And now the end of the war in the Pacific.
Chapter VI: Conclusion of the Pacific War, 1943-1945.
In much of Europe it was forgotten – and many suffering in Eastern Europe as the Nazis’ horrible masterplan unfolded probably didn’t care – that the Second World War wasn’t over yet. Japan was wounded and on the retreat, but not yet defeated. After being defeated at Guadalcanal, the Japanese launched an offensive into India and counteroffensives in China. With hundreds of thousands of soldiers redeployed from North Africa and the Middle East to India, the British not only repulsed the Japanese offensive but also retook most of Burma and reopened the Burma Road in late 1943. Large amounts of Lend-Lease Aid were subsequently sent to Chiang Kai-shek’s Kuomintang, enabling him to mitigate the effects of Japan’s 1944 offensives.
In 1944, the US also invaded Saipan (part of the Marianas) and seized control of the island despite the fanatical resistance of the Japanese garrison, which resulted in most of the defenders dying in combat in a hellish battle. Japanese commanders saw holding Saipan as imperative and sent nine carriers with 473 planes, five battleships, several cruisers, and 28 destroyers to destroy the US Fifth Fleet (which had fifteen fleet carriers and 956 planes, seven battleships, 28 submarines, and 69 destroyers, as well as several light and heavy cruisers). The Battle of the Philippine Sea was an American victory.
After the disaster at Philippine Sea the Japanese were left with two choices: either to commit their remaining strength in an all-out offensive or to sit by while the Americans occupied the Philippines and cut the sea lanes between Japan and the vital resources from the Dutch East Indies and Malaya. The plan devised by the Japanese was a final attempt to create a decisive battle by utilizing their last remaining strength, which included the firepower of its heavy cruisers and battleships, which was to be all committed against the American beachhead at Leyte. With Japanese codes cracked, forces that were qualitatively superior at this point and a numerical superiority enhanced by US Navy units transferred from the Atlantic, the Battle of Leyte Gulf was an Allied victory that crippled Japanese naval capabilities.
The US expanded their operations in the Philippines and reduced the Japanese presence to pockets. In February the Battle of Iwo Jima followed: The Battle of Iwo Jima (“Operation Detachment”) in February 1945 was one of the bloodiest battles fought by the Americans in the Pacific War. Iwo Jima is a 21 square kilometre island situated halfway between Tokyo and the Marianas. Holland Smith, the commander of the invasion force, aimed to capture the island and prevent its use as an early-warning station against air raids on the Japanese Home Islands, and to use it as an emergency landing field. Lieutenant-General Tadamichi Kuribayashi, the commander of the defence of Iwo Jima, knew that he could not win the battle, but he hoped to make the Americans suffer far more than they could endure. Massive networks of interconnected bunkers and hidden guns survived American bombardment and inflicted appalling losses to the US Marines, but they pressed on against devastating machine gun and artillery fire. Iwo Jima fell in late March.
In the meantime, the British had been very busy building more airfields, small riverports, roads, railroads and bridges in Burma to improve their logistics there in preparation for offensives into Southeast Asia in 1944. Over 1 million troops had arrived in the six months after mid-1943 and the infrastructure needed to supply so many had to be built. 1.5 million British and Commonwealth forces, 250.000 Chinese troops and 50.000 American soldiers now opposed little over 300.000 Japanese troops that still controlled a mountainous sliver of Burmese territory separated from the rest of the country by the Salween River. Outnumbering them 6:1, the Allied success in the offensives that started in January 1944 is hardly surprising: Japanese forces were kicked out of Burma and Thailand turned on its Japanese masters after they saw which way the wind was blowing, declaring war on their erstwhile ally in February 1944. Thailand switching sides quickly cut off Japanese forces in Malaysia from resupply by land, and they weren’t getting much by sea either as British and American submarines increased in numbers vastly after the end of the war in Europe, prowling in the waters of East Asia and Southeast Asia and targeting oil tankers and cargo ships. By the time the monsoon started in June, making further campaigning impossible, the Allies had retaken Malaya and its important rubber plantations and had also made inroads into occupied French Indochina. As part of an agreement between the Free French and Vichy, France formally declared war and sent 15.000 men to fight there.
