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The World War Two bomber that cost more than the atomic bomb

The slot machine flip flapBoeing B-29 was the most advanced bomber of World War Two, and more expensive to design and build than the atomic bombs it dropped. It also helped influence the airliners we fly on today.

It was two years before Japan’s attack on Pearl Harbour dragged the United States into the war. But the US Army Air Corps was looking for a new bomber aircraft. What they were after was a "superbomber", capable of flying up to 2,000 miles (3,200km) at a time and at altitudes never achieved before.

The aircraft they got would go on to drop the atomic bombs on Hiroshima and Nagasaki and ultimately bring an end to World War Two. It would also pave the way for a civil aviation boom that led to the everyday air travel we have today.

This is the story of how an aircraft that cost more than the entire Manhattan project – the B-29 Superfortress – changed the world.

It was January 1940 when the US Army Air Corps (USAAC) approached five American aircraft companies with the request to build a bomber bigger than anything the world had ever seen. Although the US was yet to enter the Second World War, in Europe it was already raging: Nazi Germany and the Soviet Union had only months earlier invaded Poland and divided it between them. The US knew it was a matter of time before it might be dragged in.

The aircraft the USAAC wanted would have to fly further and higher than any aircraft that had yet been built. That turned out to be an enormous challenge, even for the world's biggest industrial nation.

Two of the companies approached, Douglas and Lockheed, soon abandoned work on their submissions due to the problem it posed. Boeing, however, had a head start, having begun work on a design as a private project a few years earlier.

Boeing's XB-29 design eventually won the USAAC's competition, but it would be another four years before the aircraft that became known as the B-29 Superfortress entered service.

It was the most expensive and complex industrial project US industry had ever undertaken and would not be surpassed until the space programmes in the 1950s and 1960s. And it pushed aviation technology almost to the limit.

The B-29 project became the most expensive of the entire war – costing nearly 50% more than the Manhattan Project that built the world's first atomic bombs. In today's money the aircraft, from design to completion, cost the equivalent of $55.6bn (￡41.2bn).

The bombers that Boeing and other plane makers built for the first few years of World War Two tended to carry out their missions above 20,000ft (6km). The higher you fly, the longer you can fly, because the air is less dense, but it presented the crews inside the planes with many challenges.

"You have to be on oxygen the whole time," says Hattie Hearn, the curator of the American Air Museum in Duxford in the UK. "Within two minutes of not being on oxygen you probably lose consciousness, and that was a real common thing that air crew had to had to consider. They had to have electrically heated flying suits, all this other gear which is going to be impeding movement. Very cumbersome, if you had to escape, for example. Often you could get too hot, and then that would again impede how you operated, if you're sweating, and then suddenly that sweat freezes."

Conditions were bad enough at 20,000ft. At 30,000ft, the height the B-29 needed to fly, they would be even worse.

Boeing turned to a promising new concept: pressurisation. This meant the plane's cabin had the same air pressure and oxygen content you would find on the ground – which meant crew didn't have to fly with oxygen masks. The air would be pulled out of the engines, cooled, purified and then pumped into the crew compartments. It could also be reheated so the crew didn't have to wear bulky flight suits.

The technology had been under development since the 1920s, but the concept was still relatively experimental. The B-29 would become both the first bomber aircraft and the first mass-produced aircraft to be pressurised.

"Allowing a crew to operate in light flight suits, because the compartments are heated, that allows them to take these long missions in a much more hospitable way," says Jeremy Kinney, a curator at the Smithsonian National Air and Space Museum in Washington DC.

Pressurising the aircraft's entire hull would be both difficult and expensive. Instead, Boeing devised three separate pressurised compartments for the B-29's 11-person crew. The first compartment in the nose of the aircraft housed the pilot, co-pilot, bomb aimer, navigator, radio operator and flight engineer – the latter responsible for monitoring the airplane's four enormous, temperamental engines. Between the first and second crew compartments – and above the first of the plane's massive bomb bays – was a tunnel that the crew members could crawl through. The middle compartment, where the gunners and radar operator worked, even had a chemical toilet and some bunks to nap on.

"There were some risks involved," cautions Hearn. "If you suddenly had a loss of pressure and you're in the tunnel moving between the different cabins, you could be shot out pretty much as fast as a bullet, which is a bit of a worry."

The high speed of attacking planes in World War Two meant gunners often only had a split second to pick a target, especially if they were approaching from the front. In 1944, fighters were getting faster. The B-29's pressurised compartments let designers think outside the box, and they came up with a novel concept: remote-controlled turrets.

