Planning for the Battle of Iwo Jima

In anticipation of the Battle of Iwo Jima, Lieutenant General Tadamichi Kuribayashi prepared a defense that broke with Japanese military doctrine.

Even before the fall of Saipan in June 1944, Japanese planners knew that Iwo Jima would have to be reinforced significantly if it were to be held for any length of time, and preparations were made to send sizable numbers of men and quantities of materiel to that island.

For water's edge defense to work, it needed support from the air and sea, none of which the Japanese Imperial Navy was capable of mounting at this point anymore.

To this end, mining engineers were dispatched from Japan to draw blueprints for projected underground fortifications that would consist of elaborate tunnels at varying levels to assure good ventilation and minimize the effect of bombs or shells exploding near the entrances or exits.

The admiral, a renowned Japanese aviator, had been crippled in an airplane crash in the mid-twenties and, ever since the outbreak of the war, had chafed under repeated rear echelon assignments.

The Japanese were quick to discover that the black volcanic ash that existed in abundance all over the island could be converted into concrete of superior quality when mixed with cement.

While the Japanese on Peleliu Island in the Western Carolines, also awaiting American invasion, had turned the improvement of natural caves into an art, the defenders of Iwo Jima developed it into a science.

In order to prevent personnel from becoming trapped in any one excavation, the subterranean installations were provided with multiple entrances and exits, as well as stairways and interconnecting passageways.

General Kuribayashi established his command post in the northern part of the island, about 500 m northeast of Kita village and south of Kitano Point.

Nearby, on an elevation just southeast of the station, an enormously large blockhouse was constructed which served as the headquarters of Colonel Chosaku Kaidō, who commanded all artillery on Iwo Jima.

Typical of the thoroughness employed in the construction of subterranean defenses was the main communications center south of Kita village, which was so spacious that it contained a chamber 50 m long and 20 m wide.

Initially, Colonel Nishi had planned to employ his armor as a type of "roving fire brigade", to be committed at focal points of combat.

While Iwo Jima was being converted into a major fortress with all possible speed, General Kuribayashi formulated his final plans for the defense of the island.

During the final months of preparing Iwo Jima for the defense, General Kuribayashi saw to it that the strenuous work of building fortifications did not interfere with the training of units.

In an operations order issued in early December, the island commander set 11 February 1945 as the target date for completion of defensive preparations and specified that personnel were to spend 70% of their time in training and 30% in construction work.

General Kuribayashi made several changes in his basic defense plan in the months preceding the American invasion of Iwo Jima.

On the other hand, this entire area was exposed to the fire of artillery, rocket launchers, and mortars emplaced on Suribachi to the south and the high ground to the north.

Colonel Nishi's immobilized tanks, carefully dug in and camouflaged, further reinforced this fortified area, whose strength was supplemented by the broken terrain.

As an additional means of protecting the two completed airfields on Iwo from direct assault, the Japanese constructed a number of antitank ditches near the fields and mined all natural routes of approach.

Even though frequent air raids interfered with the Japanese defensive preparations and robbed the garrison of badly needed sleep, work was not materially slowed.

As early as 5 January 1945, Admiral Ichimaru conducted a briefing of naval personnel at his command post in which he informed them of the destruction of the Japanese Fleet at the Battle of Leyte Gulf, the loss of the Philippines, and the expectation that Iwo would shortly be invaded.

Exactly one month later, Japanese radio operators on Iwo reported to the island commander that code signals of American aircraft had undergone an ominous change.

The potential for interservice rivalry between the Army and Navy created by this partition of responsibility was exacerbated by similar divisions within the Joint Chiefs of Staff (JCS) in Washington.

Seeking to gain leverage and so break the impasse, on 29 September Nimitz suggested to Admiral Ernest King that as a preliminary to the Okinawa offensive the island of Iwo Jima could be taken.

[1] The tiny island lacked harbors and so was of no direct interest to the Navy, but for some time General Henry Harley Arnold of the U.S. Army Air Forces had been lobbying to take Iwo Jima.

He argued that an airbase there would provide useful fighter escort cover for the B-29 Superfortresses of his XX Bomber Command, then beginning its strategic bombing campaign against the Japanese home islands (the later role of Iwo Jima as a refueling station for B-29s played no part in the original decision-making process).

"[3] On 9 October, General Holland Smith received the staff study, accompanied by a directive from Admiral Nimitz ordering the seizure of Iwo Jima.

When released to VAC, the 3rd Marine Division, as Expeditionary Troops Reserve, was to land over the same beaches to take part in the attack or play a defensive role, whichever was called for.

Action by the 27th and 28th Marines was designed to drive the enemy from the commanding heights along the southern portion of Iwo, simultaneously securing the flanks and rear of VAC.

However, since predominant northerly or northwesterly winds caused hazardous swells almost continuously along the southwest side of the island, it appeared unlikely that this alternative plan would be put into effect.