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[Source:] The lessons learned on Iwo Jima served as guidelines for the following Battle of Okinawa and the planned invasion of the Japanese homeland. For example, "because of the casualties taken at Iwo Jima on the first day, it was decided to make the preparatory bombardment the heaviest yet delivered on to a Pacific island"

The lessons learned on Iwo Jima served as guidelines for the following Battle of Okinawa and the planned invasion of the Japanese homeland. For example, "because of the casualties taken at Iwo Jima on the first day, it was decided to make the preparatory bombardment the heaviest yet delivered on to a Pacific island".[36] Also, in the planning for a potential attack on the Japanese home islands, it was taken into account that around a third of the troops committed to Iwo Jima and again at Okinawa had been killed or wounded.[37]

The traditional justification for Iwo Jima's strategic importance to the United States' war effort has been that it provided a landing and refueling site for long-range fighter escorts. These escorts proved both impractical and unnecessary, and only ten such missions were ever flown from Iwo Jima.[38]

Other justifications are also debatable.

Given the Japanese military's fanaticism and militancy, I'd be surprised if the US commanders for the Battle of Iwo Jima had expected any less than what did ensue? So is the above claim true? If so, why did the commanders fail to bombard more than less, in the interest of an abundance of caution? Why not shell the island for a week, if not more, before landing infantry?

Although I'm lay in history, I ask out of my sorrow for the steep casualties, which, I want to know, was truly inevitable and necessary, in view of this island's futility (as alleged above) for the rest of WWII.

Footnote: I was originally reading this forum post, and not this Wikipedia article. Also, unlike on Omaha Beach, Iwo Jima did not seem to require an element of surprise since the IJA could predict an attack?

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    You're asking multiple questions here. At least define "insufficient": depending on your idea of sufficiency, anything short of obliterating Iwo Jima with a nuclear bomb may be termed "insufficient". AFAIK American planners did not anticipate particular difficulty at Iwo Jima after a three day bombing; if so they wouldn't have felt the need to go for a full week. The bombardment of Iwo Jima was rather ineffectual in any case. – Semaphore Feb 9 '15 at 7:28
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    I'm always skeptical of questions that involve speculation "I'd be surprised ... ", and also of appeals to emotion "sorrow for the steep casualties". Each of these are signs that this is not a question, but political speech. Please address the issues that Semaphore raised. – Mark C. Wallace Feb 9 '15 at 16:26
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    This needs clarification. I'm not really sure what's being asked, and if the questions that are here can be objectively answered. This is interesting subject matter and the question shows research, so it would be especially nice if OP could hammer this into an in-scope question. – Nathan Cooper Feb 9 '15 at 19:35
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Iwo Jima was a Japanese fortress. It was designed for attrition.

First, there were artillery, mortars, and rockets on the foot and slopes of Mount Suribachi. They had walls of reinforced concrete, four feet thick. In addition, they had reinforced steel doors. These were well-protected from bombardment. They were meticulously aimed and when the Americans showed up, the Japanese just opened fire.

The bombardment did destroy all buildings, aircraft, and waters-edge defenses, but that was it. The Japanese knew these would be destroyed, so they were only a minor (if not nominal) part of their defensive strategy.

In addition, there was a huge network of underground tunnels, almost completely safe and untouched by any bombardment of any size or length. They were deep underground and the bulk of the Japanese garrison were immune down there. There were several chambers large enough to hold 300 plus men. All major chambers were connected by over eleven miles of tunnels, all deep enough to be safe from any bombardment.

During the actual bombardment, there was no Japanese response. The Americans had no idea where the Japanese artillery was. And there was an enormous amount of Japanese artillery:

General Kuribayashi had available to him 361 artillery pieces of 75 mm or larger caliber, a dozen 320 mm mortars, 65 medium (150 mm) and light (81 mm) mortars, 33 naval guns 80 mm or larger, and 94 anti-aircraft guns 75 mm or larger. In addition to this formidable array of large caliber guns, the Iwo Jima defenses could boast more than 200 20 mm and 25 mm anti-aircraft guns and 69 37 mm and 47 mm antitank guns.

The firepower of the artillery was further augmented with a variety of rockets varying from an eight-inch type that weighed 90 kg and could travel 2–3 km, to a giant 250 kg projectile that had a range of more than 7 km. Altogether, 70 rocket guns and their crews reached Iwo Jima. -- Wikipedia

As I mentioned earlier Japanese firepower was aimed before the battle. They were all concentrated on various spots about 500 meters inland. When Americans reached these points, they were hit by enormous amounts of concentrated artillery fire, prepared weeks in advance.

The Japanese knew that when the Americans attacked, they would start with a bombardment. They were ready for it and designed their defense specifically against it. No artillery technology at the time could bust into the Japanese defenses, regardless of the length of the sustained barrage.

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