They Bought America’s “Failed” Airliner in Crates, Faked Its Death in Tokyo Bay, and Tried to Turn It Into a Pacific Super-Weapon—How Japan’s $950,000 Gamble Became One of the Most Spectacular Heavy Bomber Flops of World War II

Part 1: The Airliner That Was Supposed to Change Everything

April 8, 1941. Humid air outside Tokyo. A runway shimmering in the afternoon heat.

At 2:35 p.m., a four-engine giant lumbered forward at Nakajima’s test field. It was long—over a hundred feet nose to tail. Wide—nearly 140 feet across the wings. And loud. The kind of loud that vibrates in your sternum.

Imperial Japanese Navy officers stood stiffly near the tarmac, their caps pulled low. Engineers clustered behind them. Eighteen months of work. A small fortune spent. And underneath all of it, a secret.

The airplane clawed into the sky.

Too slowly.

The engines strained. The controls felt heavy—sticky, like the air itself didn’t want to cooperate.

Something was wrong.

Truth be told, something had been wrong from the beginning.

But to understand how Japan ended up flying this unwieldy brute—what would become the Nakajima G5N—you have to rewind a few years and cross the Pacific. Because this story doesn’t start with war. It starts with ambition. American ambition.

Back in 1935, commercial aviation in the United States was having its golden-hour glow. Airlines were expanding. Passengers were (slowly) getting over the idea that flying meant flirting with gravity’s bad side. And manufacturers were in a quiet arms race to build something bigger, faster, more comfortable.

The Douglas Aircraft Company had already rolled out the legendary Douglas DC-3, an airplane so successful it practically defined its era. But even before the DC-3 was fully entrenched, airline executives were dreaming bigger.

William Patterson of United Airlines walked into Douglas with a wild idea: a four-engine airliner that could cross the entire United States without stopping for fuel. Forty-two passengers by day. Thirty in sleeper berths by night. Pressurized cabins. Air conditioning. Luxury in the sky.

It sounded a bit like science fiction in 1935.

Douglas hesitated. Four engines? For passengers? No airline had done that with a landplane. The technology existed—but barely. The risks were enormous.

Still, other carriers joined the party. American. Eastern. Pan Am. Transcontinental and Western Air (the future TWA). Each kicked in $100,000—half a million dollars pooled for development. Real money in Depression-era America.

And so began the project that would become the Douglas DC-4E.

Two years. Eight thousand drawings. Over a thousand hours of wind tunnel tests. 1.3 million rivets. Half a million man-hours.

What emerged in 1938 looked like it had landed from the future.

 

It sat level on the ground thanks to tricycle landing gear—nose wheel up front instead of a tail-down stance. That seems normal today. Back then? Revolutionary.

The wing spanned 138 feet. Four Pratt & Whitney Twin Hornet engines hung from it. And the tail—this is important—had three vertical fins. Not because it looked cool. Because a single tall tail wouldn’t fit in existing airport hangars. Airlines didn’t want to build new ones.

Engineering is compromise. Always.

Inside, the cabin felt almost decadent for the era. Proper chairs. Space to move. Sleeper berths for overnight transcontinental trips. The idea that you could eat dinner in New York and wake up in Los Angeles in a real bed felt borderline miraculous.

On June 7, 1938, test pilot Carl Cover took the DC-4E into the sky over Santa Monica.

It flew.

It handled… reasonably well.

That word—reasonably—would come back to haunt them.

One of the most poetic moments in aviation history happened the following year. In June 1939, the DC-4E landed in Dayton, Ohio. A special passenger boarded for a short demonstration flight: Orville Wright.

Thirty-six years earlier, Orville and his brother had flown 120 feet in 12 seconds at Kitty Hawk.

Now he sat inside a four-engine airliner capable of crossing a continent.

You could almost feel history folding in on itself.

But romance doesn’t pay fuel bills.

When United Airlines evaluated the DC-4E in real-world operations, the cracks widened fast.

It was too complex. Too heavy. Too thirsty.

Maintenance crews trained on DC-3s stared at its electrical systems like they’d opened the hood of a spaceship. Fuel consumption was worse than predicted. Performance sagged when seating increased to improve economics. Weight ballooned from 50,000 pounds to 65,000 pounds.

Every fix added weight.

Every added pound demanded more power.

The engines strained.

Sound familiar?

By mid-1939, airline after airline backed away. The DC-4E—this technological marvel—was simply too much airplane for the market.

Douglas had spent roughly $3 million.

And they were stuck with a white elephant.

Here’s where the story twists.

In late 1939, representatives from Japan—through Mitsui Trading Company and the civilian airline Dai Nippon Koku—approached Douglas. They wanted to buy the prototype.

Price: $950,000.

Douglas didn’t ask too many questions. Why would they? Selling commercial aircraft abroad wasn’t unusual. Export controls were light.

So on September 29, 1939, the DC-4E was disassembled in California, packed into crates, and shipped across the Pacific. Along with it went the full treasure chest: engineering drawings, specifications, test data, even the wind tunnel model.