Gunners no longer had to point the guns themselves, hoping for a lucky hit as fighters flashed by at hundreds of miles an hour. Instead, a new fire-control system calculated the gunners' aim using a radar that could account for both air temperature and bullet drop. It was the first time an aircraft had a gunsight that wasn't actually physically connected to the gun it is firing. The master gunner could even take over control of certain guns if one of the gunners was incapacitated.

"It's the last major system in which all the different angles and approaches to the aircraft are covered with guns," says Kinney. When the B-29 was no longer in danger of being attacked, the turrets could be pulled back into the aircraft to reduce drag.

The aircraft's other innovations included three sets of wheels – called tricycle landing gear – which are commonplace on airliners today.

The B-29's long missions at great heights meant the aircraft needed four very powerful engines. The designers turned to an 18-cylinder behemoth built by engine maker Wright called the R-3350 Duplex Cyclone.

In order to cut down the amount of drag, the designers made the engine housing more aerodynamic. But this starved some the R-3350's rear cylinders of air needed to cool down properly and made engine fires more likely.

The engine issues didn't take long to make themselves evident; the aircraft's first flight in December 1942 had to be cut short after one of the four engines caught fire. Worse was to come. In February 1943, the second prototype, flown by Boeing's chief test pilot Edmund T Allen, crashed near Seattle due to an engine fire, killing all 11 crew, 20 workers in a meat processing plant and a firefighter.

"The idea of the air-cooled radial engine is being pushed to its limit by the time it's installed in the B-29," says Kinney.

The radial, air-cooled R-3350 would later go on to power some of the first successful post-war airliners, but only after some serious refinement.

The B-29's engines were far from the only problem. Getting the aircraft into production was a gargantuan industrial project, requiring four separate giant factories across the US. Hordes of new aircraft construction workers had to be hired, many of whom had never built aircraft before, says Kinney. The scale and pace overwhelmed Boeing, especially at their factory in Wichita, Kansas, which was making the planes for the first B-29 bombing group.

One of the USAAC's top generals, Hap Arnold, was told to find a solution. Arnold visited Wichita in January 1944 and told factory bosses that he wanted 175 bombers ready by March. Not a single one was ready two months later.

The bombers had been built by hand because the factory was also making other aircraft on the assembly line, and the B-29s differed in hundreds of tiny details. No B-29 in those first batches weighed exactly the same, a worrying state for such a highly complicated aircraft. Only 20% of the "finished" aircraft could be flown out of the factory. Badly fitted windows and observation panels bled air or were distorted, and many electrical plugs in the plane's 16km (10 miles) of wiring didn't work properly.

Arnold set in place a rescue effort that became known as "The Battle of Kansas", bringing in experienced aircraft builders from other factories to oversee the work. The B-29s were stripped down and rebuilt so they were fit to fly. The work included fixing 568,000 electrical plugs and making dozens of changes to the aircraft's engines.

Arnold's plan worked, and after five weeks gruelling work, the first B-29s took off for the long flights to their new bases in south-western China to be used against Japan.

The B-29 had entered service in a little over three years since design work began. "It's very quick, even for World War Two standards," says Kinney. Just the pressurisation technology alone should have taken five years to develop.

The first B-29s were flown from a base behind Allied lines in China's Chengdu province.

The B-29 was only ever used in the Pacific, as shorter-ranged bombers were deemed enough to continue the war on Germany. Most B-29s flew their missions from Pacific Island bases that got ever-closer to Japan.

Flying them from these humid, makeshift air bases, such as those in the Marianas in the middle of the vast tropical ocean, was supremely difficult. One former flight engineer, Fred Carl Gardner, recounted the effort on a website published in the early 2000s. Part of his job was to monitor the engine temperatures, scanning gauges with "red-lines" where the temperature became too hot. "On a hot day, I would watch those temperatures climb past the red-line to the very limit of the gauge," he wrote. "I had no idea how hot those cylinder heads got."

Pilots would retract the B-29's landing gear as quickly as they could to reduce the strain on the engines, but after take-off, the B-29s had to fly for miles at lower power so the engines didn't catch fire.

One of the most controversial missions B-29s carried out – months before the atomic bombs were used – was the indiscriminate bombing of Japanese cities, using incendiary bombs that quickly set alight wooden houses.

The loss of life was shocking. The B-29 raid on Tokyo on the night of 9 March 1945 is thought to have killed as many as 100,000 people, making it more destructive than either of the atomic bombs that were to follow.

After World War Two, B-29 continued to fly as bomber within the newly created US Air Force (USAF) in Korea in the early 1950s. It also took up other roles, including being one of the first air-to-air tankers, which could refuel other aircraft in flight. "The B-29 is the [perfect] platform for that right. It's big. It has these two big bomb bays you can convert to carrying fuel," says Kinney.

