Major General DK Palit VrC (Retd)

Plans for the 1945 invasion of Japan–code-named Operation Downfall – were kept hidden in the National Archives in Washington for nearly four decades. It is only recently that they have been declassified and made public. So far, few people had been aware of the elaborate plans the Americans had made for the invasion of the Japanese home islands, and even fewer knew anything about the defences the Japanese had prepared to counter the invasion they had expected.

Operation Downfall was finalised during the summer of 1945. It called for two massive military invasions to be carried out in succession, aimed at the heart of the Japanese Empire. In the first invasion – code-named Parhelion Olympic – 14 combat divisions of US Marines and the US Army were to land on the southernmost of the Japanese home islands, the heavily fortified and defended Kyushu, after an unprecedented naval and aerial bombardment. The second invasion was to take place four months later, on 1 March 1946 – code-named Operation Coronet – and would land at least 22 divisions against the one million defenders on the main island of Honshu and the plain of Tokyo, the capital city – which, it was estimated, would bring about the surrender of Japan.

During the summer of 1945, with battles raging in Europe and in the Pacific, American staffs had little time to prepare for such an awesome endeavour. Some even suggested that a naval blockade combined with strategic bombing of Japan might be sufficient, but neither General MacArthur nor the Joint Chiefs of Staff in Washington believed that blockade-and-bombing would bring about an unconditional surrender The advocates for invasion agreed that while a blockade may choke, it would not kill and though strategic bombing may destroy cities, it would leave whole armies intact. So on 25 May 1945, the Joint Chiefs of Staff, after considerable deliberation, issued to General MacArthur, Fleet Admiral Chester Nimitz, and Army Air Force General Hap Arnold, a topsecret directive to proceed with the invasion of Japan–target date, after the typhoon season.

President Truman approved the plans for the invasions on
24 July. Two days later the United Nations issued the Potsdam Proclamation, calling upon Japan to surrender unconditionally or face total destruction. Three days later, Tokyo announced to the world that Japan would ignore the proclamation and would refuse to surrender. It was learned through monitoring Japanese radio broadcasts during this period that Japan had ordered the shutdown of all schools to mobilise its schoolchildren, armed its civilians, fortified caves and built miles and miles of underground defences (However, the Japanese had kept their real defensive plans a closely guarded secret.)

The first US invasion, Operation Olympic, called for a four-pronged attack on Kyushu, with the aim of seizing and controlling the southern end of the island, establishing naval and air bases, tightening the naval blockade, destroying units of the Japanese land forces and preparing to support the invasion of the Tokyo Plain.

As the invasion grew imminent, the massive firepower of the Third and Fifth Fleets of the US Navy would approach Japan. The Third under Admiral Halsey would consist of battleships, heavy cruisers, and destroyers, dozens of support ships and three fast carrier task groups. From these carriers, hundreds of navy fighters, dive bombers and torpedo planes would strike at targets all over Honshu. Admiral Spruance's 3,000 ship Fifth Fleet would carry the invasion troops. For several days prior to the invasion, battleships, heavy cruisers, and destroyers would pour thousands of tons of high explosives into the target areas and not cease the bombardment until after the invading land forces had been launched.

The invasion of the main island of Kyushu would begin on 1 November, with thousands of Marine and army soldiers wading ashore on beaches all along the eastern, south-eastern, southern and western coasts of Kyushu. Waves of aircraft from 66 aircraft carriers would saturate the enemy defences, gun emplacements, and troop concentrations along the beaches.

In the light of the Pentagon's intelligence estimates of the state of Japanese defensive deployments in their home islands, the above US forces were considered to be more than adequate for the task. It now transpires that American Intelligence on the state of Japanese defences was a downright underestimation. Captured Japanese documents and interrogation of Japanese military leaders after the war disclose that the US information, especially concerning the number of Japanese planes – both fighters and bombers–was dangerously in error.

During the preliminary sea battle in Okinawa alone, Japanese Kamikaze aircraft sank 32 Allied ships and damaged over 400 others, whereas during the summer of 1945, American top brass had determined that the Japanese had exhausted their airpower at the battle for Okinawa – based on the fact that American fighters and bombers daily flew unmolested over Japan. What the US Intelligence did NOT know was that after the end of July, the Japanese had decided to conserve all their aircraft, their pilots and their fuel stocks for the decisive battle for the home islands.

As part of the plan for the defence of the home islands – code-named “Ketsu-Go" – the Japanese had built 20 take-off strips for suicide attacks in southern Kyushu, with underground hangars invisible to air recce. In addition, they had 35 camouflaged airfields and 9 sea-plane bases (none detected by the US air recce.) In addition, the Japanese were building newer and more efficient models of the "Okka", a rocket-propelled bomb much like the German V-1, but flown by suicide pilots. They had planned to launch 50 seaplane bombers, 100 carrier-based aircraft and 50 land-based army bombers in suicide attacks on the US fleet. Apart from home-based aircraft, the Japanese had 58 more airfields in Korea, Western Honshu and Shikoku, all to be used for massive suicide attacks.

The US intelligence had assessed that the Japanese had no more than a total of 2,500 aircraft, of whom only 300 were to be deployed in suicide attacks. The actual situation, however, was that in August 1946 (unknown to the U S Intelligence) the Japanese still had 5,651 army and 7,074 naval fighters and bombers. Furthermore, aircraft manufacturing and repair facilities had been organised in every village and township. Hidden in mines, railway tunnels, under viaducts and in the basements of department stores, mini-factories had been constructed for the manufacture of aircraft parts.

