What was the United States strategy in World war 2?

“Leapfrogging” was the Allied strategy of bypassing and isolating fortified positions by focusing on strategically important islands.

Explain the military strategy behind Allied leapfrogging in the Pacific

Key Takeaways

Key Points

• Leapfrogging  was a military strategy that entailed bypassing and isolating heavily fortified Japanese positions while preparing to take over strategically important islands. It originated from island hopping.
• Island hopping entailed taking over an island and establishing a military base there. The base was in turn used as a launching point for the attack and takeover of another island.
• U.S. Admiral Chester Nimitz was appointed the title of “Supreme Allied Commander Pacific Ocean Areas,” and in the other major theater in the Pacific region, known as the South West Pacific theater, Allied forces were commanded by U.S. General Douglas MacArthur. Both Nimitz and MacArthur applied leapfrogging and island hopping as major strategies.
• Leapfrogging was based on both seaborne and air attacks to blockade and isolate Japanese bases, weakening their garrisons and reducing the Japanese ability to resupply and reinforce them.
• Leapfrogging would allow U.S. forces to reach Japan more quickly and not expend the time, manpower, and supplies to capture every Japanese-held island on the way. It would also give the Allies the advantage of surprise and keep the Japanese off balance.

Key Terms

• Leapfrogging: A military strategy employed by the Allies in the Pacific War against the Axis powers (most notably Japan) during World War II. It entailed bypassing and isolating heavily fortified Japanese positions while preparing to take over strategically important islands.
• Island hopping: A military strategy employed by the Allies in the Pacific War against the Axis powers (most notably Japan) during World War II. It entailed taking over an island and establishing a military base there. The base was in turn used as a launching point for the attack and takeover of another island.

Leapfrogging was a military strategy employed by the Allies in the Pacific War against the Axis powers (most notably Japan) during World War II. It entailed bypassing and isolating heavily fortified Japanese positions while preparing to take over strategically important islands. Leapfrogging originated from island hopping, a strategy with which leapfrogging is sometimes misleadingly confused. Island hopping entailed taking over an island and establishing a military base there. The base was in turn used as a launching point for the attack and takeover of another island. The result of island hopping was a chain of established bases while the result of leapfrogging was subduing certain strategically important islands while destroying military bases on other islands and thus isolating them in the process. Each of the strategies had its advantaged and was employed in the Pacific War.

Background

On December 7, 1941, after failing to resolve a dispute with the United States over Japan’s actions in China and French Indochina, the Japanese attacked the U.S. Pacific fleet at Pearl Harbor, Hawaii. The attack crippled most of the U.S. Pacific fleet’s battleships and started a formal state of war between the two nations. Attacks on British Empire possessions in the Pacific, beginning with an attack on Hong Kong almost simultaneous with the Pearl Harbor attack, brought the United Kingdom, Australia, and New Zealand into the conflict. In launching this war, Japanese leaders sought to neutralize the U.S. fleet, seize possessions rich in natural resources, and obtain strategic military bases to defend their far-flung empire.

The Pacific Ocean theater officially came into existence on March 30, 1942, when U.S. Admiral Chester Nimitz was appointed the title of “Supreme Allied Commander Pacific Ocean Areas.” In the other major theater in the Pacific region, known as the South West Pacific theater, Allied forces were commanded by U.S. General Douglas MacArthur. Both Nimitz and MacArthur, overseen by the U.S. joint chiefs and the western Allies combined chiefs of staff, applied leapfrogging and island hopping as major strategies. Forces led by Admiral Chester Nimitz, with a smaller land force and larger fleet, would advance north toward the island and capture the Gilbert and Marshall Islands and the Marianas, going generally in the direction of the Bonin Islands. The southern prong, led by General MacArthur and with larger land forces, would take the Solomons, New Guinea, the Bismarck Archipelago, advancing toward the Philippines.

Rationale and Use

Leapfrogging was based on both seaborne and air attacks to blockade and isolate Japanese bases, weakening their garrisons and reducing the Japanese ability to resupply and reinforce them. Thus, troops on islands that had been bypassed, such as the major base at Rabaul, were useless to the Japanese war effort and left to “wither on the vine.” MacArthur greatly supported this strategy in his effort to regain the Philippines. It began to be implemented in late 1943 in Operation Cartwheel. While MacArthur claimed tohave invented the strategy, it initially came out of the navy.

