The Battle of Okinawa, code named Operation Iceberg, was a major battle of the Pacific War fought on the island of Okinawa by United States Marine and Army forces against the Imperial Japanese Army. The initial invasion of Okinawa on April 1, 1945, was the largest amphibious assault in the Pacific Theater of World War II. The 82-day battle lasted from April 1 until June 22, 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 7th, 27th, 77th, and 96th infantry divisions of the US Army with the 1st, 2nd, and 6th divisions of the Marine Corps, 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.

The battle has been referred to as the "typhoon of steel" in English, and tetsu no ame ("rain of steel") or tetsu no bōfū ("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 one of the bloodiest in the Pacific, with approximately 160,000 casualties on both sides: at least 75,000 Allied and 84,166–117,000 Japanese, including drafted Okinawans wearing Japanese uniforms. 149,425 Okinawans were killed, committed suicide or went missing, a significant proportion of the estimated pre-war 300,000 local population.

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 in preparation for a planned invasion. 

In all, the US Army had over 103,000 soldiers (of these, 38,000+ were non-divisional artillery, combat support and HQ troops, with another 9,000 service troops), over 88,000 Marines and 18,000 Navy personnel (mostly Seabees and medical personnel). At the start of the Battle of Okinawa, the US 10th Army had 182,821 personnel under its command. It was planned that General Buckner would report to Turner until the amphibious phase was completed, after which he would report directly to Spruance. Although Allied land forces were entirely composed of American units, the British Pacific Fleet (BPF; known to the US Navy as Task Force 57) provided about ¼ of Allied naval air power (450 planes). It comprised a force which included 50 warships, of which 17 were aircraft carriers; while the British armored flight decks meant that fewer planes could be carried in a single aircraft carrier, they were more resistant to kamikaze strikes.

Although all the BPF aircraft carriers were provided by Britain, the carrier group was a combined British Commonwealth fleet with Australian, New Zealand and Canadian ships and personnel. Their mission was to neutralize Japanese airfields in the Sakishima Islands and provide air cover against Japanese kamikaze attacks. Most of the air-to-air fighters and the small dive bombers and strike aircraft were US Navy carrier-based airplanes. 

The Japanese land campaign (mainly defensive) was conducted by the 67,000-strong (77,000 according to some sources) regular 32nd Army and some 9,000 Imperial Japanese Navy (IJN) troops at Oroku Naval Base (only a few hundred of whom had been trained and equipped for ground combat), supported by 39,000drafted local Ryukyuan people (including 24,000 hastily drafted rear militia called Boeitai and 15,000 non-uniformed laborers). The Japanese had used kamikaze tactics since the Battle of Leyte Gulf, but for the first time, they became a major part of the defense. Between the American landing on April 1 and May 25, seven major kamikaze attacks were attempted, involving more than 1,500 planes.

The 32nd Army initially consisted of the 9th, 24th, and 62nd Divisions, and the 44th Independent Mixed Brigade. The 9th Division was moved to Taiwan before the invasion, resulting in shuffling of Japanese defensive plans. Primary resistance was to be led in the south by Lieutenant General Mitsuru Ushijima, his chief of staff, Lieutenant General Isamu Chō and his chief of operations, Colonel Hiromichi Yahara. Yahara advocated a defensive strategy, whilst Chō advocated an offensive one.

In the north, Colonel Takehido Udo was in command. The IJN troops were led by Rear Admiral Minoru Ōta. They expected the Americans to land 6–10 divisions against the Japanese garrison of two and a half divisions. The staff calculated that superior quality and numbers of weapons gave each US division five or six times thefirepower of a Japanese division. To this, would be added the Americans' abundant naval and air firepower.