Overview
This lecture traces the development, deployment, and aftermath of the atomic bombs dropped on Hiroshima and Nagasaki during World War II, covering key scientific discoveries, military decisions, and lasting impacts.
Prelude to the Bombings
- The U.S. dropped atomic bombs on Hiroshima (August 6, 1945) and Nagasaki (August 9, 1945), ending WWII in the Pacific.
- Clear weather, careful mission planning, and last-minute bomb assembly were crucial for the attacks.
- Enola Gay carried "Little Boy" to Hiroshima; Bockscar delivered "Fat Man" to Nagasaki.
Scientific Discoveries and the Manhattan Project
- In 1939, Meitner and Frisch discovered uranium fission, releasing massive energy.
- U.S. scientists confirmed fission of uranium-235 and plutonium-239 could cause atomic explosions.
- The Manhattan Project, led by General Groves and J. Robert Oppenheimer, aimed to create atomic bombs.
- Chicago Pile No. 1 achieved the first self-sustaining nuclear chain reaction in 1942.
Bomb Development and Testing
- U.S. military seized land for plutonium production, displacing local populations and Native Americans.
- Los Alamos, New Mexico, was chosen as the bomb development and test site.
- On July 16, 1945, the Trinity test successfully detonated the first atomic bomb.
- The U.S. secretly prepared more bombs and decided to use them instead of invading Japan.
Hiroshima and Nagasaki Attacks
- Hiroshima bomb "Little Boy" detonated at 1,900 ft, killing ~70,000 instantly, with more dying from burns/radiation.
- Nagasaki bomb "Fat Man" was more powerful, killing ~40,000 instantly and destroying much of the city.
- Both attacks involved precise flying, last-second decisions, and extreme crew risk.
Aftermath and Surrender
- Japan offered conditional surrender after the bombings; the U.S. demanded unconditional terms.
- Japan surrendered on August 14, 1945; formal signing occurred on September 2, 1945.
- U.S. occupied Japan for seven years; many survivors suffered long-term effects from radiation.
Key Terms & Definitions
- Fission — splitting of an atom’s nucleus, releasing large amounts of energy.
- Chain reaction — process where released neutrons cause further fission, sustaining energy output.
- Manhattan Project — U.S. top-secret project to build an atomic bomb.
- Critical mass — minimum amount of fissile material needed for a chain reaction.
- Radiation poisoning — illness caused by exposure to radioactive materials.
Action Items / Next Steps
- Review bomb mechanics (fission, chain reaction) and major Manhattan Project milestones.
- Study ethical debates on atomic bomb use and its long-term consequences.
- Prepare for questions on the sequence of wartime events and key figures involved.