Ryukyu Islands, under U.S. military governance since its conquest in 1945, hand over to Japanese control.

The Battle of Okinawa (Japanese: , Hepburn: Okinawa-sen), codenamed Operation Iceberg,:17 was a major battle of the Pacific War fought on the island of Okinawa by United States Army (USA) and United States Marine Corps (USMC) forces against the Imperial Japanese Army (IJA). 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, (L-6) by the 77th Infantry Division. The 82-day battle lasted from 1 April until 22 June 1945. After a long campaign of island hopping, the Allies were planning to use Kadena Air Base on the large island of Okinawa as a base 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 USMC 1st, 2nd, and 6th Marine Divisions, to fight on the island. The Tenth was unique in that it had its own Tactical Air Force (joint Army-Marine command), and was also supported by combined naval and amphibious forces. Opposing the Allied forces on the ground was the Japanese Thirty-Second Army.

The battle has been referred to as the "typhoon of steel" in English, and tetsu no ame ("rain of steel") or tetsu no bf ("violent wind of steel") in Japanese. The nicknames refer to the ferocity of the fighting, the intensity of Japanese kamikaze attacks and the sheer numbers of Allied ships and armored vehicles that assaulted the island. The battle was the bloodiest in the Pacific, with approximately 160,000 military casualties combined: at least 50,000 Allied and 84,166117,000 Japanese,:4734 including drafted Okinawans wearing Japanese uniforms. According to local authorities, at least 149,425 Okinawan people were killed, died by suicide or went missing, roughly half of the estimated pre-war population of about 300,000.In the naval operations surrounding the battle, both sides lost considerable numbers of ships and aircraft, including the Japanese battleship Yamato. After the battle, Okinawa provided a fleet anchorage, troop staging areas, and airfields in proximity to Japan for US forces, in preparation for a planned invasion of the Japanese home islands.

The Ryukyu Islands (琉球諸島, Ryūkyū-shotō), also known as the Nansei Islands (南西諸島, Nansei-shotō, lit. "Southwest Islands") or the Ryukyu Arc (琉球弧, Ryūkyū-ko), are a chain of Japanese islands that stretch southwest from Kyushu to Taiwan: the Ōsumi, Tokara, Amami, Okinawa, and Sakishima Islands (further divided into the Miyako and Yaeyama Islands), with Yonaguni the westernmost. The larger are mostly high islands and the smaller mostly coral. The largest is Okinawa Island.The climate of the islands ranges from humid subtropical climate (Köppen climate classification Cfa) in the north to tropical rainforest climate (Köppen climate classification Af) in the south. Precipitation is very high and is affected by the rainy season and typhoons. Except the outlying Daitō Islands, the island chain has two major geologic boundaries, the Tokara Strait (between the Tokara and Amami Islands) and the Kerama Gap (between the Okinawa and Miyako Islands). The islands beyond the Tokara Strait are characterized by their coral reefs.The Ōsumi and Tokara Islands, the northernmost of the islands, fall under the cultural sphere of the Kyushu region of Japan; the people are ethnically Japanese and speak a variation of the Kagoshima dialect of Japanese. The Amami, Okinawa, Miyako, and Yaeyama Islands have a native population collectively called the Ryukyuan people, named for the former Ryukyu Kingdom that ruled them. The varied Ryukyuan languages are traditionally spoken on these islands, and the major islands have their own distinct languages. In modern times, the Japanese language is the primary language of the islands, with the Okinawan Japanese dialect prevalently spoken. The outlying Daitō Islands were uninhabited until the Meiji period, when their development was started mainly by people from the Izu Islands south of Tokyo, with the people there speaking the Hachijō language.Administratively, the islands are divided into Kagoshima Prefecture (specifically the islands administered by Kagoshima District, Kumage Subprefecture/District, and Ōshima Subprefecture/District) in the north and Okinawa Prefecture in the south, with the divide between the Amami and Okinawa Islands, with the Daitō Islands part of Okinawa Prefecture. The northern (Kagoshima) islands are collectively called the Satsunan Islands, while the southern part of the chain (Okinawa Prefecture) are called the Ryukyu Islands.