Dornier Do X: The Largest, Heaviest, and Worst Flying Boat

At the turn of the 20th century, air power was just beginning to revolutionise the world forever. Meanwhile massive cruise liners carried people across the planet in luxury. And in the middle of it all, one man dared to dream: What if these two incredible technical achievements could be combined into the largest flying ship ever built?

Well, then you’d have the Dornier DO X. A boat that could fly and that pushed the very boundaries of what was possible in engineering. A massive marvel that mystified people wherever it went, and an antique that has influenced seaplane designs to this day. But soon we may discover why this long dead legend may not be truly dead after all. This is a story of ingenuity, of the inescapable passage of time, of war, and of one man’s impossible dream.

When Worlds Collide

So, what is the Dornier DO X? Is it a ship? Is it a plane? Surprise! It’s both. The Dornier company, owned and founded by Claudius Dornier, engineer extraordinaire, built the most ambitious, heaviest and luxurious flying boat that the world has ever seen at the time.

Seaplanes had existed for decades, but not like this. The Dornier DO X is more like a medium-sized ship with a wing, engines and a tailfin. If you look at it from the front, it’s unmistakably a flying boat. We’re not exactly sure where the boat parts end, and the plane parts begin. The terms “flying boat” and “seaplane” will be used pretty interchangeably here, because the DO X defies easy categorisation.

The thing to mention about the Dornier DO X was that it wasn’t just any plane, it was absolutely massive. At almost 40 metres, or over 131 feet long, and with a 47 metre, or 156 foot wingspan, it’s directly comparable in size to a Boeing 767-300 jetliner. And the 767-300’s first took flight in 1986, almost 60 years after the Dornier DO X first did.

Nobody at the time would have seen anything like this. Even the Spruce Goose, at one time the largest airplane ever built, didn’t take flight until 1947. And as a seaplane, the Dornier DO X was truly unique.

Bear in mind at this point, we were only about a decade further on from the Red Baron flying around in a biplane, it was barely over 20 years since the Wright brothers took flight in Kitty Hawk, North Carolina. So, imagine something the size of a modern day jumbo jet flying around that also looked like a boat at the time. It would have made bystanders think the damn end times were coming.

And the Dornier DO X did indeed fly despite its gigantic size, just not very easily. It was powered by 12 separate Bristol Jupiter radial engines that were mounted across the top of the aircraft on the wings. You might be confused to see propellors facing forwards and backwards here, but that is actually by design. Each block is made up of two engines, one facing forward and the other facing backwards, in what’s known as a “push-pull” configuration.

The forward facing engines “pull” air into the propellors, which moves the aircraft forwards, whilst the backwards facing engines “push” the air behind them to create more forward thrust. This was helpful if one or multiple engines failed, as the others would still work.

This wasn’t the only thing that made the Dornier DO X a modern marvel of engineering. It was constructed during an era where external wires, biplane layouts and wood for external structures were highly common. The DO X had a pretty modern construction by comparison. Its wings were composed of a steel-reinforced aluminium-copper alloy, which were then covered by a heavy linen fabric and aluminium paint for waterproofing.

It even had strut bracing with limited wires and fuselage-mounted sponsons for greater stability.

But its design had a few teeny tiny drawbacks. The engines were prone to overheating, and because the vehicle was so heavy, with a consistent weight of over 50 tonnes, they could barely drag the DO X to an altitude of about 425 metres, which as planes go really isn’t very far off the ground. It definitely would have turned a few heads, with it flying so low over cities and buildings that the pilot could probably see the horrified expression on your face as this 50-tonne missile soared through the sky.

And because of its engine setup, the layout of the plane isn’t exactly what you’d find in modern aircraft today. Below the cockpit is a bridge like on an actual ship. Behind the cockpit is a navigation room, and behind that is the engine room. Inside it, an engineer would adjust the power of each of the 12 individual engines as was needed for the flight and also monitor the 12 separate gauges for those engines, in a very similar manner to how engineers on ships would alter their power.

The pilot would send an engine order telegraph to the engineer, who would then carry out their instructions. There was also a radio room so the plane could make contact with ground crews.

That was on the highest deck. Yes, because this really is a marriage between air travel and sea travel, the Dornier DO X was modelled off of transatlantic cruise liners at the time and had multiple decks. The main deck was where passengers would sit, but this is not your standard budget airliner. There was no crying baby behind you while you’re stuck in the middle seat between two people hogging the armrests.

No way José, this was a classic air-cruise liner, and so passengers travelled in luxury compared to airlines today.

There were tables and comfortable chairs, so high society individuals could lounge drinking a nice set of tea during their flight. Additionally, there were also leather armchairs, as well as sofa-like options. Some of the seating could even be converted into sleeping compartments for overnight flights.

