How the US Navy Turned Coral Reefs into ‘Concrete Carriers,’ Bringing the B-29 Superfortress Straight to Japan

The air inside Petty Officer First Class Nakamura Kenji’s Mitsubishi J2M Raiden was cold enough to crack bone. On November 24, 1944, at 31,000 feet above Tokyo, frost spidered across the cockpit glass. Kenji shoved his gloved hands against the control column, his engine coughing in the thin, oxygen-starved atmosphere.

Outside, the sky was a hard, metallic blue, sliced by thick white contrails that did not belong to the Imperial Japanese Air Force. Ahead of him, like a slow-moving silver city in the clouds, flew a formation of giants. They were shimmering, four-engined monsters—the B-29 Superfortress.

Nakamura had heard the rumors of a bomber that flew higher and faster than any fighter, but he had believed the briefings: Japan was a fortress protected by the vastness of the Pacific. These bombers were coming from the east, from the open ocean, where every map insisted there was nothing but water and tiny, primitive coral specks.

But the maps were wrong. Somewhere out there, the Americans had done the impossible. They had turned the ocean into a highway.

I. The Island Eaters: The Seabees’ Miracle

While Nakamura struggled to reach the “untouchable” silver ghosts over Tokyo, 1,500 miles to the south, the answer was vibrating through the very earth of a small island called Tinian.

Barely twelve miles long and flat as a tabletop, Tinian had once been a quiet patch of sugarcane. Now, it was a cacophony of industrial violence. Under a sun that turned the air into a white haze, the US Navy Seabees (Construction Battalions) were performing a feat of engineering that defied Japanese military doctrine.

The challenge was immense. A fully loaded B-29 weighed over 120,000 lbs ($54,000\text{ kg}$). Standard dirt or grass strips would liquefy under that pressure. To solve this, the Seabees turned to the island’s own skeleton: Coral.

They blasted the reefs and hollowed out the hills. They dumped millions of tons of crushed coral into yawning trenches. When wetted with salt water and compacted by ten-ton rollers, the coral underwent a chemical reaction, binding together into a surface as hard as granite.

By October 1944, Tinian’s North Field had become the largest airport in the world. Four parallel runways, each nearly 8,500 feet ($2,600\text{ m}$) long, ran across the plateau. From the air, the island no longer looked like land; it looked like a massive, printed circuit board etched with straight lines and symmetrical taxiways.

II. The Concrete Noose Tightens

In the operations room of the Japanese 10th Air Division, staff officers stared at their grease-pencil plots in disbelief. “It’s impossible,” one muttered. “They don’t have the fuel to fly from Hawaii, and China is too far. Where are they launching from?”

The realization that the Americans had turned the Mariana Islands—Saipan, Guam, and Tinian—into “unsinkable aircraft carriers” was a psychological blow as heavy as any bomb. Japan had built its defense on the idea of a “Decentralized Air Defense,” believing the Pacific’s distances would protect their industrial heartland.

But the Seabees had folded the Pacific in on itself. By building these coral islands, they brought Tokyo, Nagoya, and Osaka within a 14-hour round trip. The B-29s didn’t just fly; they loitered. They flew with full bomb bays and fuel to spare.

III. The Fire Below, The Coral Above

By March 1945, the strategy changed. Major General Curtis LeMay realized that the high-altitude jet stream was scattering his bombs. He ordered the B-29s to go low—at night.

On Tinian and Saipan, the mission profile shifted. The bomb loads became incendiary clusters—M-69 canisters designed to ignite the wooden architecture of Japan. On the flight lines, ground crews worked in a frenzy. The runways, already hammered by the weight of the silver giants, began to show ruts. The Seabees lived on the strips, patching holes with fresh coral and hot asphalt even as the engines of the next wave began to roar.

Over Tokyo, Nakamura Kenji saw the result. The city was no longer a collection of targets; it was an ocean of flame. The B-29s were now attacking with a “swagger”—a terrifying confidence. Nakamura realized that even if he shot one down, the Americans would just roll another one off a cargo ship onto a coral hardstand a thousand miles away.

IV. Salvation and Destruction: Iwo Jima

As the campaign intensified, geography betrayed the Japanese one more time. Between the coral islands and Tokyo sat a black, volcanic tooth: Iwo Jima.

Japanese planners had intended Iwo Jima to be a shield, a base for fighters to intercept the B-29s. But once the US Marines took the island after a brutal 36-day battle, it transformed into a safety net.

Over 2,200 B-29s would eventually make emergency landings on Iwo Jima’s sulfurous soil. Bombers that were shot up, low on fuel, or failing mechanically no longer vanished into the Pacific. They landed, repaired, and flew again. For Nakamura, this was the ultimate defeat. The Americans had not only built a highway of coral; they had built a service station halfway home.

V. The Shadow of Enola Gay

August 6, 1945. 2:00 a.m. North Field, Tinian.

The island was a ghostly plane of white light and shadow. At the end of Runway A, a B-29 named Enola Gay taxied into position. Its four R-3350 engines roared with a synchronized growl that vibrated through the coral bedrock.

Colonel Paul Tibbets pushed the throttles forward. The aircraft thundered down the coral ribbon, the weight of the “Little Boy” atomic bomb pressing the tires hard against the concrete-sealed surface. As the island fell away beneath the wings, the sugarcane fields of Tinian launched a mission that would end the war and change human history forever.

Conclusion: The Highway to Surrender

When the surrender was announced by the Emperor’s voice on August 15, Nakamura Kenji sat in his barracks, staring at a map of the Pacific. He finally saw the photographs of the Mariana airfields. He saw the four parallel runways of Tinian stretching like a giant’s ribs across the earth.

He understood then that the war hadn’t been lost in the sky. It had been lost in the soil. The Americans had treated geography not as a barrier, but as a raw material. They had reshaped islands into machines.

The Pacific was no longer a moat; it was a highway paved in concrete and coral. And on that highway, the B-29 Superfortress had driven straight into the heart of an empire.