"Ketsu-Go" called for a four-fold aerial plan of attack when the US invasion became imminent – to destroy up to 800 Allied ships. While Allied invasion ships were approaching Japan but were still well out to sea, an initial force of 2,000 army and naval fighters were "to fight to the death" to dominate the skies over Kyushu. A second force of 330 naval combat force were to attack the main body of the invading fleets to prevent them from using their fire support and air cover to protect the troop-carrying transports. After these two forces had been launched, a third force of 825 suicide planes was to strike at the invading transport ships. Furthermore. as the invasion fleets approached their anchorages, another 2,000 kamikaze planes were to be launched in waves of 200 to 300, to be used in hour-by-hour attacks. By mid-morning of the first day of the invasion, most of the American land-based aircraft would be forced to return to their land-based airfields, leaving the defence against the kamikaze attacks to the carrier pilots and the ship-based anti-aircraft guns.

The American carrier pilots would have to land on their carriers time and time again to rearm and refuel and thus become crippled by fatigue : gun crews would become exhausted – but still the waves of kamikazes would continue. With the American ships hovering off the beaches, all remaining Japanese aircraft would be committed to non-stop suicide attacks (which the Japanese hoped, could be sustained for 10 days) coordinate these strikes with attacks from the remaining submarines from the Imperial Navy – some armed with Long Lance torpedoes with a range of 20 miles–when the invasion fleet was still 180 miles away from Kyushu.

The Imperial Japanese Navy still had two cruisers and
23 destroyers that were operational. They were to be used to counter-attack the invasion. A number of the destroyers were to be beached at the last minute, to be used as anti-invasion gun platforms. Once, they reached the invasion shores, the invading fleet would be forced to defend themselves not only against attacks from the air, but also against suicide attacks from the sea. Japan had trained a suicide naval attack unit of midget submarines, human torpedoes and exploding motorboats.

The Japanese aimed to shatter the invasion before it had a chance to land, convinced that the Americans would back off or become so demoralised as to accept a less-than-unconditional surrender - and a more honourable and face-saving end for the Japanese. However, as horrible as the battle for Japan would be off the beaches, it would be on Japanese soil that the Americans would meet up against the most fanatical and desperate defensive battles they had encountered anywhere during the War.

During the island-hopping campaigns in the Pacific and in the Philippines, Allied troops had always outnumbered the Japanese by two to one and sometimes even by three to one. It would be different on the main Japanese homeland. Firstly, by virtue of cunning, brilliant military reasoning and guesswork, the Japanese high command had been able to deduce not only when but also where the Americans would land their invasion forces. Based on those deductions, they had made their defensive dispositions.

Facing the fourteen American divisions landing at Kyushu would be fourteen Japanese divisions, seven independent mixed brigades, three armoured brigades and many thousands of naval troops. On Kyushu, the odds would be three to two in favour of the defenders – 700,000 defenders against 550,000 Americans. And this time the bulk of the defenders would not be the poorly trained and ill-equipped labour battalions that the US invading forces had faced in their earlier campaigns-island-hopping in the Pacific-but the hard core of the Japanese regular home army, familiar with the terrain, with stockpiles of arms and ammunition, and with an effective supply and transport organisation almost invisible from the air. Many of the defending troops were the elite of the Imperial Japanese Army, driven by a fanatical offensive spirit.

Japan's network of beach defences consisted of offshore mine-fields in the sea approaches, thousands of suicide scuba divers attacking landing craft and inter-locked mine-fields on the beaches. To face the invading amphibious assault landings, the Japanese had deployed three divisions with a back-up counter-attack force of two divisions. Awaiting the south-eastern attack at Ariake Bay was an entire marine division and at least one mixed infantry brigade. But the most brutal opposition the US Marines would face would be on the western shores of Kyushu Island: three Japanese divisions, an armoured brigade, a mixed infantry brigade and an artillery command. Components of two further divisions were ear-marked for the role of counter-attacks.

The battle for Japan would be fought in what was termed "Prairie Dog Warfare" – a type of fire almost unknown to the ground troops who fought in Europe and North Africa, in which battles were fought – as in the Pacific islands – for every yard, foot and sometimes inch of the ground – a brutal, deadly form of combat as seen at Tarawa, Saipan, Iwo Jima and Okinawa.

In the mountains behind the beaches a series of underground networks of caves, bunkers, command posts and field hospitals had been dug in, connected by miles and miles of tunnels with dozens of entrances and exits. Some of these complexes could hold up to 1,000 troops each.

In addition to the use of poison gas and bacteriological warfare, (which the Japanese had experimented with) Japan had mobilised its citizenry including women and children to take an active part in the beach battles. Had Olympic come about, the Japanese people, inflamed by the national slogan "One hundred Million Will Die for the Emperor and the Nation", were prepared to fight to the death. 28 million Japanese had become a part of the National Volunteer Combat Force, armed with rifles, lunge mines, satchel charges, Molotov cocktails and one-shot black powder mortars. Others were armed with swords, long bows, axes and bamboo spears. These civilian units were to be used in night attacks, hit-and-run raids, delaying actions and massive suicide charges at the invaders. It was estimated that at the earlier stages of the invasion, 1,000 Japanese and American soldiers would be dying every hour.

Intelligence studies in Washington and military estimates made 50 years ago-and not after-the-event speculation – indicate that the battle for Japan would have resulted in the biggest blood-bath in the history of warfare. Far worse would have been the fate of Japan as a nation and as a culture. The invasion would have been preceded by several months of fire bombing all the remaining Japanese cities. The cost of human lives that resulted from the two atomic blasts would have been small in comparison to the total number of Japanese lives that would have been lost in this aerial devastation. Furthermore, with American forces locked in combat in the south of Japan, little would have prevented the Soviet Union from occupying the northern half of the Japanese islands. Japan today could be divided much like Korea – or Germany as she was after the war.