But if you’re not the type to snooze whilst flying, the Dornier DO X had something for you too. There was a dining room on the main deck in case you got hungry, as well as a smoking room and a fully stocked bar. Sure, there was no in-flight movie, but a newspaper would manage just as well.

Behind the passenger spaces was an all-electric area for storing and serving food to the dining area, bathrooms and a cargo hold. All of this was replete with luxury Persian carpets and the richly decorated interior you would expect from a 1920s cruise across the Mediterranean. The DO X was built for its luxury.

Lord knows it certainly was not built for its practicality. One likes to think that they had the option to make it lighter but chose not to, because what kind of a respectable 1920s gentleman would fly in a boat without some mahogany upholstery.

One deck further down and you had the fuel tanks, which housed thousands of litres of the stuff. There are disputed numbers on just how much fuel the DO X could hold, with sources saying 12,000 litres all the way up to over 20,000 litres. Given that the Dornier was able to travel across the Atlantic Ocean even despite its thirsty engines, we will just say that the amount of fuel it had was “enough” for long-haul flights.

It also had nine water-tight compartments on the lowest deck, only seven of which were required for full floatation. So yes, just like a ship, if the Dornier took on water in one of those compartments, it could be counter flooded on the other side to keep it stable. As far as we know however, this was never required throughout its life.

It does beg the question: Why build something like this? Something so impractical, so massive, so strange?

Well, as mentioned, seaplanes are nothing new. Granted, this blurs the line between plane and boat so much that we’re not really sure whether to call it a seaplane or a flying ship, but there were a number of reasons why a combination of the two might have been built. One reason as good as any is simply to see if it could be done.

No plane had existed on this scale yet and the ambition to see if a truly humongous plane for the time would even fly could have led to great commercial success. Airships existed, but we were only around a decade away from the Hindenburg proving why they weren’t such a great idea anymore. Dornier was a visionary in that respect, he saw planes as the future, citing their reliability for long distance travel being better than airships.

If an airship went down over the Atlantic it was a potential life-threatening disaster. If a seaplane or flying boat had trouble, they could simply land in the water. No dramas.

Many seaplanes use this concept today, in areas like the South Pacific and across Oceania where island hopping by plane is much quicker and easier than building bridges between islands sometimes dozens of miles apart. Similarly, with something like the Dornier DO X, you didn’t even have to build an airport, as photographs of it landing in the river Hudson prove. Just find the closest patch of water to the city you’re aiming at and have at it.

There were barely any regulations for air travel then compared to what we have today, so if you could land somewhere safely, and then taxi to shore, what was the harm? And also, weather wasn’t as much of a disadvantage for something like the DO X. Whilst it wasn’t able to fly above the clouds because it was so heavy, which did subject it to the weather beneath them, the whole plane was already built for the water.

So, it may have been a little turbulent, sure, but at least the thing could actually fly in the rain when other aircraft would have been grounded.

In the end, only three of these beautiful machines were ever built. The first, known as the DO X1, was used as something of a promotional vehicle for the company, flying all over the world presenting itself to the masses. The other two, creatively called the DO X2 and X3, were used by the Italian navy, although these last two had slightly different specifications to the original, being slightly larger and with different engines.

But what is the story of Dornier and how this “sky-boat” came to be? Why, if it had so many upsides, did it not see commercial success? And where did the DO Xs eventually end up?

The History of the Dornier DO X

Claudius Dornier, mastermind behind the flying ship and the Dornier company, was a naturally smart guy. He completed his studies in engineering at Munich Technical College at the end of the 1900s, and being interested in those newfangled “planes” everyone was talking about, he looked for a position at an aviation company. Claudius eventually landed himself a position at the German Zeppelin factory at Friedrichshafen, eventually catching the eye of Count Von Zeppelin himself, becoming his chief scientific advisor.

He mainly worked on the use of new lightweight metals for the frames of the airships, but Dornier always had more of an interest in planes and how these brand-new alloys could be used in fixed-wing aircraft. He designed the first all-metal plane in 1911 and the Count permitted him to open up his own division of the company: The Dornier Aircraft Works.

When World War One broke out in the 1910s, one can imagine Dornier had some reservations around the whole thing, coming from a German mother and a French father. But he was loyal to the Kaiser’s kingdom, building and designing airships and planes that were used throughout World War One. But on the 11th hour of the 11th day of the 11th month, the last bombs fell as Germany surrendered and the Treaty of Versailles came into effect, which severely limited Germany from building any planes at all. And that is where the Dornier DO X’s story really begins.

