In 1940, Britain was fighting for its life against the Luftwaffe. British aircraft manufacturers couldn't keep up with the huge orders placed by the British Government. So they turned to American manufacturers like Curtiss and North American. Eventually, North American came forward with their own design for a brand new aeroplane.

The prototype was brought to the Air Fighting Development Unit (AFDU) at what is now IWM Duxford. It had great potential with a low-drag fuselage and laminar flow wing. But the Allison V12 engine which powered the aircraft struggled above 15,000 ft. So the AFDU decided to try the aircraft with a Rolls Royce Merlin instead. That aircraft became one of the greatest fighters of the Second World War - the P-51 Mustang.

The P-51 could fly and fight with British and American bombers all the way to Berlin and back again. Its range was so large that it even began to replace British Spitfires towards the end of the war. On their way back from escort duty Mustangs would also take out targets of opportunity like enemy trucks, barges, and trains. By 1944 the Allies had air superiority over Western Europe, thanks in part to the Mustang.

A fighter with the range of a bomber

In 1940 in the wartime, Great Britain was fighting with its backs against the wall. All the aeroplane manufacturers were struggling with orders so overseas sources had to be looked at. The British Purchasing Company, the BPC, had an office in New York. An order was placed for Curtiss for their P-40 design, in England we call that a Kitty Hawk. The P-40 had its failings. The engine an Allison V12, a good strong engine, but only really at low altitude. But even Curtiss couldn't cope with the order and approached North American if they'd like to take on the order to build the P-40 under licence. The president of North American wasn't overly happy with that idea and approached the BPC with their own idea of a brand new designed aeroplane with the Allison V12 that was utilized in the P-40. The prototype appeared here at Duxford at the AFDU the Air Fighting Development Unit. Now that aeroplane showed fantastic potential, a low drag fuselage and a new laminar flow jet-type wing. But the aeroplane had the Allison V12 engine and above 14,000 ft the aeroplane would've probably come off second best to aeroplanes the Germans had like the Messechmit 109G and the deadly Focke-Wolf 190. So one of the clever people at the Air Fighting Development Unit said let's try it with a Rolls-Royce Merlin. Rolls-Royce were developing at the time the two-speed two-stage and intercooled V12 that was initially going into the Mk8 and the Mk9 Spitfire. The swap was made, the Merlin engine was put on the front of the prototype, the Allison was put to the side, and that airplane became the p-51 Mustang.

Archive Footage: Another outstanding example of allied aircraft design is the Mustang. The Mustang is a fighter, sturdy and very fast and here are some of these aircraft actually shooting up enemy military trains.

So with the addition of the Rolls-Royce Merlin engine, the P-51 was a superlative aeroplane. Able to fly and fight up to 35,000 feet way above the Allison engine could have done. The idea was to build a fighter that could fly at 400 miles an hour in level flight and get to Berlin and back on its own fuel. So we have fuel in the wings, fuel underneath in the drop tanks, and the auxiliary tank as well here behind the pilot seat. Secretly in the wartime, rumour has it that the tank was taken out of one Mustang and a jump seat put in its place so Eisenhower himself could survey the Normandy beaches. Obviously quite risky putting the Supreme Allied Commander in the back of a war aeroplane, but something with the speed and the range and the combat ability of a Mustang he was pretty safe.

Another feature of the Mustang, the low drag fuselage. Of course drag in a fighter aeroplane is extremely important. Indeed they found by taking off the rivets that would aid top speed performance by 10 to 15 knots. The radiator, very special. Creates what's called a Meredith Effect after a British scientist. In very, very basic layman's terms the air goes in the front, heated by the radiator, this flap can squeeze what's coming out the outside and therefore causing a little bit of propulsion for the Mustang as well.

On a traditional wing like this magnificent Spitfire here the widest part of the wing is about a third the way down. On the laminar flow wing of the Mustang, the widest part of the wing is two-thirds of the way down. So the disruption of the air is further back, therefore, causing slightly less drag. Therefore with the same engine, all be it built by license by Packard in the United States mainly, this aeroplane in a straight level flight was a good 20 knots faster than the Spitfire.

John Tilson, 610 Squadron RAF: I only had one objection to the mustang and I assumed that not being exactly a tall guy myself I assume that all American pilots must be giants. I used to sit on a yellow cushion and have a yellow cushion behind me. But it was a delight to fly. It trimmed beautifully, it manoeuvred beautifully. I almost looked upon it as the American Spitfire.

Archive Footage: The American Eighth Air Force is contributing more and more to the Allies' round-the-clock air offensive. Particularly with its heavily armed flying fortresses.

