Historical Background

Strategic Planning

As early as September 1943 the Joint War Planning Committee met in Washington to discuss plans for the campaign against the Japanese homeland. The Central Pacific Forces had first to neutralise the Caroline Islands so that new sea and air bases could be established; only then could attacks be launched against the Japanese Navy. The Army Air Force also wanted air bases on the Mariana Islands so their new long-range B-29 Superfortress bombers could start bombing mainland Japan.

The Committee identified the capture of one of the Nanpo Islands, midway between the Marianas and Tokyo, as an objective for early 1945. The islands were a vital part of the Japanese outer defences and the largest island in the Volcano Island group, Iwo Jima, was singled out as a key objective. Long-range fighters could then use the island’s airfields to escort the bombers to Japan; returning damaged bombers could also land on the island.

In March 1944 the invasion of the Marianas was scheduled for 15 June and it would be the first stage in the advance towards the Japanese homeland.

At the end of June a paper entitled ‘Operations Against Japan Subsequent to Formosa’ proposed advancing from the Mariana Islands to the Nanpo Islands in April 1945. On 12 August the Joint War Planning Committee submitted an outline plan for the invasion of Iwo Jima to the Joint Staff Planners. It listed the following advantages of taking the island:

1.   It would take a strategic outpost from the Japanese.

2.   Fighter planes could provide air cover for the new bases on the Marianas.

3.   Fighter planes would also provide protection for bombers heading for Japan.

4.   Bombers could use the island for staging attacks on Japan.

The US Armed Forces continued their operations across the Pacific throughout the summer of 1944. Saipan, Tinian and Guam were taken, clearing the Marianas by the end of August. While the Japanese Navy Air Service suffered heavily, the US Air Force went from strength to strength as new air bases were built. The continued successes convinced the US High Command that they could take any island in the Pacific if sufficient naval, amphibious and shore-based air forces were made available. It meant that an attack on Iwo Jima had become a case of when, not if.

The Pacific War at the end of 1944 involved simultaneous attacks on the Philippine Islands and the Marianas Islands.

Joint Staff Planners presented the Joint Logistics Committee with its plans for the invasion of Iwo Jima by September, asking for three divisions to be ready for 15 April 1945. Admiral Chester W. Nimitz told Lieutenant General Holland M. Smith, Commanding General of the Fleet Marine Force, Pacific, to keep the 2nd and 3rd Marine Divisions ready in the Marianas as a reserve for the invasion of Formosa; they would then be used to attack Iwo Jima.

However, the Navy, Army, and Army Air Force commanders were all reconsidering the need for the invasion of Formosa. Admiral Nimitz had originally wanted bases in Formosa ready to strike the Chinese coast but recent Japanese gains in the area made him change his mind. Meanwhile, both Lieutenant General Robert C. Richardson Jr, Commanding General, Army Forces, Pacific Ocean Areas, and Lieutenant General Millard F. Harmon, Commanding General of the Army Air Forces, Pacific Ocean Areas, wanted to strike Iwo Jima instead of Formosa.

Admiral Nimitz, Admiral Ernest J. King (Commander, US Navy and Navy member of the Joint Chiefs of Staff), Admiral Raymond A. Spruance (Commander, US Fifth Fleet) and Lieutenant General Simon B. Buckner (Tenth US Army Commander and Commander of the Formosa Landing Force) met late in September in San Francisco to make the decision. The meeting illustrated that there were insufficient troops for the Formosa and southeast China operations. The War Department was also refusing to increase troop numbers in the Pacific until the war in Europe was over. Instead, Admiral King explained that there were enough forces for a different strategy. Iwo Jima in the Nanpo Islands would be taken first in January 1945; fighter support could then be provided for the B-29s raiding Tokyo. The capture of Okinawa Island in the Nansei Islands (also called Ryukyu Islands) would provide a staging area for the invasion of the Japanese mainland.

Admiral King returned to Washington and the Joint Chiefs of Staff approved the change in strategy. They issued a new directive to Admiral Nimitz in which he was told to prepare for the following operations:

1.   Provide fleet cover and support for the attack on Luzon; target date 20 December 1944.

2.   Occupy one or more of the Nanpo Islands; target date 20 January 1945.

3.   Occupy one or more of the Nansei Islands, target date 1 March 1945.

On 9 October 1944 Admiral Nimitz told General Holland M. Smith (nicknamed ‘Howling Mad’), to prepare for an invasion of Iwo Jima.