To circumvent the Treaty of Versailles’ restrictions on the German aviation industry, Dornier, who had gained full control of his factory after the war, moved operations just over the border to Switzerland, at a shipyard in Altenrhein on Lake Constance. His work was not funded by the defence ministry, but the transport ministry, and just like that, Dornier could start building planes again. In 1918, the Dornier works had built the Zeppelin-Linday Rs IV, which was also a seaplane, but it never saw any combat because the war ended too soon for it to reach the front lines.

Soon after the Dornier Do J Wal (otherwise known as “the whale”) was built. This had a lot of hallmarks of the DO X, such as the push-pull engines and the sponsons, and it proved to be a pretty long-lasting and reliable design. But Dornier, now unshackled by the war and the treaty, wanted to go bigger.

The first designs for the DO X were put to paper in 1924, and by 1929, and after almost a quarter of a million-man hours, it was ready for its first test flight. And it worked. Granted, it didn’t fly very high or for very long, but it worked. Not just content with being the biggest plane ever at the time however, on its 70th test flight in October of 1929, it set a new world record for the number of passengers carried on a single flight with over 150, a record that would stand for the next two decades.

After a take-off run of 50 seconds, the DO X was able to climb to around 200 metres. For reference, that is low enough to crash into the Eiffel Tower about two thirds of the way up. The passengers inside the DO X were asked to crowd together on each side to help make turns.

It had completed 103 flights by 1930 and after this proof of concept, the Dornier DO X would get a few upgrades. The inside of the plane would be redesigned to be the more luxurious layout for passengers that we know. And rather than 150, it would sit fewer passengers in greater comfort. Generally, for short-haul flights around 100 people would be seated, but for longer-haul ones it would only be around 66.

Crucially, the next major modification was for the engines. The DO X was refitted with 610 horsepower Curtiss “Conqueror” water-cooled V-12s, which allowed it to reach a practically dizzying altitude of 500 metres. And this height made it possible for the DO X to be officially capable of crossing the Atlantic.

The DO X was a technical and engineering marvel, so it would be sent all over the place on a tour to showcase the might of German engineering, but there was a slight issue. Whilst the DO X had been designed with transatlantic travel in mind, the new engines were gas guzzlers, which made the trip across the Atlantic difficult.

In 1930 the DO X left Switzerland where it was built, flew to the Netherlands, the UK, France and Spain before landing in Portugal, where another mishap occurred when a fire consumed most of one of the wings. Repairs took weeks. It then hopped down the West Coast of Africa, reaching the Cape Verde Islands and finally setting off towards the new world, landing in Brazil.

It then turned North, reaching New York in August of 1931, where it was hoped that the flying ship, which caused a sensation everywhere it went, would attract rich American buyers for the company. But at this point, the Great Depression had just hit the USA two years prior in 1929, and nobody really had any money to spare on extravagant luxury planes like the DO X. So, whilst causing a stir across Europe and the Americas, the transatlantic venture would ultimately be a failure.

At least it would only take three days to do the return trip, rather than the months it took to get there. But even this in itself was an achievement. Charles Lindbergh had only flown across the Atlantic solo in 1927, five years prior.

Now this behemoth was doing it with scores of passengers in relative luxury.

Dornier had put a lot into the venture, but he was unable to fund more flights for the DO X so the original was turned over to the German flag-carrying airline, Lufthansa. Its next major tour was supposed to see it fly to Vienna, Budapest, and Istanbul in 1933, but it only reached the reservoir city of Passau in Bavaria after the tail of the boat was torn off during a botched landing on a lake. This effectively killed any market the DO X could have had in Europe.

Lufthansa had no interest in maintaining an aircraft so large and so complicated. After it was repaired, it was transported to the Berlin Museum of Technology where it was permanently shelved.

That didn’t mean no other DO X planes existed though. The DO X2 and X3 were sold to Italy in 1931 with the intention of them being used as luxury passenger planes, but for whatever reason, this never happened. So instead, they were given to the Italian military to see if they could do anything with them. However, the Italian engines that they used were even less powerful than the original ones Dornier designed, which severely limited the already lumbering craft to little more than long range maritime patrol planes.

And that’s the unsatisfying end of it. The DO X2 and X3 were eventually scrapped by the Italian navy by 1937. Europe was on a war footing, and in Italy no material could be spared. In Nazi Germany, the DO X1 remained in the Berlin Museum of Technology during the war. Then during an allied air raid in late November of 1943, the museum was bombed and the original DO X was destroyed. Along with the machines, most of the construction plans were also lost along the way.

Dornier himself died in 1969, having built many incredible machines, some for good, some for evil. But it would appear that his most ambitious and marvellous creation of all would go to the grave with him.

Or would it?

