Japanese naval operation in World War II
, also known as Operation Heaven One (or Ten-ichi-gō 天一号), was the last major Japanese naval operation in the Pacific Theater of World War II. In April 1945, the , the largest battleship in the world, and nine other Japanese warships, embarked from Japan for a suicide attack on Allied forces engaged in the Battle of Okinawa. The Japanese force was attacked by U.S. carrier-borne aircraft before it could reach Okinawa; "Yamato" and five other Japanese warships were sunk. 
The battle demonstrated U.S. air supremacy in the Asiatic-Pacific Theater and the vulnerability of surface ships without air cover to aerial attack. The battle also exhibited Japan's willingness to make extreme sacrifices in "kamikaze" attacks aimed at delaying the Allied advance upon the Japanese home islands.
Furthermore, the engagement was also paramount by enabling U.S. forces to prevent Japan from holding a significant advantage over the Allies at Okinawa. The designation of "Yamato" as a beached fortification against Allied aerial and naval bombardment of Okinawa would have become detrimental towards the invading armies, in that, alike to Operation Downfall, the anticipated losses would have substantially increased for maritime combatants at large, likewise with surrounding infantry support. It is generally accepted amongst historians that the prior removal of "Yamato" from the scene was a preliminary objective of the Allies before any further assaults.
Background.
By early 1945, following the Solomon Islands campaign, the Battle of the Philippine Sea and the Battle of Leyte Gulf, the once-formidable Imperial Japanese Navy's Combined Fleet was reduced to just a handful of operational warships and a few remaining aircraft and aircrew. Most of the remaining Japanese warships in the Combined Fleet were stationed at ports in Japan, with most of the large ships at the port of Kure in the Hiroshima Prefecture on the main Japanese island of Honshu.
As a final step before the planned invasion of the Japanese home islands, Allied forces invaded Okinawa on 1 April 1945. In March, when briefing Emperor Hirohito on Japan's response to the expected invasion of Okinawa, Japanese military leaders explained that the Imperial Japanese Army was planning extensive air attacks, including the use of "kamikaze" tactics. The emperor then reportedly asked, "But what about the Navy? What are they doing to assist in defending Okinawa? Have we no more ships?" Feeling pressured by the emperor to mount some kind of attack, Japanese Navy commanders conceived a "kamikaze"-type mission for their remaining operational large ships, which included the battleship .
The resulting plan, drafted under the direction of the Commander-in-Chief of the Combined Fleet, Admiral Soemu Toyoda, called for "Yamato" and her escorts to attack the U.S. fleet supporting troops landing on the western coast of Okinawa. "Yamato" and her escorts were to fight their way to Okinawa and then beach themselves between Higashi and Yomitan and fight as shore batteries until they were destroyed. Once the ships were destroyed, their surviving crew members were supposed to abandon ship and fight on land. Very little, if any, air cover could be provided for the ships, which would render them almost helpless to concentrated attacks from U.S. carrier-based aircraft. In preparation for executing the plan, on 29 March the assigned ships left Kure for Tokuyama, off the port of Mitajiri on the southern coast of Honshu. Despite obeying orders to prepare for the mission, the commander of the "Ten-Go" force, Vice-Admiral Seiichi Itō, still refused to actually order his ships to carry it out, believing the plan to be futile and wasteful.
Other officers of the Imperial Japanese Navy also had very negative views about the operation, believing that it was a waste of human life and fuel. Captain Atsushi Ōi, an operations officer at Grand Escort Command, was critical as fuel and resources were diverted from other operations. As he was told that the aim of this operation was "the tradition and the glory of the Navy," he shouted: "this war is of our nation and why should the honor of our 'surface fleet' be more respected? Who cares about their glory? Damn fools!".
Vice Admiral Ryūnosuke Kusaka flew from Tokyo to Tokuyama on 5 April in a final attempt to convince Itō and the assembled commanders of the Combined Fleet to accept the plan. Upon hearing of the proposed operation—which had been kept secret from most of them—the Combined Fleet commanders and captains unanimously joined Itō in rejecting it for the same reasons that he had expressed. Kusaka then explained that the Navy's attack would help divert U.S. aircraft away from the Army's planned kamikaze attacks on the U.S. fleet at Okinawa. He also explained that Japan's national leadership, including the emperor, were expecting the Navy to make their best effort to support the defense of Okinawa.
Upon hearing this, the Combined Fleet commanders relented and accepted the proposed plan. The ships' crews were briefed on the nature of the mission and given the opportunity to stay behind if desired; none did. However, approximately 80 crew members who were new, sick, or infirm were ordered off the ships, including 67 naval cadets of Etajima Naval Academy Class No. 74 who had arrived on the battleship three days earlier. The ships' crews engaged in some last-minute intense drills to prepare for the mission, mostly practicing damage control procedures. At midnight, the ships were fueled. Reportedly, in secret defiance of orders to provide the ships with only just enough fuel to reach Okinawa, the Tokuyama personnel actually gave "Yamato" and the other ships almost all of the remaining fuel in the port, although this probably still was not enough to allow the force to return to Japan from Okinawa. "Yamato"'s executive officer organised a party for the crew for the evening of 5 April, during which many of the officers and sailors drank heavily.
The United States Navy was able to monitor preparations for Operation Ten-Go by decoding Japanese radio signals. Through this source, the Americans received conclusive intelligence on 5 and 6 April that the attack was to be attempted. Admiral Raymond Spruance, commander of the United States Fifth Fleet, ordered his forces to prepare to attack the Japanese at 00:30 on 6 April, before "Yamato" and her escorts sailed.
Prelude.
