrying capacity facilitated one of the most high-profile missions of the war: the attack on the Ruhr valley in 1943, now known as the Dam Busters Raid, when 19 Lancasters were adapted to carry Upkeep, the famous Bouncing Bomb.

In this video, our expert tells us why the Lancaster Bomber played such a crucial role in WW2. We go inside the fuselage of Duxford’s Lancaster KB889 and take a look at the enormous bomb load of this Second World War icon.

How did the Dambusters' heavy bomber secure victory?

Graham Rodgers: “In the early parts of the Second World War from 1939 to 1941 some statistics say that only one in 10 RAF bombers in Bomber Command was getting to within five miles of its target. Those early aeroplanes - twin-engined aeroplanes, such as the Wellington, the Blenheim, the Hanley Page Hamden and the Whitley - very brave guys going around in quite antiquated airplanes. An Avro Manchester with a full crew of seven guys usually were struggling to get up to ten thousand feet and 200 miles an hour and also struggling to get off the ground with a full bomb load sometimes. Avro, the company that made the Manchester, went back to the drawing board with a designer, a gentleman called Roy Chadwick and ended up with this: the Lancaster."

Reporter: "The greatest and most powerful of the RAF's mighty fleet of bombers, Lancaster's electrified the world with their spectacular debut in the epic daylight raid on Augsburg. Here was the machine that should bring to fruition Winston Churchill's promise that Germany would be subjected to an ordeal the like of which has never been experienced by any country."

Graham Rodgers: "Now Mr Chadwick basically went back to his drawing board with the Manchester and decided he could do a lot better. So, he altered the wing spa, altered the tail slightly, and replaced the two inboard engines which were made by Rolls Royce but they were neither that reliable nor that powerful - they were called the Vulture. Mr Chadwick got rid of the Rolls-Royce Vulture engines, replaced them with four, tried tested; very reliable 27 litre v12s called the Merlin."

Reporter: "Liquid cooled Rolls-Royce Merlins - as good an aircraft engine as the world can produce."

Graham Rodgers: "With an extended wingspan of 102 feet, a wing spa to take the weight of the bomb load and four very powerful engines, Mr Chadwick ended up with an airplane within excess of five and a half thousand horsepower, capable of carrying the heaviest bomb load in the European theatre of operation, up to 20 plus thousand feet and 240 miles an hour."

Interviewer: "What did you think of the Lancaster to fly after the Wellington?"

Peter Huggins: "Oh beautiful, beautiful, it’s almost faultless I think. It's just like an overgrown tiger moth almost, you know, lovely little thing. More comfortable, warmer, more room in the cockpit, much better equipment, faster of course."

Graham Rodgers: "We are now inside the Imperial War Museum's Canadian built Lancaster KB889.So positions: you would have had stereotypically seven men, eight if there's an intelligence man on board. So, from the top you would have had on the right hand side the flight engineer in charge of looking after the engines. To his left would have been the pilot. No co-pilot on the Lancaster in the wartime not like a B-17 you just had the pilot on the left and his flight engineer on the right. Down below and further forward there would have been the bomb aimer laid on his tummy and also doubling up as a front gunner two 303 machine guns in the front turret. Coming further back now behind the pilot on the left you would have had the navigator, next to the navigator, the wireless operator for communications. Coming further back now and over the main wing spa which is very difficult to get up and over you have three: the first one covering the controls; the secondary spa; and then the third one that you have to climb up over and through to get over there. So, coming back, the mid-turret gunner. On this particular turret there are two 50 calibre machine guns. The turret is made by Martin in the United States as opposed to the earlier Fraser Nash ones with 303 British guns. Here and behind the pilot's head are the only pieces of armour plating on the entire airplane. That for crew protection is just about it. Down all the way at the bottom there: the tail turret gunner. The loneliest and most vulnerable position of a Lancaster's crew. He didn't have anything to protect him except a little piece of Perspex and towards the end of the war the piece of Perspex in front of his turret was taken out to help his field of view. But four 303 machine guns down there. He could have been the eyes and the ears and the difference between life and death for his crew."

Len Manning: "So, you had to get up in and slide down the other side into the turret. It was actually a slide, and you had two handles on the top to help you get your feet in, get you get your bottom set, on a little tiny narrow seat, and then shut the door into the turret so you completely enclosed, and that was it, you were stuck there until you you got back."

Interviewer: "Did that make it quite lonely?"

Len Manning: "Oh yeah you were really lonely stuck out the back there that's right. We just had to keep watch out watching out to make sure that you weren't attacked by fighters, but at night that was quite difficult because when it's dark it is dark you can't see a lot anyway. I know that my attitude was that being that it would be very difficult in the dark to recognise a plane then you'd shoot first and ask questions afterwards."

Graham Rodgers: "The fuselage, the skin of the Lancaster that is .7 of a millimetre thick it would not stop a bullet of any calibre. The heavy machine guns from a Messerschmitt 109G; or a Fockerwolf 190 would go straight through here, straight through me and straight through the other side of the airplane and continue on their way. And both of those aeroplanes I just mentioned were also armed with cannons, which would rip a Lancaster to pieces. The lights that you see in here are just here you can see me and inside our Lancaster. Can't have on at 20,000 feet over Berlin at midnight; it'd bring every night fighter for miles. Just one other thing: you have four 27 litre supercharged V-12 engines, five and a half thousand horsepower and we're basically in a big tin can. So you have a dark, deafening, freezing and lethal environment."

