My younger brother, who has a hard time seeing me be right on anything, announced that it was impossible to know what the effects of a conventional invasion would have been, and therefore it was impossible to say that it would have been worse than the atomic bombs.
He's wrong. We know what the effects of an invasion would have been, and they would have been horrific.
Primary Sources on my Website:
Strategic Plan for DOWNFALL -- 28 May 1945
Requirements for Land Based and Carrier-Based Aircraft to accomplish the Defeat of Japan -- 9 August 1945
The Japanese Plans for the Defense of Kyushu - 31 December 1945
White House Meeting on the Invasion of Japan - 18 June 1945
Anyway. You can see in the White House Meeting Document, the casualty ratio of the last couple of operations in the Pacific.
Leyte: 17,000 US vs 78,000 Japanese (1:4.6 Ratio)
Luzon: 31,000 US vs 156,000 Japanese (1:5 Ratio)
Iwo Jima: 20,000 US vs 25,000 Japanese (1:1.25 Ratio)
Okiwana: 34,000 US vs 81,000 Japanese (1:2 Ratio)
Total: 102,000 US vs 340,000 Japanese (1:3.3 Ratio)
If you go to the Japanese Plans for the Defense of Kyushu, you will see that the Japanese had massed about 680,000 men (14 division equivalents) in Kyushu just before the end of the war.
If we assume we have to wound/kill 60% of the Japanese troops to ensure victory in Kyushu (unlike the island campaigns, this is an area where the Japanese can retreat; they're not locked into a area of a few square miles) then US casualties for Kyushu alone would be:
Best Case (Luzon): 81,600
Median Case (Average): 123,600
Worst Case (Okiwana): 204,000
(I did not use Iwo Jima for "worst case" as it was only 8 square miles; compared to Okiwana's 463 square miles).
On top of this; you have the Manhattan Project looming over the place:
Hull-Seaman Conversation on 13 August 1945
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Seamans: The biggest gap will be between the one now [19 August] and the one for the first part of September. After that, I would say approximately one every ten days.
.....
Seamans: Nearer the tactical use rather than other use.
Hull: That is what it amounts to. What is your own personal reaction to that?
Seamans: I have studied that a poor deal. Our own troops would have to be about six miles away I am not sure that the Air Forces could place it within 500 feet of the point we want. Of course, it is not that "pinpoint". Then the stage of development has to be considered. The work it is liable to be used for the more or less has to be explosive effect. It would be just a gamble putting or sending those troops though.
Hull: Not the same day or anything like that. We might do it a couple or three days before. You plan to land on a certain beach. Behind which you know there is a good road communication and maybe a division or two of Japanese troops. Neutralization of that at some time from H Hour of the landing back earlier, maybe a day or two or three. I don't anticipate that you would be dropping it as we do other type bombs that are in support of the infantry. I am thinking about neutralizing a division or a communication center or something so that it would facilitate the movement ashore of troops.
Seamans: That is the preferable use at this time from that standpoint. The weapon we have is not a penetration weapon. The workmanship is not as good as possible. It is much better than average workmanship. We are still developing it though.
Hull: From this on more or less of the timing factor, how much time before the troops actually go into that area do you think would be the safety factor? Suppose you did get a dud or an incomplete explosion, what safety factor should you consider, one, two, three days?
Seamans: I think we are sending some people over to actually measure that factor. I think certainly by within 48 hours that could be done. Everything is going so fast. We would like to train people and get them in a combat spirit to do that. I think the people we have are the best qualified in that line. Of course, as you say, if it is used back in a kind of reserve line or in a reserve position or a concentration area but that you wouldn't be up against right away.
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That would have been fun, with US troops wading ashore on D-Day with mushroom clouds on the horizon as we nuke Japanese troop concentrations to prevent their movement towards the beaches.
As for the millions of Japanese casualties...we're already up to 408,000 (60% of 680,000) for military personnel alone.
It's not very well known; but Japan suffered an agricultural collapse at around this exact time.
Japanese Statistics Bureau Page
Table 7-14 Planted Area and Agricultural Production (1878--2004) LINK
1940: 3,152,000 hectares planted -- 9,131,000 tons of rice produced
1941: 3,156,000 hectares planted -- 8,263,000 tons of rice produced
1942: 3,138,000 hectares planted -- 10,016,000 tons of rice produced
1943: 3,084,000 hectares planted -- 9,433,000 tons of rice produced
1944: 2,955,000 hectares planted -- 8,784,000 tons of rice produced
1945: 2,869,000 hectares planted -- 5,872,000 tons of rice produced <--- wow!
1946: 2,781,000 hectares planted -- 9,208,000 tons of rice produced
Rice harvests collapsed; and that was the main staple food of the Japanese at the time.
Normally, in an event like this; the Japanese would just have imported rice from their holdings in Manchuria and Korea to make up the shortfall -- in effect, starve Koreans or Chinese to feed Japanese.
But...due to Operation Starvation; Japanese shipping essentially died. For example, tonnage through Kobe went from 320,000 tons in March to 44,000 tons in July.
The mining operation sank or damaged 670 Japanese ships of 1.2 million tons and 35 of 47 essential convoy routes had to be abandoned.
At first; the STARVATION efforts were concentrated on closing the Shimonoseki Straits to merchant shipping -- 80% of the Japanese merchant marine passed through it, along with blocking the Inland Sea ports of Toyko and Nagoya.
But towards the end of the war, Korean ports and ports in Northern Japan were targeted by the mine-laying B-29s in an aim to close off the Sea of Japan; which was already an American Lake -- wolfpacks of American submarines were operating inside it.
So we're easily looking at mass starvation in Japan as they divert what little rice they have towards military units which are needed to fight the US invasion.
And they would have had sent a lot of attacks against the US Invasion forces:
12 x Destroyers to carry suicide torpedoes to attack transports
40 x Submarines
1,000 x Suicide Explosive Motor Boats
30 x Midget Submarines
50 x Suicide Torpedoes
100 x Small Submarines
800 x Kamikaze Aircraft (my OCR program gave me a typo and gave me 300 instead of 800).
Historically, about 14 percent of Kamikazes survived to score a hit against a ship; and 8.5 percent of all ships hit by Kamikazes sank.
So that comes out to 112 ships hit by Kamikazes in any invasion of Kyushu; of which nine will sink.
The Japanese expected they would get at least 60 transports with these measures -- and if we cut their numbers in half; that's still 30 transports; and if we assume each transport carries 400 troops; that's 12,000 American soldiers who die before they even set foot on the Japanese Homeland.
And this is just OLYMPIC. CORONET is set to go off in 1946 against Tokyo and the plains around it.