The United States Army Air Force thought that the B-17s bombing in the daytime with 10 very brave young lads on board covered in thirteen 50 calibre machine guns would be able to protect itself. Unfortunately, that was a mistake to the tune of about thirty thousand of their finest young men. Initially, the escorts of the groups of bombers based all around East Anglia was the P-47 thunderbolt. A fantastic aeroplane, very heavy, very fast in a dive, fantastic firepower with eight 50 calibre machine guns. But when they were getting to the end of the limit of their fuel they could see the swarms of Luftwaffe 109s and Focke-Wolfs waiting for the bombers that they were escorting on the way. They had to just let them go into the swarms of Luftwaffe. Until the advent of the P-51 with its drop tanks. Initially, when P-47s were replaced for the Mustangs a lot of the pilots were quite sceptical. They loved their big heavy powerful fast P-47s. But most of them, when they got into the very light manoeuvrable Mustang that could battle with anything, they soon got used to the aeroplane. When the P-51 arrived in Duxford from Christmas 1944 until the end of the war, drop tanks made out of papier-mache, very big, but very light, fitted to the mustangs could carry the fuel all the way. So in the event that they could see the Luftwaffe coming to attack the bombing formations, all the Mustangs had to do was drop their drop tanks and get into the battle. The Mustangs with their drop tanks could fly and fight all the way to Berlin and back again. Hermann Goring was actually supposed to have said when he saw Mustangs over Berlin he knew the war was lost. Towards the end of the war, the Allies held air superiority. The Mustangs were a fantastic part in that battle.

Charlton Haw, Commander 129 Squadron RAF: We only did one to Berlin. We actually went with the bombers which meant weaving all the time. When we got there we turned and came straight for home, in the meantime the Americans had gone straight there and then came weaving back with the bombers. That's how it was done and you imagine the aeroplanes in the sky over berlin it was I've never seen anything like it.

The Mustang was not only used for escort duty. Because of its fantastic performance, it could fly and fight with the best of them. A P-51D was equal to anything the Germans had in the air with a fan at the front. The Messerschmitt 109G, G6, G10, G16 and the K model at the end. Plus the Focke Wolf 190A. A mustang was also quite fiercely well-armed, with six 50 calibre machine guns, three in each wing. A 50 calibre bullet is much bigger than the British round in a Spitfire which is only a 303. Flying low on the way back from escort duty low and fast, mustangs would take out targets of opportunity. German staff cars, trains, trucks, narrowboats, nothing was safe from a Mustang travelling back to East Anglia from occupied France. Towards the end of the war the Luftwaffe had obviously got the Messerschmitt 262 swept-wing jet. Far and away in design above anything that the Allies had. However when they were landing and when they were taking off they were very, very vulnerable and Mustangs caught one or two of them in such a position.

Thomas O'Reilly, 603 Squadron RAF: What it did have is terrific what you call a dive and zoom. In other words you'd be going straight up and roll around a full 360 degrees and roll off and still fly off. With the Spitfire no matter how fast you went down, how much you shoved your throttle through, instead of flying out you'd fall out you know you'd lost your airspeed. But with a Mustang you know you had no bother at all. You keep going up and you're going like the clappers you know.

In American service obviously the Mustang is a P-51. A P-51B, C, or D. In RAF service the Mustang was basically a Mk1, a Mk2 and Mk3 and so on. And Mustang in a lot of cases started to replace the British fighters purely because of its range. Some pilots didn't like it because it wasn't maybe in some cases have the rate of climb or as manoeuvrable as a Spitfire. But had the range and certainly had the comfort. There is quite a bit more space for the pilot in a Mustang cockpit than a Spitfire. Not so much the B and C model P-51. But the P-51D a huge perspex canopy. Visibility can be the difference of life or death to a fighter pilot.

Bolesław Drobiński, Commander 303 Squadron RAF: First of all it was a little bigger plane. Very comfortable inside, the visibility was very good. Not as maneuverable as the Spitfire, but more luxurious.

Gunther Rall, Commander Jagdgeschwader 300 Luftwaffe: I flew the P-51, the P-47, the P-38, the Spitfire so I have good knowledge about these aeroplanes. Beside the flight performance of these aircraft, I mean the P-51 was an excellent aeroplane, they had very comfortable cockpits because they flew for hours. You can't put a pilot in a cockpit like we had in the Me109 and let them fly four hours he gets out as a stiff man you know. So these were very comfortable and very good things.

The Mustang behind me is painted to represent an aeroplane of the 355th Fighter Group based just down the road from Duxford at Steeple Morden. At Duxford here the 78th Fighter Group used mustangs from Christmas 1944 till the end of the war in 1945. This magnificent Mustang behind me is not the only Mustang that you can see at Imperial War Museum Duxford. We have the American Air Museum, a memorial building opened by Her Majesty the Queen and dedicated to the memory of the 30,000 United States airmen lost flying from British bases from 1941 to 1945. We have an American Mustang in there, a P-51, painted to represent that of the pilot Huey Lamb who graced us with his presence when the aeroplane was unveiled.

Charlton Haw, Commander 129 Squadron RAF: We flew straight back and I remember vividly I was joined by another Mustang, a stranger Mustang because we all sort of mixed up, with this big American smoking a cigar. We weren't allowed to smoke in our aeroplanes and I didn't think this chap would insist on flying close to me and I thought 'if he wants to blow himself up I hope he doesn't get too close to me'.

The story of the Mustang did not end with the end of war in 1945 but carried on, such was the good design of the aeroplane. Mustangs indeed served in the Korean War in 1950. After the Korean War, there were lots of Mustangs spare on the civil register and if you were wealthy enough you could purchase a Mustang. So you've got an aeroplane with 1,700 horsepower, a four-bladed variable pitch, then constant speed propeller. An aeroplane that can do 430 miles an hour in straight and level flight. You have got a serious piece of kit here. An often overused word is iconic, but I can't think of a better one. But a household name loved by both pilots and indeed families today and delighting air shows all over the world.

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