As the Cold War deepened in the 1950s, the US and its Allies discovered that some B-29s that crashed in the Soviet Union after their missions over Japan had been used to help the USSR develop their own atomic bomber – a reverse-engineered copy of the B-29 called the Tupolev Tu-4. It was a Tu-4 that dropped the bomb in the first Soviet nuclear test, and represented the biggest nuclear threat to the West in the 1950s.

The B-29's effect as a terrifying weapon was without doubt. Kinney says that the B-29 had other, more benign influence in the years after World War II.

Boeing had built a large aircraft almost completely out of aluminium, with a high-aspect wing (long and narrow so that it reduces drag) big enough to fit four engines, and had brought aircraft pressurisation from a promising experiment to mass production. It represents perhaps the zenith of the propellor-driven aircraft before the era of jet engines began to take over.

"The B-29 is the most advanced propeller-driven airplane in the world in 1945, it encompasses all of those innovations," says Kinney. These innovations that would lead to the dawn of a new era of civil aviation.

The B-29 was used as the foundation for the 377 Stratocruiser, Boeing's first large airliner with a pressurised cabin. It was able to carry 100 passengers and hints at the larger airliners that followed in the 1950s. "At the time, Pan American World Airways is staking its future, no longer on flying boats, but, tricycle-landing-gear, propeller-driven airliners," says Kinney. He says one of their most famous posters at the time is of a Stratocruiser and the Eiffel Tower, showing that people can board an aircraft in the US and step off in Europe. "This idea of that becoming, you know, a global network of aviation routes, what international airlines are going to be. It starts with them."

The B-29 has also had effects on the ground, too. "By virtue of the World War Two being a global war, that's when you start having around the world paved runways, paved airfields." The runways built for the B-29 are especially long, as the aircraft needed about 1.6km (one mile) to take off. These long runways would help lay the foundations of a global airport network for the civil aviation boom of the 1950s, says Kinney.

Of the nearly 4,000 B-29s built in the 1940s, only 22 survive today, including two examples still flying at airshows in the US.

One of only two outside the US sits inside the Imperial War Museum's American Air Museum at the former RAF airbase at Duxford in Cambridgeshire, UK. The aircraft is called It's Hawg Wild, with a cartoon of an aggressive wild pig on its side. It flew dozens of combat missions not in World War Two, but in the Korean War a few years later.

It's Hawg Wild was flown from the US in 1980, after the plane had been lying for years in the Arizona desert, says Hearn. The museum had been looking for an example to exhibit, and learned of a discarded plane that was sitting in a "boneyard" of surplus aircraft in Tucson, Arizona. "But the big problem was getting it here. This aircraft hadn't flown for at least 20 years, and it was very big to have to dismantle and then ship over," says Hearn.

A contractor offered to bring the aircraft back into flying service, so it could be flown to the UK under its own power. The long flight was a major logistical exercise. The plane first had to be restored just enough so that it could be flown from Tucson to a US Navy base called China Lake in California, where more serious restoration work could be carried out before the B-29 was able to carry out the flight.

"Amazingly, it still had the dust from the desert on it," says Hearn.

"It seemed to be quite a risky, risky prospect, so the motorway was closed when it landed [at Duxford]. You definitely wouldn't get away with that nowadays," says Hearn.

The B-29 is a huge plane, especially compared to the other World War Two aircraft it shares space with at the museum. The tip of the B-29's giant tail fin is as tall as a three-story building.

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Walking around the aircraft with Hearn, it's easy to see how the aircraft was such a leap forward from aircraft from only a few years before. Outside the museum sits a B-17 Flying Fortress, thousands of which flew from airbases in the UK during the war. You can see the two gun positions on the side where the gunners – swathed in bulky flight suits – pointed machine guns into the open air in temperatures as low as -50C (-58F). The B-29 seems like a spaceship in comparison. On It's Hawg Wild you can see the "blisters", the bulging circular panels that the aircraft's crew could look out of, that resemble something from a submarine; the benefits of pressurisation.

The B-29 "just really shows you what can happen in the crucible of conflict, how technological advances could happen so quickly", says Hearn. "The B-29 is kind of the grandfather of modern-day aviation, I think."

The B-29 is an aircraft of two faces – a formidable war machine that played its part in humanity's most destructive moments, but also a masterpiece of innovation that shaped modern air travel and helped to shrink the world.

* The Boeing B-29 photographed at Imperial War Museum Duxford is on loan from the?National Naval Aviation Museum at Pensacola, Florida.

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