Leapfrogging had a number of advantages. It would allow U.S. forces to reach Japan more quickly and not expend the time, manpower, and supplies to capture every Japanese-held island on the way. It would also give the Allies the advantage of surprise and keep the Japanese off balance.

MacArthur, Roosevelt, and Nimitz in Pearl Harbor, Hawaii, July 26, 1944: This photo shows General Douglas MacArthur (left) and Admiral Chester Nimitz (right) flanking President Franklin D. Roosevelt (middle).

Chester Nimitz, fleet admiral of the U.S. Navy, played a major role in the naval history of World War II as commander in chief, U.S. Pacific Fleet (CinCPac), for U.S. naval forces and commander in chief, Pacific Ocean Areas (CinCPOA), for U.S. and Allied air, land, and sea forces.

Summarize Fleet Admiral Nimitz’s accomplishments in the Pacific

Key Takeaways

Key Points

• Ten days after the attack on Pearl Harbor, Chester W. Nimitz was selected to serve as commander in chief, U.S. Pacific Fleet, with the rank of admiral.
• As rapidly as ships, men, and material became available, Nimitz shifted to the offensive and defeated the Japanese Navy in the Battle of the Coral Sea, the pivotal Battle of Midway, and in the Solomon Islands campaign.
• In the final phases in the war in the Pacific, Nimitz attacked the Mariana Islands, inflicting a decisive defeat on the Japanese fleet in the Battle of the Philippine Sea, and capturing Saipan, Guam, and Tinian.
• In the Philippines, Nimitz’s ships turned back powerful task forces of the Japanese fleet, a historic victory in the multi-phased Battle of Leyte Gulf.
• Nimitz culminated his long-range strategy with successful amphibious assaults on Iwo Jima and Okinawa.
• On September 2, 1945, Nimitz signed for the United States when Japan formally surrendered on board the USS Missouri in Tokyo Bay.

Key Terms

• Battle of Midway: Widely regarded as the most important naval battle of the Pacific campaign of World War II. Between June 4 and 7, 1942, only six months after Japan’s attack on Pearl Harbor, and one month after the Battle of the Coral Sea, the U.S. Navy decisively defeated an Imperial Japanese Navy attack against Midway Atoll, inflicting irreparable damage on the Japanese fleet.
• Solomon Islands Campaign: A major campaign of the Pacific War of World War II that began with Japanese landings and occupation of several areas in the British Solomon Islands and Bougainville, in the Territory of New Guinea, during the first six months of 1942.
• Battle for Leyte Gulffrom: Generally considered to be the largest naval battle of World War II and, by some criteria, possibly the largest naval battle in history. It was fought in waters of the Leyte Gulf, near the Philippine islands of Leyte, Samar, and Luzon, October 23 26, 1944, between combined American and Australian forces and the Imperial Japanese Navy.
• Battle of the Coral Sea: A major naval battle in the Pacific theater of World War II between the Imperial Japanese Navy and Allied naval and air forces from the United States and Australia fought May 4–8, 1942. Although a tactical victory for the Japanese in terms of ships sunk, the battle would prove to be a strategic victory for the Allies.
• Battle of the Philippine Sea: A decisive naval battle of World War II that eliminated the Imperial Japanese Navy’s ability to conduct large-scale carrier actions (June 19–20, 1944).
• Chester W. Nimitz: A five-star admiral of the U.S. Navy (1885–1966). He held the dual role of commander in chief, U.S. Pacific Fleet (CinCPac), for US. naval forces and commander in chief, Pacific Ocean Areas (CinCPOA), for U.S. and Allied air, land, and sea forces during World War II. He was the leading U.S. Navy authority on submarines, as well as chief of the navy’s Bureau of Navigation in 1939. He served as chief of naval operations (CNO) from 1945 until 1947. He was the United States’ last surviving fleet admiral.

