The Battle of Okinawa, codenamed Operation Iceberg, was fought on the Ryukyu Islands of Okinawa and was the largest amphibious assault in the Pacific War of WWII. The 82-day-long battle lasted from early April until mid-June 1945. The Allies planned to use Okinawa as a base for air operations in the invasion of mainland Japan, Operation Downfall.
On the Japanese front, Okinawa made Japan a "defeated and demoralized nation." The peace party leaders in Tokyo were forced to admit that defeat was inevitable. Their arguments convinced Emperor Hirohito to oppose the pro-war leaders in his cabinet, and after Hiroshima and Nagasaki, to accept unconditional surrender... Finally, at Okinawa, American forces destroyed the Imperial Army. The crippling of Japan's vessels and the elimination of all fuel supplies forced an end to the Japanese war machine.
The battle for Okinawa cost the Fifth Fleet dearly: 36 ships sunk, 368 damaged, 4,900 men killed or drowned, another 4,800 wounded, 763 aircraft lost. Among the 145 ships sunk or so heavily damaged as to be out of action for 30 days or more, four were lost to mines, five to suicide small craft, three to coastal batteries, and 133 to Japanese air attacks. In the fighting ashore, the Tenth Army sustained nearly 40,000 combat casualties, plus an additional 26,000 “non-battle” casualties, primarily combat fatigue cases. Tens of thousands of Okinawan civilians died in the fighting.
Mass surrender of the Japanese did not begin until 10th Army crowded them to the water’s edge. As General Ushijima concluded the activities of 32nd Army within the cave system near Mabuni, American soldiers of 7th Infantry Division began to arrive at the entrance to the cave at the top. Japanese soldiers blasted the opening to seal themselves inside. General Ushijima radioed his last message to Tokyo on the evening 21st June. Realizing that they could hold out no longer, he and his chief of staff, General Cho, readied themselves for death. In the early hours of the following morning both men appear at the mouth of the cave facing the east, the time for the honoured rites of hara-kiri had arrived.
The last Japanese defensive line fell along the Yaeju-Dake and Yuza-Dake hill mass in the central part of the island in the south. General Ushijima had arrived here around 4th June just ahead of the Americans... From 6th June Army Divisions began to probe the eastern face of the Japanese positions with limited success. Flame Thrower Tanks now became the American solution to the Japanese Coral Caves and the battle raged with orange rods of flame, shells, rockets and bombs. In the centre 96th Infantry Division launched a night attack against the ridge between the two peaks of Yaeju-Dake and Yuza-Dake and established a toehold. The next day 12th June, by evening both divisions had forced the Japanese off most of the forward positions.
Fierce resistance was gradually overcome toward the end of May as the Americans pressed Shuri itself from three sides... The island's defenders realized that they had inflicted severe casualties on the Americans--some twenty-six thousand between the two attacking corps, the heaviest of the Pacific war--but the Japanese had suffered even more devastating losses, some sixty-four thousand killed in the fighting around Shuri alone. The issue before the Japanese commanders was a simple one: should the 32d Army make its stand at Shuri, which would ultimately be overwhelmed, or attempt a retreat to secondary defensive positions in the south? ...Determined to cause as much harm as possible to the American invaders, the Japanese officers decided to attempt a tactical redeployment farther south.
It rained being the rainy season, the road got to be mud and sometime knee deep where you couldn’t get one foot out ahead of the other and it was just too hard to describe. Trucks were getting stuck even the tanks had to be reequipped with wider treads to be able to move in the mud. I think this area was the most depressing because the offensive to take Shuri Castle area had become a stale mate and every morning we would start out with the same thing, a big barrage which we would keep up for about a half hour or so, with very intense firing. Our infantry would try to move up and they would be blown away and that lasted for a week or longer.
