Operation Downfall in the context of "Surrender of Japan"

On 6 and 9 August 1945, the United States detonated two atomic bombs over the Japanese cities of Hiroshima and Nagasaki, respectively, during World War II. The aerial bombings killed 150,000 to 246,000 people, most of whom were civilians, and remain the only uses of nuclear weapons in an armed conflict. Japan announced its surrender to the Allies on 15 August, six days after the bombing of Nagasaki and the Soviet Union's declaration of war against Japan and invasion of Manchuria. The Japanese government signed an instrument of surrender on 2 September, ending the war.

In the final year of World War II, the Allies prepared for a costly invasion of the Japanese mainland. This undertaking was preceded by a conventional bombing and firebombing campaign that devastated 64 Japanese cities, including an operation on Tokyo. The war in Europe concluded when Germany surrendered on 8 May 1945, and the Allies turned their full attention to the Pacific War. By July 1945, the Allies' Manhattan Project had produced two types of atomic bombs: "Little Boy", an enriched uranium gun-type fission weapon, and "Fat Man", a plutonium implosion-type nuclear weapon. The 509th Composite Group of the U.S. Army Air Forces was trained and equipped with the specialized Silverplate version of the Boeing B-29 Superfortress, and deployed to Tinian in the Mariana Islands. The Allies called for the unconditional surrender of the Imperial Japanese Armed Forces in the Potsdam Declaration on 26 July 1945, the alternative being "prompt and utter destruction". The Japanese government ignored the ultimatum.

The Battle of Okinawa (Japanese: 沖縄戦, Hepburn: Okinawa-sen), codenamed Operation Iceberg, was a major battle of the Pacific War fought on the island of Okinawa by the United States Army and United States Marine Corps forces against the Imperial Japanese Army. The initial invasion of Okinawa on 1 April 1945 was the largest amphibious assault in the Pacific Theater of World War II. The Kerama Islands surrounding Okinawa were preemptively captured on 26 March 1945 by the U.S. Army 77th Infantry Division. The 82-day battle on Okinawa lasted from 1 April 1945 until 22 June 1945. After a long campaign of island hopping, the Allies were planning to use Kadena Air Base on the island as a staging point for Operation Downfall, the planned invasion of the Japanese home islands, 340 mi (550 km) away.

The United States created the Tenth Army, a cross-branch force consisting of the U.S. Army 7th, 27th, 77th and 96th Infantry Divisions with the 1st, 2nd, and 6th Marine Divisions, to seize the island. The Tenth Army was unique because it had its own Tactical Air Force (joint Army-Marine command) and was supported by combined naval and amphibious forces. Opposing the Allied forces on the ground was the Japanese Lieutenant General Mitsuru Ushijima's Thirty-Second Army, a mixed force consisting of regular army troops, naval infantry and conscripted local Okinawans. There were about 100,000 Japanese troops on Okinawa at the onset of the invasion. The battle was the longest sustained carrier campaign of the Second World War.

The 6th Marine Division was a United States Marine Corps World War II infantry division formed in September 1944. During the invasion of Okinawa it saw combat at Yae-Take and Sugar Loaf Hill and was awarded a Presidential Unit Citation. The 6th Division had also prepared for the invasion of Japan before the war ended. After the war it served in Tsingtao, China, where the division was disbanded on April 1, 1946, being the only Marine division to be formed and disbanded overseas and never set foot in the United States.