Ten days after the attack on Pearl Harbor on December 7, 1941, Chester W. Nimitz was selected commander in chief of the U.S. Pacific Fleet with the rank of admiral. Assuming command at the most critical period of the war in the Pacific, Nimitz, despite the losses from the attack on Pearl Harbor and the shortage of ships, planes, and supplies, successfully organized his forces to halt the Japanese advance. On March 24, 1942, the newly formed U.S.-British combined chiefs of staff issued a directive designating the Pacific theater an area of American strategic responsibility. Six days later, the U.S. Joint Chiefs of Staff (JCS) divided the theater into three areas: the Pacific Ocean Areas (POA), the South West Pacific Area (SWPA, commanded by General Douglas MacArthur), and the South East Pacific area. The JCS designated Nimitz as, “Commander in Chief, Pacific Ocean Areas,” with operational control over all Allied units (air, land, and sea) in that area.

Fleet Admiral Chester W. Nimitz: Nimitz was a five-star admiral of the U.S. Navy.

Nimitz’s War in the Pacific

As rapidly as ships, men, and material became available, Nimitz shifted to the offensive and defeated the Japanese Navy in the Battle of the Coral Sea (May 4–8, 1942), in the pivotal Battle of Midway (June 4–7, 1942), and in the Solomon Islands campaign. Prior to the Battle of the Coral Sea, Nimitz and and his staff discussed deciphered messages and agreed that the Japanese were likely initiating a major operation in the Southwest Pacific in early May with Port Moresby as the probable target. Nimitz’s staff also concluded that the Japanese operation might include carrier raids on Allied bases in Samoa and at Suva. Nimitz, after consultation with Admiral Ernest King, commander in chief of the U.S. Fleet, decided to contest the Japanese operation by sending all four of the Pacific Fleet’s available aircraft carriers to the Coral Sea. Although the Coral Sea area was under MacArthur’s command, Rear Admiral Fletcher (commanding Task Force 17) and Vice Admiral William F. Halsey (commanding Task Force 16) were directed to continue to report to Nimitz, not to MacArthur, while in the Coral Sea area.

During the Battle of Midway, Admiral Nimitz had one priceless advantage: U.S. cryptanalysts had partially broken the Japanese Navy’s JN-25b code. As a result, Nimitz knew that the Japanese had negated their numerical advantage by dividing their ships into four separate task groups, all too widely separated to be able to support each other. This dispersal resulted in few fast ships being available to escort the Carrier Striking Force, limiting the numbers of anti-aircraft guns able to protect the carriers. Nimitz calculated that the aircraft on his three carriers, plus those on Midway Island, gave the U.S. rough parity with Yamamoto’s four carriers, mainly because American carrier air groups were larger than Japanese ones. The Japanese, by contrast, remained almost totally unaware of their opponent’s true strength and dispositions even after the battle began.

In the final phases in the war in the Pacific, Nimitz attacked the Mariana Islands, inflicting a decisive defeat on the Japanese fleet in the Battle of the Philippine Sea (June 19–20, 1944; a decisive naval battle of World War II that eliminated the Imperial Japanese Navy’s ability to conduct large-scale carrier actions), and capturing Saipan, Guam, and Tinian. His fleet forces isolated enemy-held bastions of the Central and Eastern Caroline Islands and secured, in quick succession, Peleliu, Angaur, and Ulithi. In the Philippines, his ships turned back powerful task forces of the Japanese fleet, a historic victory in the multiphased Battle for Leyte Gulf from (October 24–26, 1944, the largest naval battle of World War II).

Fleet Admiral Nimitz culminated his long-range strategy by conducting successful amphibious assaults on Iwo Jima and Okinawa. In addition, Nimitz also ordered the U.S. Army Air Forces to mine the Japanese ports and waterways by air with B-29 Superfortresses in a successful mission called “Operation Starvation,” which severely interrupted the Japanese logistics. In January 1945, Nimitz moved the headquarters of the Pacific Fleet forward from Pearl Harbor to Guam for the remainder of the war.

By an act of Congress, approved December 14, 1944, the grade of fleet admiral of the U.S. Navy, the highest grade in the navy, was established and the next day, President Franklin Roosevelt appointed Admiral Nimitz to that rank. On September 2, 1945, Nimitz signed for the United States when Japan formally surrendered on board the USS Missouri in Tokyo Bay. On October 5, 1945, which had been officially designated as “Nimitz Day”in Washington, D.C., Nimitz was personally presented a Gold Star for the third award of the Distinguished Service Medal by the president of the United States, “for exceptionally meritorious service as Commander in Chief, U.S. Pacific Fleet and Pacific Ocean Areas, from June 1944 to August 1945….”