[Lieutenant General] Buckner was now faced with an obvious choice: He had absolute control of the sea, with the exception of the kamikazes. He could attempt a landing on southernmost Okinawa, thereby bypassing the fortifications, or he could use direct frontal assaults to reduce the Japanese positions... Instead Buckner decided to implement something of a compromise: a direct frontal assault but with a double envelopment, which would push forward on both his right and left flanks at the same time. Given the casualties engendered, it would probably have been wiser to attempt a landing on southern Okinawa.
Buckner continued to experience trouble in pushing south, but the problem was evidently now isolated and was most evident on his right flank... The Machinato Line was pierced on April 24, although the Americans encountered a second line, the Shuri, a few days later.
Yamato, lead ship of a class of two 65,000-ton (over 72,800-tons at full load) battleships, was built at Kure, Japan. She and her sister, Musashi were by far the largest battleships ever built... Their nine 460mm (18.1-inch) main battery guns, which fired 1460kg (3200 pound) armor piercing shells, were the largest battleship guns ever to go to sea, and the two ships' scale of armor protection was also unsurpassed.
Yamato... was assigned to take part in the suicidal "Ten-Go" Operation, a combined air and sea effort to destroy American naval forces supporting the invasion of Okinawa. On 7 April 1945, while still some 200 miles north of Okinawa, Yamato was attacked by a massive force of U.S. carrier planes and sunk.
The cloudy April weather reduced visibility, thus skewing the digitally-generated aerial maps of the island. From the erroneous information, Americans estimated 65,000 Japanese troops; in reality, more than 100,000 troops awaited, hidden in a maze of tunnels and caves... One American veteran described the onslaught: "While on Okinawa, the marines and soldiers were going through their crucible of hell brought on by rain, heat, poison snakes, mosquitoes...the stench of human feces and rotting human flesh filled with maggots..."
Since the opening of the campaign on 1 April, seven battered and broken destroyers and many of their gallant crews had been dispatched to their watery graves by the fiery onslaught of the fanatical kamikazes. Except for submarines, no ship was immune from the ravages of the "Divine Wind," which had killed and wounded their crews by the thousands and crippled and mangled over 100 ships before the island was ultimately taken.
The Okinawa defense force issued a directive to Okinawan prefectural citizens calling for unification of the army, government and civilians living together and dying together (kyosei kyoshi), and stating that even a single tree or blade of grass should be a fighting power. They mobilized for battle all people, down to young and old, women and children.
The military and paramilitary locally recruited in Okinawa numbered more than 25,000 (soldiers on active duty, drafted soldiers, defense units, student units, volunteer units, etc.). We have to realize that one fourth of the Okinawa defense force were “Japanese soldiers” coming out of Okinawa prefecture. It is a mistake to think that Japanese forces in the battle of Okinawa were exclusively officers and men from the mainland (Yamato troops).
The United States Navy assembled an unprecedented armada in April of 1945, with 1,300 ships laying in wait off the coast of Okinawa. In fact, the effort in the spring offensive of 1945 was far greater than the previous spring offensive in Europe. During the Normandy invasion, the Allies had employed 150,000 troops, 284 ships, and 570,000 tons of supplies, all of which required a very short supply line. On Okinawa, in Japan's back yard, maintaining the supply line seemed an incomprehensible feat. In the invasion of Okinawa, there were 183,000 troops, 327 ships, and 750,000 tons of supplies.
These final operations before the invasion of Japan, the first phase of which was targeted against Kyushu (Operation Olympic) and scheduled for November 1945, were codenamed Detachment (Iwo Jima), Iceberg (the overall operation), Bunkhouse (the Ryukyu Islands) and Scattering (Okinawa itself). The securing of the Philippines would mean that Japanese forces in the Dutch East Indies would be cut off from the home islands. B-29s could continuously bomb Japan from their bases in the Mariana Islands and the seizure of Iwo Jima and Okinawa would mean that the Japanese would not have bases directly in their flight path from which to intercept them and provide bases from which the Americans could provide the bombers with fighter protection and emergency airfields that damaged bombers could land on. It would also mean additional flank protection as the Americans would be in a better position to stop Japanese aircraft from Formosa and China intercepting the bombers.