The Invasion That Never WasMainland Japan
By May 1945, as bitter fighting continued on Okinawa and Americans celebrated Germany's surrender, Pacific strategists had developed detailed plans for Operation Downfall, the two-phased invasion of the Japanese home islands to begin on 1 November. More than 5 million Allied troops would conduct the two largest planned amphibious assaults in history. As planned, all six Marine divisions and three Marine aircraft wings would play major combat roles.
By May 1945, as bitter fighting continued on Okinawa and Americans celebrated Germany's surrender, Pacific strategists had developed detailed plans for Operation Downfall, the two-phased invasion of the Japanese home islands to begin on 1 November. More than 5 million Allied troops would conduct the two largest planned amphibious assaults in history. As planned, all six Marine divisions and three Marine aircraft wings would play major combat roles.
Operation Olympic, the first phase of Operation Downfall, would involve the seizure of southern Kyushu by 14 divisions of the U.S. Sixth Army. Their objectives were to seize airfields, harbors, and staging areas for the subsequent buildup and launching of Operation Coronet, the amphibious assault by 23 divisions of the U. S. First and Eighth Armies on 1 March 1946 against the industrial and political heart of Japan, the Kanto Plain on Honshu. The Marine ground component for Olympic was V Amphibious Corps, composed of the 2d, 3d, and 5th Marine Divisions, under the command of Major General Harry Schmidt. For Coronet it was III Amphibious Corps (1st, 4th, and 6th Marine Divisions) under Major General Keller E. Rockey.
On 1 November, three corps of three divisions each would conduct simultaneous amphibious assaults against three separate locations on southern Kyushu. General Schmidt's V Amphibious Corps would seize a beachhead near Kushikino and then clear the Satsuma Peninsula, bordering the west side of Kagoshima Bay. The Army's XI Corps would land at Ariake Bay and take the eastern peninsula. I Corps would land further up the island's east coast. The three corps would move north and establish a defensive line, stretching from Sendai in the west to Tsuno in the east, effectively blocking Japanese reinforcements from moving south through the central mountains. If needed, a fourth corps and two additional divisions would reinforce the three assault corps.
The Japanese defensive plan for Kyushu encompassed three phases. First, thousands of suicide aircraft and boats would attack the American fleet, targeting troop transports in an effort to disrupt the landings. Second, newly organized defense divisions occupying heavy fortifications overlooking the beaches, would attempt to prevent the landing force from gaining a foothold. Finally, mobile divisions based inland would counterattack toward threatened positions. In August 1945, Japanese ground forces on Kyushu consisted of 14 divisions and several independent brigades, about 600,000 die-hard troops, most of whom were deployed near the invasion area.
The Japanese defensive plan for Kyushu encompassed three phases. First, thousands of suicide aircraft and boats would attack the American fleet, targeting troop transports in an effort to disrupt the landings. Second, newly organized defense divisions occupying heavy fortifications overlooking the beaches, would attempt to prevent the landing force from gaining a foothold. Finally, mobile divisions based inland would counterattack toward threatened positions. In August 1945, Japanese ground forces on Kyushu consisted of 14 divisions and several independent brigades, about 600,000 die-hard troops, most of whom were deployed near the invasion area.
Ideally, an attacking force should have at least a three-to-one superiority in numbers over the defenders. On Kyushu, American and Japanese ground forces would be of almost equal strength. In addition to regular military units, Allied forces would also face a large citizen militia, armed with whatever was at hand. The battle was expected to be bloody and costly. Lieutenant General Thomas A. Wornham, who commanded the 27th Marines and would have taken part in the assault, later noted that when he commanded the 3d Marine Division he would often commute between Japan and Okinawa and "we'd fly right over Kagoshima, and you could see the beaches where Operation Olympic was to be. ... Every time I flew over I'd say: 'Thank God that the Japanese decided to call the war off when they did, because I don't think any of us would have made it.' It was pretty wild country down there."
With Kyushu-based fighters furnishing air support, Operation Coronet would be launched in March 1946. First Army would land two corps abreast at Katakai and Choshi on the Pacific Coast east of Tokyo. The XXIV Corps (three divisions) and General Rockey's III Amphibious Corps would seize the peninsula flanking Tokyo Bay. The Eighth Army's two corps would land at Sagami Bay and seize the vital Yokohama-Yokosuka port complex. In subsequent operations, the First Army would advance on Tokyo from the east while the Eighth Army would attack the capital from the southwest. Facing Allied troops would be nine divisions totalling some 300,000 men, with an additional 27 to 35 divisions available as reinforcement.
The dropping of the atomic bombs ended the war and the need for an invasion of the Japanese home islands. If the invasion had proceeded, it would have been costly. While there is no way to accurately predict casualties, there is no doubt that the Japanese would have suffered immense losses, both military and civilian, dwarfing those inflicted by the atomic bombs. And American casualties certainly would have been in the hundreds of thousands.
(NOAH'S NOTE) I was on Okinawa at the time as a member of the First Marine Division. The dropping of the atomic bombs saved my life since it was not necessary to invade mainland Japan. Thanks to President Harry S. Truman, I live today in the year of 2009.