Nimitz signs Japanese surrender: Admiral Chester Nimitz, representing the United States, signs the instrument of surrender, September 2, 1945, aboard the USS Missouri in Tokyo Bay.

Operation Cartwheel (1943–1944) was a major military strategy in the Pacific theater of World War II that aimed at militarily neutralizing the major Japanese base at Rabaul and was directed by the supreme Allied commander in the South West Pacific Area (SWPA), General Douglas MacArthur.

Discuss MacArthur’s strategy in Operation Cartwheel

Key Takeaways

Key Points

• Operation Cartwheel  (1943–1944) was a major military strategy for the Allies in the Pacific theater of World War II that aimed at militarily neutralizing the major Japanese base at Rabaul (New Guinea).
• Japanese forces had captured Rabaul from Australian forces in February 1942 and turned it into their major forward base in the South Pacific, and the main obstacle in the two Allied theaters. The eventual strategic plan to take over Rabaul was formulated by General MacArthur and known as “Elkton III” or “Operation Cartwheel.”
• The offensive began with the landing at Lae by the Australian 9th Division on September 4, 1943. MacArthur eventually caught the Japanese off balance and cut off Japanese forces in the Wewak area.
• The campaign showed the effectiveness of a strategy that avoided major concentrations of enemy forces and instead aimed at severing the Japanese lines of supply and communication.
• Following the campaign, MacArthur formulated strategy for the Philippines campaign, which included the Battle of Leyte Gulf, the largest naval battle of World War II.

Key Terms

• Battle of Leyte Gulf: Generally considered to be the largest naval battle of World War II and, by some criteria, possibly the largest naval battle in history. It was fought in waters of the Leyte Gulf, near the Philippine islands of Leyte, Samar, and Luzon, October 23–26, 1944, between combined American and Australian forces and the Imperial Japanese Navy.
• Operation Cartwheel: A major military strategy for the Allies in the Pacific theater of WWII (1943–1944) that aimed at militarily neutralizing the major Japanese base at Rabaul (New Guinea).

Operation Cartwheel (1943–1944) was a major military strategy for the Allies in the Pacific theater of World War II. It aimed at militarily neutralizing the major Japanese base at Rabaul (New Guinea). The operation was directed by the supreme Allied commander in the South West Pacific Area (SWPA)— General Douglas MacArthur —whose forces advanced along the northeast coast of New Guinea and occupied nearby islands. Allied forces from the Pacific Ocean Areas command—under Admiral Chester W. Nimitz—advanced through the Solomon Islands toward Bougainville. The Allied forces involved were from Australia, the Netherlands, New Zealand, the United States, and various Pacific islands.

Strategy

Japanese forces had captured Rabaul, on New Britain, in the Territory of New Guinea, from Australian forces in February 1942 and turned it into their major forward base in the South Pacific, and the main obstacle in the two Allied theaters. MacArthur formulated a strategic outline, the Elkton Plan, to capture Rabaul from bases in Australia and New Guinea. Admiral Ernest J. King, the chief of naval operations, proposed a plan with similar elements but under navy command. Army Chief of Staff George C. Marshall, whose main goal was for the United States to concentrate its efforts against Nazi Germany in Europe and not against the Japanese in the Pacific, proposed a compromise plan in which the task would be divided into three stages, the first under navy command and the second two under MacArthur’s direction and the control of the army. This strategic plan, which was never formally adopted by the U.S. Joint Chiefs of Staff but which was ultimately implemented, called for the capture of Tulagi (later Guadalcanal ) and the Santa Cruz Islands (Operation Watchtower), the capture of the northeast coast of New Guinea and the central Solomons, and the reduction of Rabaul and related bases.

The protracted battle for Guadalcanal—followed by the unopposed seizure of the Russell Islands (Operation Cleanslate) on February 21, 1943—resulted in Japanese attempts to reinforce the area by sea. MacArthur’s air forces countered in the Battle of the Bismarck Sea (March 2–5, 1943). The disastrous losses suffered by the Japanese prompted Admiral Isoroku Yamamoto to initiate Operation I Go (or Operation “I”), a series of air attacks against Allied airfields and shipping at both Guadalcanal and New Guinea, which ultimately resulted in Yamamoto’s death.

