Battle of Iwo Jima
Japanese Defense

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Battle of Iwo Jima
Iwo Jima Battle Ships
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Iwo Jima Battle Assault Ship LPH-2 Operations
Battle of Iwo Jima - American Landing

Conflict: WW2 World War II, Pacific War
Date: February 16, 1945 – March 26, 1945
Place: Iwo Jima, Japan
Outcome: American victory
Combatants
United States Japan
Commanders
Holland Smith Tadamichi Kuribayashi
Strength
70,000 22,000
Casualties
7,000 dead,
19,000 wounded
21,800 dead,
200 POW
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Battle of Iwo Jima - Japanese Defense
Tadamichi Kuribayashi, commander of the Japanese garrison defending Iwo JimaEven before the fall of Saipan in June 1944, Japanese planners knew that Iwo Jima would have to be reinforced materially if it were to the held for any length of time, and preparations were made to send sizable numbers of men and quantities of materiel to that island. In late May, Lieutenant General Tadamichi Kuribayashi was summoned to the office of the Prime Minister, General Hideki Tojo, who informed the general that he had been chosen to defend Iwo Jima to the last. Kuribayashi was further apprised of the importance of this assignment when Tojo pointed out that the eyes of the entire nation were focused on the defense of Iwo. Fully aware of the implications of the task entrusted to him, the general accepted. By 8 June 1944, Kuribayashi was on his way to his toughest and final assignment, determined to convert Iwo Jima into an invincible fortress that would withstand any type of attack from any quarter.

When he arrived, some 80 fighter aircraft were stationed on Iwo Jima, but by early July there were just four left. A United States Navy force boldly appeared within sight of the island and subjected the Japanese to a naval bombardment from point-blank range over two days. This shelling destroyed every building on the island and smashed the four remaining aircraft.

Much to the surprise of the Japanese garrison on Iwo, an American invasion of the island did not materialize during the summer of 1944. There was little doubt that in time the Americans would be compelled to attack the island. General Kuribayashi was more determined than ever to exact the heaviest possible price for Iwo when the invaders came. Without naval and air support, it was a foregone conclusion that Iwo could not hold out indefinitely against an invader possessing both naval and air supremacy.

Battle of Iwo Jima - Emplacement of Artillery
As a first step in readying Iwo for a prolonged defense, the island commander ordered the evacuation of all civilians from the island. This was accomplished by late July. Next came an overall plan for defense of the island. Lieutenant General Hideyoshi Obata, Commanding General of the Thirty-First Army, early in 1944 had been responsible for the defense of Iwo prior to his return to the Marianas. At the time, faithful to the doctrine that an invasion had to be met practically at the water's edge, Obata had ordered the emplacement of artillery and the construction of pillboxes near the beaches. General Kuribayashi had different ideas. Instead of a futile effort to hold the beaches, he planned to defend the latter with a sprinkling of automatic weapons and infantry. Artillery, mortars, and rockets would be emplaced on the foot and slopes of Mount Suribachi, as well as in the high ground to the north of Chidori airfield.

A prolonged defense of the island required the preparation of an extensive system of caves and tunnels, for the naval bombardment had clearly shown that surface installations could not withstand extensive shelling. 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.

On 10 August 1944, Rear Admiral Toshinosuka Ichimaru reached Iwo, shortly followed by 2,216 naval personnel, including naval aviators and ground crews. 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.

Next to arrive on Iwo were artillery units and five antitank battalions. Even though numerous supply ships on route to Iwo Jima were sunk by American submarines and aircraft, substantial quantities of materiel did reach Iwo during the summer and autumn of 1944. By the end of the year, 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 defenses could boast of more than two hundred 20 mm and 25 mm antiaircraft guns and 69 37 mm and 47 mm antitank guns.

Initially, Colonel Nishi had planned to employ his armor as a type of "roving fire brigade", to be committed at focal points of combat. The rugged terrain precluded such employment and in the end, under the colonel's watchful eyes, the tanks were deployed in static positions. They were either buried or their turrets were dismounted and so skillfully emplaced in the rocky ground that they were practically invisible from the air or from the ground.

Battle of Iwo Jima - Fortifications
For the remainder of 1944, the construction of fortifications on Iwo also went into high gear. 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. Pillboxes near the beaches north of Mount Suribachi were constructed of reinforced concrete, many of them with walls four feet thick. At the same time, an elaborate system of caves, concrete blockhouses, and pillboxes was established. One of the results of American air attacks and naval bombardment in the early summer of 1944 had been to drive the Japanese so deep underground that eventually their defenses became virtually immune to air or naval bombardment.

