History's deadliest air raid happened in Tokyo during World War II and you've probably never heard of it

Tokyo (CNN)Everywhere she turned, 8-year-old Haruyo Nihei saw flames.

Bombs dropped by the Americans had created tornadoes of fire so intense that they were sucking mattresses from homes and hurling them down the street along with furniture -- and people.
"The flames consumed them, turning them into balls of fire," says Nihei, now 83.
    Nihei had been asleep when the bombs began raining down on Tokyo, then a city comprised of mostly wooden houses, prompting her to flee the home she shared with her parents, her older brother and her younger sister.
    As she raced down her street, the superheated winds set her fireproof wrap ablaze. She briefly let go of her father's hand to toss it off. At that moment, he was swept away into the crush of people trying to escape.
    As the flames closed in, Nihei found herself at a Tokyo crossroad, screaming for her father. A stranger wrapped himself around her to protect her from the flames. As more people piled into the intersection, she was pushed to the ground.
    As she drifted in and out of consciousness beneath the crush, she remembers hearing muffled voices above: "We are Japanese. We must live. We must live." Eventually, the voices became weaker. Until silence.
    When Nihei was finally pulled out from the pile of people, she saw their bodies charred black. The stranger who had protected her was her father. After falling to the ground, they'd both been shielded from the fire by the charred corpses that were now at their ankles.
    It was the early morning of March 10, 1945, and Nihei had just survived the deadliest bombing raid in human history.
    Japanese government photo shows buildings aflame after World War II firebomb raid.
    As many as 100,000 Japanese people were killed and another million injured, most of them civilians, when more than 300 American B-29 bombers dropped 1,500 tons of firebombs on the Japanese capital that night.
    The inferno the bombs created reduced an area of 15.8 square miles to ash. And, by some estimates, a million people were left homeless.
    The human toll that night exceeded that of the atomic bombings of Hiroshima and Nagasaki later that year, where the initial blasts killed about 70,000 people and 46,000 people respectively, according to the US Department of Energy.
    But despite the sheer destruction of the Tokyo air raids, unlike for Hiroshima or Nagasaki, there is no publicly funded museum in Japan's capital today to officially commemorate March 10. And while the Allied bombing of Dresden in Germany in February 1945 roused a strong public debate on the tactic of unleashing fire on civilian populations, on its 75th anniversary the impact and legacy of the Japan air raids remain largely unknown.
    An aerial view of Tokyo after it was razed by American fire bombing carried out on March 10, 1945.

    The introduction of B-29s

    The horrors Nihei saw that night were the result of Operation Meetinghouse, the deadliest of a series of firebombing air raids on Tokyo by the United States Army Air Forces, between February and May 1945.
    They were designed largely by Gen. Curtis LeMay, commander of the US bombers in the Pacific. LeMay later launched airstrikes on North Korea and Vietnam and supported the idea of a preemptive nuclear attack against Russia during the Cuban Missile Crisis in October 1962.
    Though US President Franklin Roosevelt had sent messages to all warring governments urging them to refrain from the "inhuman barbarism" of bombing civilian populations at the outbreak of war in Europe in 1939, by 1945 that policy had changed.
    After the Japanese attack on Pearl Harbor on December 7, 1941, the US was determined to retaliate. By 1942, Japan's empire in the Pacific was at its most powerful. US war planners came up with a target list designed to obliterate anything that might help Tokyo, from aircraft bases to ball bearing factories.
    But to execute its plan, the US needed air bases in range of Japan's main islands.
    With the invasion of the South Pacific island of Guadalcanal in August 1942, it began to acquire land for that purpose, continuing that mission by picking up the islands of Saipan, Tinian and Guam in 1944.
    With that hattrick in hand, the US had territories on which to build airfields for its new, state-of-the-art heavy bomber, the B-29.
    Originally conceived to strike Nazi Germany from continental US in the event Britain fell to Hitler's forces, the B-29 -- with its ability to fly fast and high and with large bomb loads -- was ideal for taking war to the Japanese homeland, according to Jeremy Kinney, curator at the Smithsonian National Air and Space Museum in Virginia.
    US B-29 bombers in flight.
    The bombers were the culmination of 20 years of aviation advances leading up to World War II and were the first to have pressurized, heated fuselages, enabling them to operate above 18,000 feet without crews having to don special gear or use oxygen masks.
    That put them out of range of most anti-aircraft guns and gave them plenty of time before fighters could rise up to engage them, Kinney said.
    "The B-29 Superfortress was the most advanced technology of its time," he said.
    And US war planners were ready to unleash it on Japan.
    But the B-29s' early attacks on Japan were considered failures.
    The planes dropped their explosive loads from the high altitudes -- around 30,000 feet -- they were designed to operate at, but as few as 20% hit their targets. US crews blamed poor visibility in bad weather and said the strong winds of the jet stream often pushed bombs off target as they fell.
    LeMay was tasked with finding a way to get results.
    His answer was so drastic it even shocked the crews who would carry out the raids.
    The B-29s would go in low -- at 5,000 to 8,000 feet. They'd go in at night. And they would go in single file, rather than in the large multi-layered formations the US had used in the daylight bombing of German forces in Europe;
    Smoke and fire rise from Tokyo during the US firebomb raid.
    Perhaps most significantly, they'd carry fire bombs, designed to set Tokyo's largely wooden landscape ablaze. Fire bombs, or incendiary bombs, let loose flammable substances as they strike, as opposed to high-explosive bombs, which destroy with concussion and shrapnel.
    When US air crews were briefed on the mission, many of the more than 3,000 Army aviators reacted with disbelief.
    Going in single file, they'd be unable to protect each other from Japanese fighters. And LeMay had ordered the large bombers to be stripped of almost all of their defensive armaments so they could carry more of the fire bombs.
    "Most men left the briefing rooms that day convinced of two things: one, LeMay was indeed a maniac; and two, many of them would not live to see the next day," wrote James Bowman, son of a B-29 fire raid crewman, in a journal compiled from records of the units involved.

    Fire from the sky

    On the evening of March 9, 1945, on Saipan and Tinian and Guam, the B-29s began leaving their island bases for the seven-hour, 1,500-mile trip to Japan.
    Early in the morning of March 10, as the Japanese slept in their low-rise, wooden homes, the first bombers over Tokyo started five sets of marking fires, smaller strikes for the rest of the bomber force to aim it, according to B-29 pilot Robert Bigelow, who recounted the raid for the Virginia Aviation History Project.
    Between 1:30 a.m. and 3:00 a.m. the main force of American B-29s unleashed 500,000 M-69 bombs, each one clustered in groups of 38 and weighing six pounds.
    The clusters would separate during their descent and small parachutes would carry each bomblet to the ground.
    The jellied gasoline -- napalm -- inside the metal casings would ignite seconds after hitting something solid and shoot the flaming gel onto the surrounding surfaces.
    Haruyo Nihei had endured US bombing raids on Tokyo before, but when her father woke her up in the early morning darkness of March 10, he shouted that this one was different.
    They needed to get out of the house and to an underground shelter without any delay.
    Nihei remembers throwing on the clothes, shoes and emergency rucksack she kept by her pillow and rushing out the house with her mom, younger sister and elder brother. The family, who owned a spice shop, lived in the downtown Tokyo district of Kameido. They rushed passed the local fishmonger's and small grocery stores that lined the streets.
    In those early moments, she remembers not so much the fire, as the air being sucked into the inferno to fuel it. The fire hadn't reached their district yet.