Hugh Parrott: "The wireless operator was in the middle of the wing and that's where the heat came in, so was nice and hot, in fact too hot, and everybody else was very cold. I don't remember the op but we were hit by a flack, which made a very nice hole in the floor of the aircraft, not a particularly big hole but the slipstream came through, and it's the first time I've been there with my feet frozen - literally ice because the sweat in the flying boots froze up - and the rest of me was hot from the heating coming in from the aircraft, and my knees were sort of in between the two."

Graham Rodgers: "So here we are underneath the cavernous bomb bay of a Lancaster. This behind me here is a standard average of what a Lancaster would carry into battle every night. So, we have a 4,000lb bomb called a Cookie, which is 4,000lb on its own. Two one thousand pounders, two five hundred pounders, two 250 pounders over here, and the horrible things in these wooden boxes here are called incendiaries: a stick about that long, about that wide and they are horrible. The Germans dropped a couple of hundred thousand of them on us and we returned the offer with a couple of million on them. But a Lancaster because of its design and its huge, cavernous bomb bay could be adapted to carry specific bombs to destroy a specific target. Mentioning Barnes Wallis, an extremely clever engineer at Vickers, now he designed three specific bombs: Tall Boy, Upkeep and Grand Slam. A Tall Boy bomb: one bomb, the nose of it would be pressed up against the bulkhead here and the tail of it would be two-thirds of the way down the fuselage there down the bomb bay. Now a Tall Boy bomb could get through 10 feet of reinforced concrete.

A Grand Slam bomb - like a Tall Boy only bigger - a grand slam bomb's nose would be up here. The B special Lancaster designed to carry it wouldn't have bomb doors like this one because the tail of the bomb would be hanging out the other end of the bomb bay, about 30 feet down there. Now that bomb dropped from height would spiral on the way down because it had altered fins at the tail hitting supersonic speeds that thing could get through 18 feet of steel reinforced concrete. The third weapon that Mr Wallis invented was very special indeed that was code named Upkeep. Upkeep was the famous bouncing bomb. Germany was using hydroelectricity to power their steel mills in the wartime. Hydro. Water. Millions and millions of gallons of it all held in the Ruhr Valley in Germany. All that water was held back by three huge hydroelectric dams. The Mohne Dam holds back three times the amount of water as the great Hoover Dam in America. Now Wallis realised that if you break the dams not only will you cause widespread flooding in Nazi Germany but if you take away the water, they can't make hydroelectricity; if they can't make hydroelectricity they can't power the steel mills that make tanks, bullets, bombs and guns. But - how do you break the dams in 1943?

Mr Wallis came up with this idea: an idea of a four and a half tonne back-spinning mine full of Torpex explosives, thrown low and fast at the dam. To throw something that big at the dam, the only thing available that could carry and throw that thing was the Lancaster, with its 5,500 horsepower and its huge carrying ability. But of course when you're flying very low and fast you need a very special squadron. Bomber Harris in charge of Bomber Command picked a young go-getting wing commander called Guy Gibson to form a secret squadron called Squadron X at the time.

Hand-picked pilots from all over Bomber Command: Mickey Martin, John Hopgood, Les Monroe, Dinghy Young, all gathered at Scampton in Lincolnshire, and practice and practice and practice, down low, down to 60 feet. The raid itself came and the intelligence report said that the Mohne Dam was only lightly defended. That report was incorrect, the Mohne Dam was very heavily defended. Gibson, leading by example, went in first into the Mohne Dam. The flak was arcing towards Gibson's head, but he kept going faster and faster up to 230 miles an hour at 60 feet eventually bomb gone. It worked. Skipping over the water at 230 miles an hour but it fell short slightly of the dam."

Joseph Sumpter: "You left your intercom on so the everybody in the plane could hear what was being said. You heard Gibson say "I'm going in now", and you saw him dive down and run over the dam and all the flack and the gun started firing at him and he dropped his bomb I don't know, well, nothing happened anyway he just saw the big spout of water. When he got back, he said “come in number two you can go in now”, and that was Mickey Martin and while Martin was doing his run Gibson flew alongside him to try and draw the flack."

Graham Rodgers: "The Mohne Dam eventually fell, as did the Eder Dam, but that raid cost the lives of 53 young lads. But between 1939 and 1945 Bomber Command lost 55,573 fine young men.

Our Lancaster, registration KB889, came to Duxford in the early ‘80s I believe. KB889 was part of a training squadron in late 1944, early 1945. A new crew got together and went on one training flight. KB889 was flying along, and the pilot managed to fly it into a cumulonimbus cloud and the Lancaster was turned on its back. Obviously Lancasters aren't made to do a barrel roll and the middle turret gunner, he was so scared he bailed out. But the pilot managed to get the airplane righted again and landed it safely. But of course, it had to be stress tested and by the time all the rivets were stress tested in the airframe, the war was over. So back it went to Canada, and it took part in quite a bit of coastal patrol over there and saved quite a few lives. So instead of killing lots of people, it saved quite a few.

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