After the monsoon ended in October, French Indochina fell and the Allies could now aid China militarily directly by launching offensives into southern China. Chiang Kai-shek’s forces now received so many Lend-Lease deliveries they could equip thirty divisions up to American standards with M1 Garand semi-automatic rifles, Browning machine guns, M24 Chaffee light tank and M4 Sherman medium tanks; six Chinese fighter squadrons got P51 Mustangs and three Chinese bomber squadrons were formed with B-25 Mitchell medium bombers. Together, Chinese and Anglo-American forces combed through southern China and had eliminated the Japanese presence by March 1945. In August 1945, the Kuomintang was able to liberate Nanjing. Back in Southeast Asia, the Allies invaded Borneo and Sumatra, upon which the Dutch re-joined the Pacific War.
The largest and bloodiest American battle came at Okinawa, as the US sought airbases for 3.000 B-29 bombers and 240 squadrons of B-17 bombers for the intense bombardment of Japan’s home islands in preparation for a full-scale invasion in late 1945. The Japanese, with 115.000 troops augmented by thousands of civilians on the heavily populated island, did not resist on the beaches – their strategy was to maximize the number of soldier and Marine casualties, and naval losses from Kamikaze attacks. After an intense bombardment the Americans landed on April 1st 1945 and declared victory on June 21st 1945. The supporting naval forces were the targets for 4.000 sorties, many by Kamikaze suicide planes. US losses totalled 38 ships of all types sunk and 368 damaged with 4.900 sailors killed. The Americans suffered 75.000 casualties on the ground; 94% of the Japanese soldiers died along with many civilians. The British Pacific Fleet operated as a separate unit from the American task forces in the Okinawa operation. Its objective was to strike airfields on the chain of islands between Formosa and Okinawa, to prevent the Japanese from reinforcing the defences of Okinawa from that direction.
After experiencing the extreme determination of Japanese defenders on Iwo Jima and Okinawa, US military planners had to assume not only resistance from all available troops the Empire of Japan could muster but also from a fanatically hostile civilian population. They believed Operation Downfall would be the costliest campaign in American military history: In April 1945, the Joint Chiefs of Staff formally adopted a planning paper giving a range of possible casualties based on experience in both Europe and the Pacific for Operation Olympic (the invasion of Kyushu, the first episode of Downfall). Given a troop list of 766.700 men and a 90-day campaign, the US Sixth Army could be expected to suffer between 514.072 casualties (including 134.556 dead and missing) under the “Pacific Experience” (1.95 dead and missing and 7.45 total casualties/1,000 men/day). This assessment included neither casualties suffered after the 90-day mark (US planners envisioned switching to the tactical defensive by X+120), nor personnel losses at sea from Japanese air attacks. In order to sustain the campaign on Kyushu, planners estimated a replacement stream of 100.000 men per month would be necessary. In the spring of 1945, the Army Service Forces under Lieutenant-General Brehon B. Somervell were working under a figure of “approximately” 720.000 for the projected replacements needed for “dead and evacuated wounded” through December 31st 1946, which was for the whole invasion, including Honshu. These figures are for Army and Army Air Force personnel only, and do not include replacements needed for the Navy and Marine Corps. A study done for Secretary of War Henry Stimson’s staff by William Shockley estimated that invading Japan would cost 1.7-4 million American casualties, including 400.000-800.000 fatalities, and five to ten million Japanese fatalities. The key assumption was large-scale participation by civilians in the defence of Japan.
