The Battle of Okinawa, also known as Operation Iceberg, was fought on the Ryukyu Islands of Okinawa and was the largest amphibious assault in the Pacific Theater of World War II. The United States Navy assembled an unprecedented armada in April of 1945 The American invasion of Okinawa was the largest amphibious assault of World War II The 82 day battle lasted from late March through June 1945. 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 gunfire involved, and sheer numbers of Allied ships and armored vehicles that assaulted the island. The battle has one of the highest number of casualties of any World War Two engagement: the Japanese lost over 100,000 troops, and the Allies (mostly United States) suffered more than 50,000 casualties, with over 12,000 killed in action. Hundreds of thousands of civilians were killed, wounded or attempted suicide. Approximately one-fourth of the civilian population died due to the invasion. The main objective of the operation was to seize a large island only 340 miles away from mainland Japan. After a long campaign of island hopping, the Allies were approaching Japan, and Okinawa would serve as a springboard for the planned invasion of the mainland islands. Although hastily converted to a base for air operations, the atomic bombings of Hiroshima and Nagasaki caused Japan to surrender just weeks after the end of the fighting at Okinawa and the invasion never took place.