MacArthur had presented Elkton III, his revised plan for taking Rabaul before 1944, on February 12, 1943. It called for an attack by MacArthur against northeast New Guinea and western New Britain, and by Admiral William F. Halsey, Jr. (then in command of the South Pacific Area) against the central Solomons. This plan required seven more divisions than were already in the theater, raising objections from the British. The Joint Chiefs responded with a directive that approved the plan using forces already in the theater or en route to it, and delaying its implementation by 60 days. Elkton III then became Operation Cartwheel.

Operations

In New Guinea, a country without roads, large-scale transportation of men and materials would have to be accomplished by aircraft or ships. The offensive began with the landing at Lae by the Australian 9th Division on September 4, 1943. The next day, MacArthur watched the landing at Nadzab by paratroops of the 503rd Parachute Infantry. His B-17 made the trip on three engines because one failed soon after leaving Port Moresby, but he insisted that it fly on to Nadzab. For this, he was awarded the Air Medal.

In early November, MacArthur’s plan for a westward advance along the coast of New Guinea to the Philippines was incorporated into plans for the war against Japan. Three months later, airmen reported no signs of enemy activity in the Admiralty Islands, and MacArthur ordered an amphibious landing there, commencing the Admiralty Islands campaign. It took six weeks of fierce fighting before the 1st Cavalry Division captured the islands.

MacArthur eventually caught the Japanese off balance and cut off Japanese forces in the Wewak area. Because the Japanese were not expecting an attack, the garrison was weak, and Allied casualties were correspondingly light. However, the terrain turned out to be less suitable for airbase development than first thought, forcing MacArthur to seek better locations further west. The campaign showed the effectiveness of a strategy that avoided major concentrations of enemy forces and instead aimed at severing the Japanese lines of supply and communication.

The Battle of Leyte Gulf

In July 1944, President Roosevelt summoned MacArthur to meet with him in Hawaii, “to determine the phase of action against Japan.” Nimitz and MacArthur agreed that the next step should be to advance on the southern and central Philippines. The Philippines campaign included the Battle of Leyte Gulf, the largest naval battle of World War II and, by some criteria, possibly the largest naval battle in history. Following MacArthur’s strategy, the battle was fought in waters of the Leyte Gulf, near the Philippine islands of Leyte, Samar, and Luzon, from October 23 to 26, 1944, between combined American and Australian forces and the Imperial Japanese Navy. On October 20, U.S. troops invaded the island of Leyte as part of a strategy aimed at isolating Japan from the countries it had occupied in Southeast Asia, and in particular, at depriving its forces and industry of vital oil supplies. The battle consisted of four separate engagements between the opposing forces: the Battle of the Sibuyan Sea, the Battle of Surigao Strait, the Battle of Cape Engaño, and the Battle off Samar, as well as other actions.

MacArthur in New Guinea: Left to right: Mr. Frank Forde (Australian minister for the army), General Douglas MacArthur, General Sir Thomas Blamey, Lieutenant General George C. Kenney, Lieutenant General Edmund Herring, and Brigadier General Kenneth Walker.

After Japan did not respond to a threat of destruction, the United States dropped atomic bombs on the cities of Hiroshima and Nagasaki in August 1945.

Assess the damages of the atomic bombing of Hiroshima and Nagasaki, and summarize the production of the atomic bomb through the Manhattan Project

Key Takeaways

Key Points

• The Manhattan Project, beginning in 1939 and costing $2 billion by its conclusion in 1946, was the research and development program that produced the first atomic bomb.
• Two types of atomic bomb were developed during the war. A relatively simple gun-type fission weapon was made using uranium, while a more complex plutonium implosion-type weapon was designed concurrently.
• After Japan ignored the ultimatum to surrender, on August 6, 1945, the United States dropped a uranium gun-type atomic bomb on the city of Hiroshima. Three days later, on August 9, the United States dropped a plutonium implosion-type bomb on the city of Nagasaki.
• Estimates vary greatly, but within the first two to four months of the bombings, the acute effects of the atomic bombings killed 90,000–146,000 people in Hiroshima and 39,000 80,000 in Nagasaki. Many died from the effect of burns, radiation sickness, and other injuries, compounded by illness and malnutrition.
• On August 15, 1945, six days after a second atomic bomb destroyed Nagasaki, Japan surrendered.

