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The Battle of Okinawa was one of the bloodiest and most difficult of WW2. But, if I understand correctly, most of the casualties were incurred during the fighting for the southern part of the island. Considering that the sole use of Okinawa for the Americans was as a base and stepping stone for the invasion of mainland Japan, why was the capture of the south necessary?

At the time of the battle the Japanese garrison had no hope of resupply so the Americans could have just captured Yontan airfield and enough territory around it to prevent artillery attacks and then let the Japanese either starve in their positions or waste themselves in hopeless attacks against a defensive line. Why did the Americans insist on an extremely difficult and, to my mind, pointless capture of the southern part of Okinawa?

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    Maybe I'm mistaken, but I feel the question shows a reasonable amount of research. In particular, he mentioned distinctions between different sides of the island, the purpose for the US taking it, the key airfield that needed to be taken, the condition of the Japanese garrison, reasons for an alternative strategy, that kind of thing. He has researched this. The only thing missing is references, but I don't see us requiring them on all of our other questions. – Panzercrisis Jun 4 at 14:24
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    Seems like they wouldn't starve in their positions because the civilians there would starve first. – axsvl77 Jun 4 at 14:30
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    @Panzercrisis Already discussed in History Meta read this meta question – CGCampbell Jun 4 at 21:43
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    @CGCampbell Okay, I provided an alternative: history.meta.stackexchange.com/a/4126/19153 – Panzercrisis Jun 4 at 21:57
  • one of the bloodiest — what? It's not even in the top 10 in number of casualties, there were 10× more casualties in the battle for Berlin and 10-50× more in the battle/siege for Leningrad (Okinawa ranks 20th in WW II battles). – gerrit Jun 5 at 13:42
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There are some misconceptions in the question which need to be cleared up, and doing so will go some way towards answering the question as posed.

The following is sourced from the official US military history of the operation which can be found online here:-

Okinawa: The Last Battle (CMH 1993 ed.)

Firstly, the specific purpose of the mission as conceived and planned was primarily to secure the southern part of the island, as this was where the best roads, the major port on the island, the best anchorage, the existing airfields, and the terrain deemed most suitable for further airfield construction were all located. It was also where three quarters of the population were located, and it was hoped that some of these might be employed as a labour force.

Secondly, the planned US Okinawa military base was not intended solely for supporting the invasion of Japan, there were also potential operations against Formosa and the east coast of China under consideration which were also to be supported from Okinawa, should they eventuate. One secure airbase was far less than what the Americans were hoping to achieve here.

Thirdly, and probably most significantly in answering the question, US intelligence relating to the terrain of Okinawa was very limited prior to the operation, and it was expected that only 8 airfields would be developed on the island. After examining the island at first hand it was found that 18 airfields could be sustained, including those suitable for long range bombers, so the rugged northern part of the island had been neglected as strategically useless prior to close examination, and planning of the operation reflected this. The perceived lack of strategic value of the north was also shared by the Japanese as evidenced by their decision to barely defend the northern part of the island themselves.

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  • This answers most of my question. But considering the Japanese supply situation wouldn't a siege have been preferable? Yes, there were time constraints and the possibility of the Japanese having lots of stored supplies, but the battle was horrific and the Japanese had lots of mouths to feed. Was this strategy considered at any point? – Johnny Jun 4 at 18:41
  • "Was this strategy considered at any point" ... reads like a new question... – CGCampbell Jun 4 at 21:38
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    @Johnny Did the Allies ever capture anything from the Japanese other than by fighting for it? Elsewhere the Japanese threw themselves off cliffs and resorted to cannibalism before they would consider surrendering, not to mention that most of the cultivated land on Okinawa was also in the south, so they would have had some food supplies at least. The Americans assumed 2 -3 months would be required to get their airbases operational. The long-range bombers flew their one-and-only mission from Okinawa on the very last day of the war. So I think the time constraints were probably a key factor. – Agent Orange Jun 5 at 11:31
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First, you need to remember that the US was expecting to use Okinawa as a military, naval and air base for at least two years. None of the commanders involved knew about the Manhattan Project. They were invading Okinawa in April 1945, expecting the invasion of Japan to start in November with an invasion of Kyushu, and the invasion of the largest Japanese island, Honshu, in early 1946. The surrender of Japan in response to Hiroshima and Nagasaki was a surprise to most of the US leadership.

They wanted Okinawa to be a secure base. If there were still active Japanese forces on the island, it could not be properly secure. No defensive line is truly proof against brave men who are prepared to take risks to sneak through it, so there would have always been a few Japanese loose in the base areas. They would also have gone around the ends of the line, by swimming or in small boats. Having enemy soldiers around forces every unit to post sentries, and means nobody can really relax. Having a safe area makes life much easier for troops who aren't on duty.

Further, the troops holding the defensive line would not be available for the invasion of Japan, which was going to need all the available force. It was a very worrying prospect for the US commanders, who knew that they were going to be up against a fanatical population as well as the Japanese military. Estimates of casualties were horrifying, and Okinawa was a reasonable place to put hospitals. Nobody wants enemy troops near those.

The invasion was regarded by both sides as a small-scale version of what an invasion of Japan proper would be like. So it was important for training and discovering the right methods for this kind of combat, and for learning how to minimise casualties. The Japanese had stacked the deck by providing large amounts of artillery and ammunition for it, which was another compelling reason for taking the whole island: while their artillery was active in the south, much of the island could be bombarded.

Finally, the south of the island was where the airfields were, along with the major population centres and the ports. The landing was at the waist of the island, because the beaches there were the most suitable place, but the south was the territory that would serve as bases. Sources: Okinawa: the last battle, p. 10, the relevant volume of the US Army's official history, and Nemesis: the Battle for Japan, by Max Hastings.

It would be more sensible to ask why conquering the north of the island was necessary, but all of the reasons above about a safe base area apply. This is basic military strategy. It was quite clear that securing all of Okinawa was the right thing to do.

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    Good answer. In addition:(1) The U.S. also had no idea in advance what casualties would be in step of the advance. (2) it was regarded,by both sides, as a small scale simulation of, and training for, what the invasion of the Japanese home islands would be like. Neither side knew that Hiroshima and Nagasaki would make that all moot. – Pieter Geerkens Jun 3 at 21:55
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    This looks like a good answer but it would be nice to have some sources for this other than just a Wikipedia link. Can you add? – Lars Bosteen Jun 4 at 3:03
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    It's not clear from OP's question, but I wonder if perhaps some of it might be asking why invade Okinawa at all? Japan was contained, so forcing surrender by pushing the invasion into the mainland was one option. The other might have been to simply blockade the entire country and wait them out in a defensive posture with Japan effectively under siege. With Okinawa such a bloody fight, why force the issue instead of just a contain and defend strategy? Maybe that's a separate question. – J... Jun 4 at 14:39
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    Interesting fact: the casualty estimates for the invasion of Japan were so horrifying the US commissioned the manufacture of a massive number of Purple Heart medals with the expectation that they would all be needed. The invasion never happened, and the total number of casualties in all US military actions since then have not surmounted that number. The exact number is sketchy, but Purple Heart medals from that production run are still given out today. – Seth R Jun 4 at 16:23
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    About what Seth R wrote – CGCampbell Jun 4 at 21:37

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