The Defeat of Japan and the Development of the Atomic Bomb

The United States entered World War II following the Japanese attack on Pearl Harbor, requiring a period of time to rebuild the US Navy.
Unlike the European theater, which featured a coalition including the British, Soviet Union, reorganized French forces, and Canadian soldiers, the Pacific theater was primary a conflict between the United States and Japan.
The military effort in the Pacific was largely conducted by the US Navy and the US Marine Corps.
The Marine Corps serves as the landing force for the Navy, operating under the Navy's umbrella to put personnel on the ground after naval engagement.

By the start of the war, Japan controlled a significant portion of the region.
In the $1930s$ , Japan invaded Manchuria and later China.
Some historians suggest that World War II may have effectively begun with these Japanese invasions, which predated the expansionist movements of Adolf Hitler.
Japan eventually expanded into Southeast Asia.

At the height of their power, the Japanese occupied territories including the Philippines, which the US had possessed since the Spanish-American War.
The US evacuated the Philippines in the face of growing Japanese power, leading to a Japanese occupation for the duration of the war until American forces eventually retook it.
The US military strategy was known as "island hopping."
The goal was to gain footholds closer to the Japanese home islands to eventually force a surrender.
A specific objective was to capture islands with terrain large enough to support aircraft landing strips, which would facilitate a long-range bombing campaign against Japan.

US forces encountered a Japanese military culture where surrender was not recognized.
Surrender was considered a source of deep shame; according to Japanese warrior culture, an individual who surrendered would be obligated to perform ritual suicide.
This resulted in an enemy that would continue fighting even when outnumbered by ratios such as $5,000:1$ .
American military planners feared that an invasion of the Japanese home islands would involve combat against the entire population, including women and children.
Estimates for a land invasion of Japan suggested a potential loss of $1,000,000$ US soldiers.
To provide context, total US casualties for the entire war (both Europe and the Pacific) were less than $400,000$ . An additional $1,000,000$ deaths was considered a prohibitive cost.

The Manhattan Project was the top-secret research initiative dedicated to developing atomic weapons.
Despite the name, the work did not take place in Manhattan; it was distributed across various sites including Tennessee, New Mexico, Washington, Illinois, and Ohio.
Each facility worked on isolated components of the research, and only a handful of individuals understood the full scope of the results.
The project was initiated following a $1939$ letter from Albert Einstein to President Franklin D. Roosevelt (FDR).
Einstein, a Jewish theoretical physicist who had fled Hitler's rise in Germany, warned FDR that his colleagues remaining in Germany were attempting to split the atom to create a weapon.
Einstein argued that if Hitler acquired such a weapon first, the fight against fascism would be lost.
The US subsequently invested billions of dollars into the project over several years.

Although the traditional rules of war discouraged targeting civilian populations, these norms were abandoned by both sides during World War II.
Precedents included the German bombing of London and the Allied bombing of industrial cities to destroy urban centers.
Prior to using atomic weapons, the US conducted a bombing campaign against Japanese cities like Tokyo using incendiary weapons (firebombs).
Japanese architecture, largely comprised of wood and paper, was highly susceptible to fire, making firebombing extremely destructive.

Harry Truman became FDR's Vice President during FDR's fourth term.
Truman was so far removed from the inner circle that he did not learn about the Manhattan Project until FDR died and he was sworn into office.
Truman was briefed on the project approximately two weeks after taking the oath of office.
In July $1945$ , the first atomic test was conducted in the New Mexico desert.
Truman's diary recorded the following observations from the test: - The explosive utilized only $13\,\text{pounds}$ of material. - It caused the complete disintegration of a $60\,\text{foot}$ steel tower. - It created a crater $6\,\text{feet}$ deep and $1,200\,\text{feet}$ in diameter (roughly the length of four to eight football fields). - It knocked over a steel tower located a half-mile away. - It knocked men down at a distance of $10,000\,\text{yards}$ (nearly $5\,\text{miles}$ ). - The explosion was visible from $200\,\text{miles}$ away and audible from $40\,\text{miles}$ away. - Due to the curvature of the earth (horizon is roughly $11\,\text{miles}$ away), the explosion cloud had to be exceptionally tall to be visible at $200\,\text{miles}$ .

Once capacity was confirmed, Truman authorized the military to use the weapon between July and August 10th.
Truman participated in selecting the targets: Hiroshima and Nagasaki.
Hiroshima: Bomb dropped on August 6th. This target was selected partly due to the presence of a naval base.
Nagasaki: Bomb dropped on August 9th. This was a civilian population center. It was chosen partly because it is surrounded by mountains; scientists wanted to observe the "echo effect," where the concussion blast reflects off the terrain to maximize destruction.
Both cities were selected because they had not yet been damaged by conventional bombing, allowing the US to accurately assess the power of the atomic bomb.
Japan surrendered unconditionally on August 12th.

Question: Does Japan have any military today or is it still like that?
Response: Under the terms of the peace treaty, Japan agreed to never maintain a traditional military capable of projecting power beyond its borders. They maintain a Self-Defense Force, but the United States remains obligated to serve as their primary defense. US sailors and soldiers are frequently stationed in or around Japan for this reason. Today, Japan is a critical ally and an important international trading partner for the US.

The class is tasked with analyzing sources regarding the decision to use the bomb, including: - Harry Truman: Memoirs (autobiographical reflections written for the general public). - Admiral Leahy: Chief of Staff memoirs. Leahy was the first modern Chief of Staff, a primary advisor who controlled the President's calendar and managed White House personnel. - Secretary of War: A civilian position (non-uniformed) appointed by the President to lead the War Department, overseeing the Army and Air Force.