Key Terms

• Nagasaki: A large city in western Kyushu, in Japan. It was annihilated by the second military use of the atomic bomb on August 9, 1945.
• Hiroshima: A city in Honshu, Japan, devastated by the first atomic bomb dropped in warfare on August 6, 1945.
• Manhattan Project: A research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II.

The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. It was also charged with gathering intelligence on the German nuclear energy project. Through Operation Alsos, Manhattan Project personnel served in Europe, sometimes behind enemy lines, where they gathered nuclear materials and rounded up German scientists. In the immediate postwar years, the Manhattan Project conducted weapons testing at Bikini Atoll as part of Operation Crossroads.

From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the U.S. Army Corps of Engineers. The army component of the project was designated the “Manhattan District”; “Manhattan” gradually superseded the official code name, “Development of Substitute Materials,” for the entire project. Along the way, the Manhattan Project absorbed its earlier British counterpart, Tube Alloys.

The Manhattan Project began modestly in 1939, but grew to employ more than 130,000 (although some estimate that as many as 160,000) people and cost nearly $2 billion (roughly equivalent to $25.8 billion as of 2012). Research and production took place at more than 30 sites, some secret, across the United States, the United Kingdom, and Canada. The project maintained control over American atomic weapons research and production until the formation of the United States Atomic Energy Commission in January 1947.

Producing the Bomb

Two types of atomic bomb were developed during the war. A relatively simple gun-type fission weapon was made using uranium, while a more complex plutonium implosion-type weapon was designed concurrently. For the gun-type weapon development, uranium-235 (an isotope that makes up only 0.7 percent of natural uranium) was required. Chemically identical to the most common isotope, uranium-238, and with almost the same mass, it proved difficult to separate the two. Most of this work was performed at Oak Ridge, Tennessee.

In parallel with the work on uranium was an effort to produce plutonium. Reactors were constructed at Oak Ridge, Tennessee, and Hanford, Washington, in which uranium was irradiated and transmuted into plutonium. The plutonium was then chemically separated from the uranium. The gun-type design proved impractical to use with plutonium, so a more complex implosion-type weapon was developed in a concerted design and construction effort at the project’s weapons research and design laboratory in Los Alamos, New Mexico.

The Bombings of Hiroshima and Nagasaki

Following a firebombing campaign that destroyed many Japanese cities, the Allies prepared for a costly invasion of Japan. The war in Europe ended when Nazi Germany signed its instrument of surrender on May 8, but the Pacific War continued. Together with the United Kingdom and the Republic of China, the United States called for a surrender of Japan in the Potsdam Declaration of July 26, 1945, threatening Japan with, “prompt and utter destruction.” The Japanese government ignored this ultimatum.

On August 6, the United States dropped a uranium gun-type atomic bomb (“Little Boy”) on the city of Hiroshima. American President Harry S. Truman called for Japan’s surrender 16 hours later, warning them to, “expect a rain of ruin from the air, the like of which has never been seen on this earth.” Three days later, on August 9, the United States dropped a plutonium implosion-type bomb (“Fat Man”) on the city of Nagasaki.

Casualties and Damages

In Hiroshima, an area of approximately 4.7 square miles (12 km2) was destroyed. Japanese officials determined that 69 percent of Hiroshima’s buildings were destroyed and another 6–7 percent damaged. About 70,000 to 80,000 people, of whom 20,000 were Japanese combatants and 20,000 were Korean slave laborers, or some 30 percent of the population of Hiroshima, were killed immediately, and another 70,000 injured. The bomb in Nagasaki was dropped over the city’s industrial valley midway between the Mitsubishi Steel and Arms Works in the south and the Mitsubishi-Urakami Ordnance Works in the north. The resulting explosion had a blast yield equivalent to 21 kilotons of TNT but was confined to the Urakami Valley and a major portion of the city was protected by the intervening hills, resulting in the destruction of about 44 percent of the city. The bombing also crippled the city’s industrial production extensively and killed 23,200–28,200 Japanese industrial workers and 150 Japanese soldiers. Overall, an estimated 35,000–40,000 people were killed and 60,000 injured. Estimates vary greatly, but within the first two to four months of the bombings, the acute effects of the atomic bombings killed 90,000–146,000 people in Hiroshima and 39,000–80,000 in Nagasaki. Many died from the effect of burns, radiation sickness, and other injuries, compounded by illness and malnutrition. In both cities, most of the dead were civilians, although Hiroshima had a sizable military garrison.