The DO X Reborn

This incredible aircraft has garnered quite a few fans over the years. From its sheer scale, to its slightly ridiculous look, to the impressive mix of maritime and air design. There are a select number of people who are trying to bring the Dornier DO X back from the dead.

The leader of such an effort is Peter Kielhorn, a former Dornier employee. After the DO X, Dornier the company lived on, as it was a successful element of the German war machine. Post war it continued as a private company to great success, building jets, military aircraft, spacecraft and yes, even still making seaplanes.

After Kielhorn retired, he was looking for something to do, quoting: “After finishing my book, I looked for my next challenge of what to do, and I decided to write about the DO X or the construction of the DO X, and this was in 2013 / 2014.”

The DO X fascinated Kielhorn, and soon he met like-minded individuals who were also transfixed by the flying ship. But not content with it simply being an interesting engineering footnote lost to history, Kielhorn and several others conspired to rebuild an original DO X1 replica.

Kielhorn didn’t know how to rebuild an aircraft whose plans had almost all been lost decades before, but where there’s a will, there’s a way. He approached the University of Friedrichshafen in 2014, the same Friedrichshafen where the original Dornier company was founded almost a century before, to see if they could help. In 2018 the Universities of Lörrach and Mosbach joined in the effort. Slowly, The Friends and Support Association DO X, a volunteer organisation, formed around the project to get it built.

But this would not be an easy task.

There were very few surviving plans of the DO X left. And before any parts could be cut, a digital replica of the plane would need to be designed to the right specifications. That’s where the universities come in.

With a swathe of young minds, computer-aided-design software and final projects needed to be completed for course credits, the students built a digital version of the DO X with the volunteer’s added specifications. And this was all based on drawings of three sides of the DO X, interior views of the flying ship, as well as high-resolution images of fuselage frames and structural components taken during the building phase of the original.

The Flight Museum of Altenrhein even had an original DO X propellor that the team could scan with lasers to reverse engineer it. Overall, the Universities and their students contributed 96,000-man hours to create the digital data needed for the project. The final stage before parts get cut and built en masse is in the detailed design of the structural components, which is still ongoing, but thanks to some source materials from Dornier, progress is being made. By August of 2021, 54 ribs of the original fuselage had been designed in detail, meaning that the complete fuselage of the ship at that time was nearly ready for rebuilding.

Plans for the next stages is to put the plane together as it is designed like a big LEGO set in Switzerland. A large facility which can accommodate the constructed nearby to Lake Constance makes the chances of the DO X seeing the water again a reality. As of January 2024, Peter Kielhorn estimated that roughly two percent of the replica had been constructed. The plan is for the digital DO X to be completed by 2026, with the fully realised and reconstructed replica to be built in time for the 100th anniversary of the DO X’s first test flight: July 12th, 2029.

But here’s the crucial question: will it fly?

Sorry to disappoint, but no, the replica as far as we know will not be able to fly. But it will be fully buoyant, built at full scale and it will even be able to taxi on the water using electric power. The team have even redesigned the Curtiss V12 engines thanks to Wright State University in Dayton, Ohio, who were able to provide a manual of the original. So, almost a century after the last remnants of the Dornier DO X were seemingly destroyed forever, soon it may be brought back from the brink of extinction for humanity to witness in awe all over again.

And the flying boat is already gaining more popularity and traction in the mainstream again. You can buy and fly the plane yourself on Microsoft Flight Simulator, if that’s your thing. But if you wait just a little longer, come 2029 you should be able to go and see the real thing yourself.

Whilst the Dornier DO X was never a commercial success, it was still emblematic of the times it was built. Full of ambition, promise and striving for new ways to do old things. And whilst it wasn’t the prettiest, or the easiest to fly, or the most efficient, the fact that it existed at all is something to be celebrated. It was a marvel of its time, demonstrating not only the force of nature that air power would soon become, but also showing that daring to dream moves us all forward a little at a time.

A quote from the Friends of the DO X’s website probably puts it, and probably Dornier’s own thoughts best: “You just have to want it – then it will succeed.”

Key Takeaways

• The Dornier DO X was a massive flying boat built in the late 1920s, combining air and sea travel.
• It featured 12 engines in a push-pull configuration and had a luxurious interior modeled after cruise liners.
• Despite its innovative design, the DO X faced practical issues like engine overheating and low altitude.
• Only three DO X models were built, with the first used for promotional tours and the others by the Italian navy.
• Efforts are underway to rebuild the DO X, with a full-scale replica planned for completion by 2029.

Sources

• Original MegaProjects video: Dornier Do X: The Largest, Heaviest, and Worst Flying Boat
• Hero image source by Wusel007 / openverse, by-sa.

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