And then something was achieved that vindicated the $2 billion spent ($22 billion in today’s money), rewarding the work of the 130.000 men working on it and made sure the last six years’ time weren’t a waste after all. The first nuclear device ever detonated was an implosion-type bomb at the Trinity test, conducted at New Mexico’s Alamogordo Bombing and Gunnery Range on July 16th 1945. At that point, with a yield equivalent to 20 kilotons of TNT, it was the largest explosion ever produced by man (and no-one could imagine that less than a decade into the future such a bomb was a pipsqueak next to multi megaton weapons). In the San Francisco Conference in July 1945 Eden was informed of this success by President Harry S. Truman (he had succeeded Roosevelt, who had died on Monday June 18th 1945). In the San Francisco Declaration, Japan was threatened with “prompt and utter destruction” unless it surrendered unconditionally. Japan ignored this threat.
Given predictions of appalling losses, Truman decided to postpone the invasion of Japan indefinitely and maintain a naval blockade to starve Japan into submission while obliterating its cities one at a time with nuclear weapons. On August 6th 1945 the Little Boy gun-type uranium based weapon was dropped on Hiroshima, an embarkation port and industrial centre that was the site of a major military headquarters too. The 15 kiloton explosion tore through the city and killed 20.000 soldiers while estimates of civilian casualties range from 70.000 to 126.000. The Japanese didn’t surrender and in response the US deployed the Fat Man weapon, which was a spherical implosion-type nuclear weapon containing a core of about 6.4 kilograms (14 lbs) of plutonium. Nagasaki – a major military port, one of Japan's largest shipbuilding and repair centres, and an important producer of naval ordnance – was the second target on August 9th and the 21 kiloton explosion caused massive devastation and 39.000-80.000 casualties.
Japan still insisted on a conditional surrender without reparations, without an Allied occupation, no military restrictions and being allowed to keep Korea, Taiwan and possibly Manchukuo. Japan, after all, still held on to these territories and significant parts of China and Southeast Asia. Major Kenji Hatanaka, along with Lieutenant Colonels Masataka Ida, Masahiko Takeshita (the brother-in-law of General Korechika Anami, the Minister of War), Inaba Masao, and Colonel Okitsugu Arao, the Chief of the Military Affairs Section, launched a coup d’état. The conspirators had tried to gain support in the ministry and from several generals, but didn’t get it; they pressed forward nonetheless and got the support from several crucial Imperial Guards divisions through faked orders. In an armoured train, the Emperor and his family were moved to the Matsushiro Underground Imperial Headquarters, a large underground bunker complex under the mountains near Nagano. It included an underground palace fit for the Emperor and it was thought that it could survive a nuclear attack. Hatanaka, the leader of the coup, became Prime Minister.
The Americans responded to Japan’s obstinacy with more nuclear attacks. Two more Fat Man assemblies were sent to Tinian while the scientists at Los Alamos worked around the clock to cast another plutonium core*. The next available core was flown to Tinian on August 19th and the weapon was assembled and ready for use two days later, upon which Kokura, the site of one of the largest ammunitions plants of Japan, was hit on August 21st and heavily damaged by a 20 kiloton blast. On September 5th, a B-29 bomber dropped another atomic bomb (again +- 20 kilotons) on Niigata, a port with industrial facilities including steel and aluminium plants and an oil refinery. In order to demonstrate to the obstinate Japanese junta that he meant business, Truman decided to save up the two bombs that were still being assembled to launch two sorties on one day. On September 21st 1945 a double attack took place. One bomb was dropped on Yokohama, an urban centre for aircraft manufacture, machine tools, docks, electrical equipment and oil refineries. The second one was dropped on Osaka, a major centre of commerce, a major population centre, and the home of iron works and textile industry. The junta now finally realized the Americans would continue dropping atomic bombs until Japan had either been wiped off the face of the Earth or had surrendered unconditionally. On September 25th Japan announced its unconditional surrender, thus ending the Second World War.
*OTL's
Demon Core that killed Harry Daghlian and Louis Slotin in two criticality incidents. Needless to say their OTL deaths are butterflied away.