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 developed it into a science. Because of the importance of the underground positions, 25 percent of the garrison was detailed to tunneling. Positions constructed underground ranged in size from small caves for a few men to several underground chambers capable of holding 300 or 400 men. 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. Special attention had to be paid to providing adequate ventilation, since sulphur fumes were present in many of the underground installations. Fortunately for the Japanese, most of the volcanic stone on Iwo was so soft that it could be cut with hand tools.

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. This installation, 20 m underground, consisted of caves of varying sizes, connected by 150 m of tunnels. Here the island commander had his own warroom in one of three small concrete enclosed chambers; the two similar rooms were used by the staff. Farther south on Hill 382, the second highest elevation on the island, the Japanese constructed a radio and weather station. Nearby, on an elevation just southeast of the station, an enormously large blockhouse was constructed which served as the headquarters of Colonel Chosaku Kaido, who commanded all artillery on Iwo Jima. Other hills in the northern portion of the island were tunnelled out, All of these major excavations featured multiple entrances and exits and were virtually invulnerable to damage from artillery or aerial bombardment. 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.

Perhaps the most ambitious construction project to get under way was the creation of an underground passageway designed to link all major defense installations on the island. As projected, this passageway was to have attained a total length of almost 17 miles (27 km). Had it been completed, it would have linked the formidable underground installations in the northern portion of Iwo Jima with the southern part of the island, where the northern slope of Mount Suribachi alone harbored several thousand yards of tunnels. By the time the Marines landed on Iwo Jima, more than 11 miles (18 km) of tunnels had been completed.

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. This plan, which constituted a radical departure from the defensive tactics used by the Japanese earlier in the war, provided for the following major points:

In order to prevent disclosing their positions to the Americans, Japanese artillery was to remain silent during the expected prelanding bombardment. No fire would be directed against the American naval vessels.
Upon landing on Iwo Jima, the Americans were not to encounter any opposition on the beaches.

Battle of Iwo Jima - Motoyama airfield
Once the Americans had advanced about 500 m inland, they were to be taken under the concentrated fire of automatic weapons stationed in the vicinity of Motoyama airfield to the north, as well as automatic weapons and artillery emplaced both on the high ground to the north of the landing beaches and Mount Suribachi to the south.
After inflicting maximum possible casualties and damage on the landing force, the artillery was to displace northward from the high ground near the Chidori airfield.
In this connection, Kuribayashi stressed once again that he planned to conduct an elastic defense designed to wear down the invasion force. Such prolonged resistance naturally required the defending force to stockpile rations and ammunition. To this end the island commander accumulated a food reserve to last for two and a half months, ever mindful of the fact that the trickle of supplies that was reaching Iwo Jima during the latter part of 1944 would cease altogether once the island was surrounded by a hostile naval force.

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. As an initial step towards obtaining more time for training, he ordered work on the northernmost airfield on the island halted.

Despite intermittent harassment by American submarines and aircraft, additional personnel continued to arrive on Iwo until February 1945. By that time General Kuribayashi had under his command a force totalling between 21,000 and 23,000 men, including both Army and Navy units.

General Kuribayashi made several changes in his basic defense plan in the months preceding the American invasion of Iwo Jima. The final stratagem, which became effective in January 1945, called for the creation of strong, mutually supporting positions which were to be defended to the death. Neither large scale counterattacks, withdrawals, nor banzai charges were contemplated. The southern portion of Iwo in the proximity of Mount Suribachi was organized into a semi-independent defense sector. Fortifications included casemated coast artillery and automatic weapons in mutually supporting pillboxes. The narrow isthmus to the north of Suribachi was to be defended by a small infantry force. 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.

Battle of Iwo Jima - Antitank Ditches
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. When, on 2 January, more than a dozen B-24 Liberator bombers raided Airfield No. 1 and inflicted heavy damage, Kuribayashi diverted more than 600 men, 11 trucks, and 2 bulldozers for immediate repairs. As a result, the airfield again became operational after only 12 hours. Eventually, 2,000 men were assigned the job of filling the bomb craters with as many as 50 men detailed to each bomb crater.

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. On 13 February, a Japanese naval patrol plane spotted 170 American ships moving northwestward from Saipan. All Japanese troops in the Ogasawaras were alerted and occupied their battle positions. On Iwo Jima, preparations for the pending battle had been completed, and the defenders were ready.

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Battle of Iwo Jima - Japanese Defense