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 Tenth United States Army was the last army level command established during the Pacific War during World War II, and included divisions from both the U.S. Army and the U.S. Marine Corps.