At 16:00 on 6 April, "Yamato" (with Admiral Itō on board), the light cruiser , and eight destroyers (, , , , , , , and ) departed Tokuyama to begin the mission. Two American submarines, and , sighted the Japanese force as it proceeded south through the Bungo Channel. Although they were unable to attack because of the ships' speed, they did spend several hours shadowing the Japanese sortie and sending updates on its course to the U.S. fleet. The submarines' messages, which were reportedly sent uncoded, were also picked up by radio operators on the Japanese ships.
At dawn on 7 April, the Japanese force passed the Ōsumi Peninsula into the open ocean heading south from Kyūshū toward Okinawa. They shifted into a defensive formation, with "Yahagi" leading "Yamato" and the eight destroyers deployed in a ring around the two larger ships, with each ship from each other and proceeding at . The destroyer "Asashimo" developed engine trouble and turned back. U.S. reconnaissance aircraft began to shadow the main force of ships. At 10:00, the force turned west to make it look like they were withdrawing, but at 11:30, after being detected by two American PBM Mariner flying boats, the "Yamato" fired a salvo with her bow guns using special but could not prevent the two planes from shadowing. The forces then turned back towards Okinawa.
Upon receiving contact reports early on 7 April, Spruance ordered Task Force 54, which consisted mostly of modernized Standard-type battleships under the command of Rear Admiral Morton Deyo (which were engaged in shore bombardment), to intercept and destroy the Japanese sortie. Deyo moved to execute his orders, but Vice Admiral Marc A. Mitscher, who commanded Task Force 58, preempted Spruance and Deyo by launching a massive air strike from his carriers, without informing Spruance until after the launches were completed. As a senior naval aviation officer, "Mitscher had spent a career fighting the battleship admirals who had steered the navy’s thinking for most of the current century. One of those was his immediate superior, Raymond Spruance. Mitscher felt a stirring of battleship versus aircraft carrier rivalry. Though the carriers had mostly fought the great battles of the Pacific, whether air power alone could prevail over a surface force had not been proven beyond all doubt. Here was an opportunity to end the debate forever".
Around 10:00 on 7 April, Task Groups 58.1 and 58.3 began launching 280 aircraft from their carriers. Task Group 58.4 launched a further 106 aircraft. The aircraft consisted of F6F Hellcat and F4U Corsair fighters, SB2C Helldiver dive bombers, and TBF Avenger torpedo bombers. Overall, 15 carriers launched aircraft. The air groups launched from five carriers became lost in bad weather and were not able to attack. As a contingency, Spruance ordered Deyo to assemble a force of six fast battleships, seven cruisers and 21 destroyers to prepare for a surface engagement with "Yamato" should the airstrikes prove unsuccessful.
Battle.
Around noon, the first American aircraft arrived over "Yamato"; these were F6F Hellcat and F4U Corsair fighters conducting a fighter sweep of any Japanese aircraft defending the battle group; however, the severely depleted Imperial Japanese Army Air Force could muster no opposition, which allowed U.S. dive-bomber and torpedo aircraft to set up for their attacks unmolested. These aircraft—after a two-hour flight from Okinawa—arrived over the "Yamato" battle group and circled the ship formation just out of anti-aircraft range; the lack of Japanese fighter resistance provided ample breathing room for American crews to methodically plan and coordinate their attack runs. 
The first wave of U.S. carrier planes was spotted by a Japanese lookout on the bridge at 12:32. Two minutes later, at 12:34, "Yamato" opened fire with her 460 mm main batteries. The ships stopped zigzagging and increased speed to , began taking evasive maneuvers, and opened fire with their anti-aircraft guns. "Yamato" carried almost 150 anti-aircraft guns, including her massive 460 mm main guns that fired San Shiki anti-aircraft shells. The U.S. pilots deduced that the use of San Shiki and colored gunfire meant that "Yamato's" gunners relied on visual aiming and range, rather than being radar directed, and as a result "were missing with great consistency" despite the storm of fire that they put up.
The Hellcat and Corsair fighters "were supposed to go first, to strafe, to rocket, to drop light ordnance, distracting the enemy gunners while the Helldivers plunged almost straight down with their heavy [armor piercing] bombs". This was because the Avenger torpedo bombers "needed all the distraction and diversion they could get when they made their dangerous low altitude runs straight at the enemy ships." The Avengers mainly attacked from the port side so that if the torpedoes hit that side, it would increase the likelihood of the target ship capsizing.
At 12:46, a torpedo hit "Yahagi" directly in her engine room, killing the entire engineering room crew and bringing her to a complete stop. "Yahagi" was hit by at least six more torpedoes and 12 bombs by succeeding waves of air attacks. The destroyer "Isokaze" attempted to come to "Yahagi"'s aid but was attacked and heavily damaged and sank sometime later. "Yahagi" capsized and sank at 14:05.
During the first attack wave, despite evasive maneuvers that caused most of the bombs and torpedoes aimed at her to miss, "Yamato" was hit by two armor-piercing bombs and one torpedo. Her speed was not affected, but one of the bombs started a fire aft of the superstructure that was not extinguished. Also, during the first attack wave, destroyers "Hamakaze" and "Suzutsuki" were heavily damaged and taken out of the battle. "Hamakaze" sank later.
Between 13:20 and 14:15, the second and third waves of U.S. aircraft attacked, concentrating on "Yamato". During this time, "Yamato" was hit by at least eight torpedoes and up to 15 bombs. The bombs did extensive damage to the topside of the ship, including knocking out power to the gun directors and forcing the anti-aircraft guns to be individually and manually aimed and fired, greatly reducing their effectiveness. The torpedo hits—almost all on the port side—caused "Yamato" to list enough that capsizing was an imminent danger.
At 13:33, in a desperate