It was 75 years ago on August 6, 1945 when an atomic bomb was used for the first time in war. It was dropped from the B-29 bomber Enola Gay on the Japanese city of Hiroshima. The bomb, codenamed Little Boy, was used against the Empire of Japan just three weeks after the first nuclear detonation was conducted at the Trinity test site in New Mexico. 

A second atomic bomb, an implosion-type nuclear weapon codenamed Fat Man, was detonated over the Japanese city of Nagasaki on August 9. The nuclear age had arrived, and World War II had become the first – and hopefully last – “nuclear war.”

The Atomic Bomb Was A Vast Undertaking

Little Boy was anything but little in terms of devastation. It weighed just 9,700 pounds, but it had a blast yield that equaled 15 kilotons of TNT. When it was used against Hiroshima, an estimated 66,000 people were killed as a direct result of the blast and 69,000 were injured to varying degrees. 

The effort to develop the atomic bomb was also anything but small. 

While the Manhattan Project – originally designated the Manhattan District – began modestly in 1939, it eventually grew to employ more than 130,000 people, and it cost nearly $2 billion (equivalent to nearly $25 billion today). More than 90% of the cost was for building the factories and producing the fissile material. Less than 10% went to development or even production of the weapons.

What is especially astonishing about the Manhattan Project is that the research and production took place at more than 30 sites across the United States, the United Kingdom, and Canada. This included facilities in New Mexico, Chicago and Oak Ridge, Tennessee, and yet few outside the program knew exactly what was being developed.

Ultimate Classified Work: BUilding the Atomic Bomb

Secrecy was highly important and mostly effective. 

“Los Alamos was not on any map; those who moved here could not tell friends or family where they were going or what they were working on,” said Elizabeth Martineau, executive director of the Los Alamos Historical Society.

“Code names were given to well-known scientists, and code words assigned to lab work,” Martineau told ClearanceJobs. “Niels Bohr was known as Nick Baker and Enrico Fermi was known as Henry Farmer. Military Police monitored phone calls and censored mail.”

In addition, all Manhattan Project personnel information was compartmentalized on a need-to-know basis. 

“No one was allowed to discuss their work even with their families, putting strain on relationships,” added Martineau. “Manhattan Project security hid the program from the American public and even from all but a select few government officials.”

Security was tight but not leak-proof it turned out.

“At least four known spies at Los Alamos, acting independently of each other, passed secrets to the Soviet Union,” said Martineau. “Their espionage was not discovered until after the war.”

Inter Service Cooperation

Unlike perhaps any program before, the Manhattan Project depended on every branch of the service. It was U.S. Army personnel who were responsible for guarding the facilities in the United States, but it was the U.S. Navy and U.S. Marine Corps that were responsible for the safe delivery and protection of the components of the Little Boy bomb to Tinian Island in July and August of 1945.

“Military inter-service cooperation was critical in enabling the first atomic missions,” said National Museum of the U.S. Air Force historian and curator, Dr. Doug Lantry.

“Complementing the massive civilian scientific effort to create the weapons, military logistics made their delivery to Tinian Island possible,” Lantry told ClearanceJobs. “The Army and Navy worked together to transport the bombs in parts from the U.S. to Tinian for assembly. Some parts went from New Mexico to California by road convoy and others by air, and then parts went by Navy ship and Army Air Forces aircraft across the Pacific.”

Actual Radio Silence for Atomic Bomb Delivery

Many of the components for the Little Boybomb left San Francisco on the cruiser USS Indianapolis on July 16. This was the same day as the Trinity tests. The USS Indianapolis arrived at Tinian on July 26. During that top secret voyage, the ship also carried about half the world’s supply of uranium-235 at the time. The ship was still on radio silence when it sunk on its return voyage to Leyte. 

Only 316 of the nearly 900 men set adrift after the sinking were eventually rescued. The ship’s inability to radio for help prior to sinking was part of the issue. The sailors who didn’t survive could be considered among the forgotten casualties of the Manhattan Project. 

“Secrecy was paramount because there was no great stockpile of bombs or parts,” added Lantry. “This in turn required vigilant security surrounding all the parts and their delivery.”

Flight Selection

The same level of secrecy extended to the aircrews who were charged with delivering the bomb to its final target via the U.S. Army Air Force’s B-29 bombers. The B-29 was the most advanced aircraft developed during the war. Its pressurized cabin feature allowed the B-29 to fly higher than most anti-aircraft weapons could reach at that time. 

More than a year before the mission, then Major Paul Tibbets was selected to command the 509th Composite Group. The 509th Composite Group was a fully self-contained organization of about 1,800 men. Tibbets was chosen over older officers. He had shown experience in both staff and command duties in heavy bomber combat operations. Also, he was already an experienced B-29 pilot. 

It was the newly promoted Col. Tibbets who determined who was to go on the mission. 

“509th Composite Group commander Col. Paul Tibbets, who led the August 6th mission, carefully selected the flight crew members,” said Jeff Duford, curator at the National Museum of the United States Air Force. 

“Each man was chosen for their exceptional abilities, experience, and reliability,” Duford told ClearanceJobs. “Tibbets actually chose the aircraft on the assembly line at the Martin plant in Omaha, Nebraska, in May 1945.  Shortly before the atomic mission, he named it ‘Enola Gay’ after his mother.”

Was The Atomic Bomb Necessary?

For 75 years, the same question has been asked over and over. Was it actually necessary to drop the bomb on a Japanese city? That question might continue to be asked for another millennia. However, it’s also been debated that a demonstration of the bomb would have been sufficient to end the war.

“The bomb was not necessary to end the war without an invasion, and Truman, his advisors, and the military leaders all knew this to be true,” explained Dr. Peter Kuznick, professor of history at the American University. 

“Seven of America’s eight five-star admirals and generals in 1945 are on record saying the bomb was either militarily unnecessary, morally reprehensible, or both. U.S. intelligence had been saying for months that Soviet entry into the Pacific War, which Stalin promised would take place three months after the end of the war in Europe, would itself force Japanese surrender,” Kuznick told ClearanceJobs.

“A demonstration might have been sufficient, but Byrnes opposed it when it was discussed by the Interim Committee,” Kuznick added. “Oppenheimer initially had his doubts that it would have been dramatic enough, but he changed his mind after witnessing the Trinity Test in Alamogordo on July 16. FDR often spoke of first having a demonstration before using the bomb on Japanese targets. But the U.S. chose to use the bomb in large part to send a message to the Soviet Union, with whom early Cold War tensions were emerging. Both James Byrnes and Gen. Leslie Groves, two of those who mostly greatly influenced decisions on the bomb, were explicit about this. And that is precisely how Soviet leaders responded, putting the world on a glide path to potential annihilation, as many scientists warned such use of the bomb would do.”

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Peter Suciu is a freelance writer who covers business technology and cyber security. He currently lives in Michigan and can be reached at You can follow him on Twitter: @PeterSuciu.