Douglas technicians traveled to Japan to help reassemble it.

They thought they were assisting a customer.

They were, in fact, tutoring a future adversary.

Because Dai Nippon Koku wasn’t the real buyer.

The real buyer was the Imperial Japanese Navy.

Part 2: The Fake Crash and the Deep Mountain

Once reassembled at Haneda Airport near Tokyo, the DC-4E wore a gleaming emerald and silver livery. Photographers snapped pictures. Executives smiled for the press.

And then—almost as soon as the spotlight faded—the airplane disappeared.

Officially, it crashed into Tokyo Bay.

Unrecoverable.

Case closed.

Except it hadn’t crashed.

It had been quietly transferred to Nakajima Aircraft Company and rolled into a hangar for dissection.

The “crash” story solved several problems at once. It hid the aircraft from American scrutiny. It explained its absence from airline service. And it shielded the Navy’s secret bomber program.

Inside that hangar, engineers measured everything. Weighed components. Traced wiring. Studied structural joints. The DC-4E was reverse engineered bolt by bolt.

What emerged from that effort was the Nakajima G5N, nicknamed Shinzan—“Deep Mountain.”

At a glance, the resemblance to the DC-4E was obvious. The wing geometry was nearly identical. The tricycle landing gear remained. Overall proportions echoed the American original.

But the fuselage was militarized.

Gone were passenger seats and sleeper berths. In their place: a long bomb bay capable of carrying up to 4,000 kilograms of bombs—or torpedoes for anti-shipping missions. The nose was glazed for a bombardier. Defensive guns sprouted from dorsal and tail turrets.

The triple tail was replaced by a twin-fin arrangement.

And then came the engines.

Instead of copying the American Pratt & Whitney design, Nakajima installed its own NK7A Mamori radial engines. On paper, they were monsters—1,870 horsepower each. More than the DC-4E’s 1,450 horsepower engines.

The logic seemed airtight: more power equals better performance.

Except paper horsepower isn’t the same as delivered horsepower.

When the first prototype took off on April 8, 1941, optimism hung in the air.

It evaporated quickly.

The Mamori engines rarely achieved their rated output. They ran rough. They overheated during climbs. Reliability was poor. To prevent catastrophic failures, engineers had to detune them—reducing power and making an already heavy airplane even more underpowered.

Performance numbers told a grim story.

Maximum speed: about 261 mph.

Service ceiling: under 25,000 feet.

Range: roughly 2,600 miles—short of the 3,000-nautical-mile requirement.

It was slower than contemporary Allied heavy bombers like the Boeing B-17 Flying Fortress. It carried less. It climbed worse.

Japan had wanted a strategic bomber capable of projecting power across the Pacific—perhaps even striking Hawaii or beyond.

Instead, they had a lumbering, overweight aircraft straining against physics.

Engine swaps were attempted. Later prototypes used Mitsubishi Kasei engines—more reliable, but less powerful. Performance deteriorated further.

Six prototypes were built.

None met requirements.

The program quietly died as a bomber.

The Imperial Japanese Army briefly considered its own versions (Ki-68, Ki-85) but watched the Navy’s struggles and backed away. Even in wartime, pragmatism sometimes wins.

Part 3: The Bomber That Became a Cargo Hauler—and the Lesson No One Wanted

What do you do with a failed heavy bomber in the middle of a global war?

You improvise.

Four of the six G5Ns were converted into long-range transports. Bomb bays removed. Guns reduced. Crew shrunk. They were redesignated G5N2L.

They hauled cargo across Japan’s empire—Hong Kong, Formosa, the Philippines, the Mariana Islands.

The “Deep Mountain” that was supposed to cast a shadow over the Pacific became a glorified freight truck.

Meanwhile, Allied intelligence spotted the large four-engine aircraft in reconnaissance photos. Analysts assigned it the code name “Liz,” assuming it was a strategic threat.

It wasn’t.

It was a paper tiger hauling spare parts.

The irony is almost painful.

Back in America, Douglas absorbed the failure of the DC-4E and went back to the drawing board. They simplified. They shed weight. They abandoned the over-ambitious systems.

The result was a redesigned DC-4, militarized as the Douglas C-54 Skymaster.

Over 1,200 were built during the war. They carried troops and cargo across oceans. After the war, they sustained the Berlin Airlift. They flew for airlines worldwide for decades.

Douglas learned from its mistake.

Nakajima copied the mistake.

That difference—understanding versus imitation—made all the difference in the world.

By war’s end, none of the G5Ns survived. They were destroyed, scrapped, cannibalized, or lost in the chaos of 1945. The original DC-4E prototype had long since been stripped for parts.

The $950,000 gamble had yielded six prototypes and zero operational bombers.

You can’t ship institutional memory in a crate.

You can’t reverse engineer context.

Japan had bought America’s rejected airliner hoping to leapfrog years of development. Instead, they inherited its weaknesses—and added new ones.

The “Deep Mountain” never cast its shadow.

And somewhere in the long arc of aviation history, that lesson still echoes:

Copying technology isn’t the same as understanding it.