The Joint War Plans Committee issued a paper called ‘Operations for the Defeat of Japan’ on 18 October outlining the advantages of capturing Iwo Jima:

1.   It would establish sea and air blockades.

2.   It would allow B-29 bombers to carry out air attacks on the Japanese mainland.

3.   It would contribute to the destruction of Japanese naval and air power.

4.   It would pave the way for the eventual invasion of Japan.

Planning for the invasion of Iwo Jima could now begin in earnest.

Iwo Jima was in the Nanpo Shoto Islands, south of Japan. It was also halfway between the airbases in the Marianas Islands and Tokyo.

Airbases on the Marianas become operational in November 1944 and B-29 bombers immediately began bombing mainland Japan, in particular the capital, Tokyo. News of the raids gave the American people and servicemen a morale boost but plane and crew losses were high, far too high. If a plane was damaged by enemy action over Japan or suffered a malfunction, the crew had to ditch in the Pacific Ocean where their chances of being rescued were zero. Although the raids had to continue, the US Air Force was desperate for a staging airfield along the flight route, and Iwo Jima was the place. Not only could fighter squadrons join the bombers en route to Tokyo, crippled bombers could land on it.

Operational Planning

Planning for Iwo Jima continued throughout October but by mid-November it was clear that the timetable of operations had to be changed. The interval between the invasion of Luzon on 20 December and Iwo Jima on 20 January did not give time to switch shipping from one area to the other. Admiral Nimitz recommended delaying the attack on Iwo Jima (Operation Detachment) to 3 February while the invasion of Okinawa (Operation Iceberg) was rescheduled for 15 March.

The campaign to clear Leyte in the Philippines was also taking far longer than expected owing to the arrival of two new Japanese divisions on the island and the atrocious weather. General Douglas MacArthur, Supreme Commander of the Southwest Pacific Area,had to postpone the assault on Luzon to 9 January 1945, in turn delaying the invasion of Iwo Jima. At the beginning of December Admiral Nimitz recommended delaying Operations Detachment and Iceberg to 19 February and 1 April 1945 respectively; the Joint Chiefs agreed.

Troops and equipment come ashore on Luzon Island, the largest of the Philippine Islands. (NARA-111-SC-200008)

Planning Operation Detachment

Admiral Nimitz’s staff published a preliminary report of the invasion of Iwo Jima on 7 October so planning could begin. Operation Detachment’s objectives were to extend US armed forces control over the Western Pacific while maintaining military pressure against Japan. The capture of the island and its airbases were also outlined as part of the overall strategy for the defeat of Japan. Admiral Nimitz’s directive also specified the four commanders for the operation:

1   Operation: Commander Admiral Raymond A. Spruance, USN.

2   Joint Expeditionary Force: Commander Vice Admiral Richmond Kelly Turner, USN.

3   Joint Expeditionary Force Second in Command: Rear Admiral Harry W. Hill, USN.

4   Expeditionary Troops Commander: Lieutenant General Holland M. Smith, USMC.

General Smith received Admiral Nimitz’s directive on 9 October and his staff immediately set to work planning the invasion. Fifth Fleet and V Amphibious Corps had cooperated before during the capture of the Gilberts, the Marshalls and the Marianas, and all levels of staff were used to working together. Responsibilities were distributed as follows:

Major General Harry Schmidt, commander of V Amphibious Corps, was in turn appointed Commanding General of the Landing Force. Schmidt’s staff were responsible for preparing the Marine aspect of invasion, knowing that they had the Headquarters, Fleet Marine Force, Pacific, at their disposal.

3rd, 4th and 5th Marine Divisions had been assigned as V Amphibious Corps’ Landing Force. 3rd Division had just captured Guam and it was resting and refitting on the island. 4th Division had just taken Saipan and Tinian and it was resting and refitting at its base on Maui in the Hawaiian Islands. Iwo Jima would be 5th Division’s first battle but many combat-experienced troops had been transferred to it to help it complete training on Hawaii Island.

V Amphibious Corps Headquarters moved to Pearl Harbor on Oahu Island, in the Hawaii chain on 13 October 1944 to facilitate planning, and six days later Schmidt issued an outline plan. The following day, General Holland Smith, the Commanding General of Fleet Marine Force, Pacific, issued troop assignments to General Schmidt.

As the various staffs worked together to finalise the planning for the invasion of Iwo Jima, Schimdt’s original plan evolved to accommodate information gathered from aerial intelligence reports. The various headquarters published their final drafts for Operation Detachment on the following dates:

By the time Admiral Spruance assumed command of all forces assigned to Central Pacific Task Force on 26 January 1945, all elements of Operation Plan 11-44 were being developed.

As V Amphibious Corps made its final preparations for Iwo Jima, Sixth Army was advancing across Luzon. Huge plumes of smoke rise above Manila’s docks as the battle for the city begins. (NARA-111-SC-200052)