The atomic bomb’s devastation: Photo of what became later Hiroshima Peace Memorial among the ruins of buildings in Hiroshima, in early October 1945.

Following the bombings, Emperor Hirohito intervened and ordered the Supreme Council for the Direction of the War to accept the terms the Allies had set down in the Potsdam Declaration for ending the war. After several more days of behind-the-scenes negotiations and a failed coup d’état, Emperor Hirohito gave a recorded radio address across the Empire on August 15. In the radio address, he announced the surrender of Japan to the Allies.

Atomic bombing of Japan: Atomic bomb mushroom clouds over Hiroshima (left) and Nagasaki (right).

After the United States dropped atomic bombs on the Japanese cities of Hiroshima and Nagasaki and the Soviet Union declared war on Japan, Emperor Hirohito surrendered.

Explain how the bombing of Hiroshima and the Soviet Union’s invasion of Manchukuo led to Emperor Hirohito’s surrender, and summarize the negotiations and final outcome of the Potsdam Conference

Key Takeaways

Key Points

• By the end of July 1945, the Imperial Japanese Navy was incapable of conducting operations, and an Allied invasion of Japan was imminent.
• At the Potsdam Conference, in addition to the Potsdam Agreement, which focused on the postwar order in Europe, on July 26, the Potsdam Declaration was issued. It outlined the terms of surrender for Japan during World War II in Asia but the Japanese ignored it.
• The subsequent bombing of Hiroshima and Nagasaki as well as the Soviet Union’s invasion of the Japanese puppet state of Manchukuo prompted the surrender of Japan.
• The surrender of Japan on September 2, 1945, brought the hostilities of World War II to a close.
• After the formal surrender, occupation and investigations into Japanese war crimes began. The state of war between Japan and the United States formally ended when the Treaty of San Francisco came into effect on April 28, 1952.

Key Terms

• Potsdam Declaration: A statement that called for the surrender of all Japanese armed forces during World War II. On July 26, 1945, U.S. President Harry S. Truman, U.K. Prime Minister Winston Churchill, and Chairman of the Nationalist Government of China Chiang Kai-shek issued the document, which outlined the terms of surrender for the Empire of Japan as agreed upon at the Potsdam Conference.
• Treaty of San Francisco: A peace agreement between Japan and Allied powers, officially signed by 48 nations on September 8, 1951, at the War Memorial Opera House in San Francisco. It came into force on April 28, 1952. The treaty served to end officially World War II, to end formally Japan’s position as an imperial power, and to allocate compensation to Allied civilians and former prisoners of war who had suffered Japanese war crimes.
• Big Six: Common term referring to the Supreme Council for the Direction of the War in Japan. The body consisted of the prime minister, minister of foreign affairs, minister of the army, minister of the navy, chief of the army general staff, and chief of the navy general staff.

By the end of July 1945, the Imperial Japanese Navy was incapable of conducting operations and an Allied invasion of Japan was imminent. While publicly stating their intent to fight on to the bitter end, Japan’s leaders at the Supreme Council for the Direction of the War (the ” Big Six “) were privately making entreaties to the neutral Soviet Union to mediate peace on terms favorable to the Japanese. The Soviets, meanwhile, were preparing to attack the Japanese, in fulfillment of their promises to the United States and the United Kingdom made at the Tehran and Yalta Conferences.

The Potsdam Declaration

The leaders of the major Allied powers met at the Potsdam Conference from July 16 to August 2, 1945. The participants were the Soviet Union, the United Kingdom, and the United States, represented by Josef Stalin, Winston Churchill (who was later replaced by Clement Attlee when the Labor Party won the British elections), and Harry S. Truman, respectively.

The Potsdam Conference: The Potsdam Conference was held at Cecilienhof, the home of Crown Prince Wilhelm Hohenzollern, in Potsdam, occupied Germany, from July 17 to August 2, 1945.

In addition to the Potsdam Agreement, which focused on the postwar order in Europe, on July 26, Churchill, Truman, and Chiang Kai-shek, Chairman of the Nationalist Government of China (the Soviet Union was not at war with Japan) issued the Potsdam Declaration, which outlined the terms of surrender for Japan during World War II in Asia.

Japan was given an ultimatum to surrender (in the name of the United States, Great Britain, and China) or meet, “prompt and utter destruction,” but the atomic bomb was not mentioned. The terms of the declaration specified the matters of Japanese authorities (e.g., the elimination of proponents of the Empire), territory (including occupation by the Allies), demilitarization, treatment of individuals defined as war criminals, postwar democracy, and economy. Contrary to what had been intended at its conception, the declaration made no direct mention of the Emperor. Allied intentions on issues of utmost importance to the Japanese, including whether Hirohito was to be regarded as one of those who had, “misled the people of Japan,” or even as a war criminal, or alternatively whether the Emperor might potentially become part of a, “peacefully inclined and responsible government,” were left unstated.

The “prompt and utter destruction” clause has been interpreted as a veiled warning about American possession of the atomic bomb which had been successfully tested in New Mexico on July 16, 1945, the day before the Potsdam Conference opened. Prime minister Kantarō Suzuki did not respond.

Occupation and Surrender

On August 6, 1945, the United States dropped an atomic bomb on the city of Hiroshima. Late in the evening of August 8, 1945, in accordance with Yalta agreements but in violation of the Soviet-Japanese Neutrality Pact, the Soviet Union declared war on Japan, and soon after midnight on August 9, 1945, it invaded the Japanese puppet state of Manchukuo. Later that day, the United States dropped an atomic bomb on Nagasaki. The combined shock of these events caused Emperor Hirohito to intervene and order the Big Six to accept the terms for ending the war that the Allies had set down in the Potsdam Declaration. After several more days of behind-the-scenes negotiations and a failed coup d’état, Hirohito gave a recorded radio address to the nation on August 15. In the radio address, he announced the surrender of Japan.

On August 28, 1945, the occupation of Japan by the supreme commander of the Allied powers began. Supreme Commander of the Allied Powers Douglass MacArthur arrived in Tokyo on August 30, and immediately decreed several laws: No Allied personnel were to assault Japanese people; no Allied personnel were to eat the scarce Japanese food; and flying the Hinomaru or “Rising Sun” flag was severely restricted. The formal surrender occurred on September 2, 1945, when representatives from the Empire of Japan signed the Japanese Instrument of Surrender in Tokyo Bay aboard the USS Missouri. Japanese Foreign Minister Shigemitsu signed for the Japanese government, while General Umezu signed for the Japanese armed forces.

After the formal surrender, investigations into Japanese war crimes began. At a meeting with MacArthur later in September, Emperor Hirohito offered to take blame for the war crimes, but his offer was rejected, and he was never tried. Legal procedures for the International Military Tribunal for the Far East were issued on January 19, 1946.

Following the signing of the instrument of surrender, many further surrender ceremonies took place across Japan’s remaining holdings in the Pacific. Japanese forces in Southeast Asia surrendered on September 12, 1945, in Singapore. Taiwan’s Retrocession Day (October 25) marked the end of Japanese rule of Taiwan and the subsequent rule by the Republic Of China government. It was not until 1947 that all prisoners held by America and Britain were repatriated. As late as April 1949, China still held more than 60,000 Japanese prisoners.

The logistical demands of the surrender were formidable. After Japan’s capitulation, more than 5,400,000 Japanese soldiers and 1,800,000 Japanese sailors were taken prisoner by the Allies. The damage done to Japan’s infrastructure, combined with a severe famine in 1946, further complicated the Allied efforts to feed the Japanese POWs and civilians.

The state of war between the United States and Japan officially ended when the Treaty of San Francisco took effect on April 28, 1952. Japan and the Soviet Union formally made peace four years later, when they signed the Soviet-Japanese Joint Declaration of 1956.

Surrender of Japan, Tokyo Bay, September 2, 1945: General of the Army Douglas MacArthur, supreme Allied commander, reading his speech to open the surrender ceremonies, on board USS Missouri (BB-63).