World War Two: Marianas (2-3) Planning the Invasion-Saipan &Guam

For the Marianas, as in the case of all operations in the Pacific outside of General MacArthur’s jurisdiction, Admiral Nimitz retained over-all command of the campaign. Under him in the chain of command was Vice Admiral Raymond A. Spruance, commander of the Fifth Fleet, and under him Vice Admiral Richmond Kelly Turner, who was to command the Joint Expeditionary Force (Task Force 51), was charged with the actual job of taking the islands. Turner wore a second hat. Until 15 July 1944, he was also in command of the Northern Attack Force (Task Force 52), which was made up of all the amphibious elements assigned to the attack on Saipan and Tinian, and which was one of the two component parts of Task Force 51. Its equivalent for Guam was designated Southern Attack Force (Task Force 53) and was commanded by Rear Admiral Richard L. Conolly. Vice Admiral Marc A. Mitscher’s Fast Carrier Task Force (Task Force 58) and Vice Admiral Charles A. Lockwood’s Submarine Force, Pacific Fleet (Task Force 17), were assigned supporting missions according to their appropriate capacities. The former operated as part of the Fifth Fleet and the latter directly under Admiral Nimitz.

Tactical command of all troops ashore for the Marianas operation devolved upon Lieutenant General Holland M. Smith, USMC. General Smith was perhaps as well grounded in the fundamentals of amphibious techniques as any general officer in either the Army or the Marine Corps at that time.

In 1941 and 1942 he had supervised the training of the 1st Infantry Division and the 1st Marine Division in basic landing problems on the U.S. east coast. At that time amphibious warfare was still something of a novelty, and United States forces were generally innocent of the fundamentals of launching an assault of seaborne troops against a hostile shore.

For at least two decades before the outbreak of World War II, it is true, the Marine Corps had slowly been piecing together a workable body of amphibious doctrine, and after 1934, in conjunction with the U.S. Navy, it had conducted yearly landing exercises, chiefly on the island of Culebra, Puerto Rico. These had been valuable, indeed indispensable, experiments. They were in no small measure responsible for the ability of American troops to invade the beaches of Africa, Europe, and countless Pacific islands. Not until after the fall of France did the United States commence to prepare in earnest for large-scale amphibious landings.

In February of 1941 General Smith and his staff planned and oversaw a joint Army-Marine Corps practice landing in the Culebra area. In June of the same year the first full two-division landing exercise was conducted at New River, North Carolina, under their supervision. Another was held on a somewhat smaller scale off Lynn Haven Roads, Virginia, in January of 1942, Two months later, General Smith was ordered to duty as Commander, Amphibious Corps, Atlantic Fleet, an amphibious training command, and later in the year he served in much the same capacity as Commanding General, Amphibious Corps, Pacific Fleet. In September 1943 he and his staff left San Diego for the Central Pacific, where Smith was to be commander of the V Amphibious Corps. As such, he commanded the expeditionary troops that captured Tarawa and Makin in the Gilbert Islands and Kwajalein and Eniwetok in the Marshalls. Now his task was even greater. Holland Smith’s designation for this operation was Commanding General, Expeditionary Troops (Task Force 56). He was directly responsible to Admiral Turner until the amphibious phase was completed.

Like Turner, he was to play a dual role. As Commander, Northern Troops and Landing Force (Task Group 56.1), he personally exercised tactical control of all troops ashore during the capture of Saipan. He was relieved on 12 July 1944 from this command (but not from command of Expeditionary Troops) by Major General Harry Schmidt, USMC, who thereafter performed the same role during the seizure of Tinian. Their counterpart on Guam was Major General Roy S. Geiger, USMC, the commanding general of III Amphibious Corps and of Southern Troops and Landing Force (Task Group 56.2). Although in this capacity Geiger and Smith held parallel commands, the former was subordinate to the latter as Commanding General, Expeditionary Troops.

The command relationships among General Smith, his naval superiors, and his Marine and Army subordinates, although resembling in complexity the hierarchy of saints, can be reduced to fairly simple terms. In effect Admiral Spruance enjoyed, by delegation from Admiral Nimitz, supreme command of the operation. He retained operational command throughout and upon him devolved the responsibility of determining when the capture and occupation phase of each island had been completed. Tactical command during the amphibious phases of the operation was placed in the hands of Admiral Turner, who exercised it directly at Saipan and through Rear Admiral Harry W. Hill on Tinian and Admiral Conolly on Guam. The completion of the amphibious phase was determined in each instance by the landing force commander—whenever he decided that the situation warranted it, he was to establish his command ashore.

Thereafter, all tactical decisions regarding the disposition of troops would be made by him. On Saipan the landing force commander was Holland Smith, on Tinian Harry Schmidt, and on Guam Roy S. Geiger. On all three islands, however, “overall troop command” was retained by General Smith as Commander, Expeditionary Troops.

There were 105,859 assault troops assigned to capture the three islands; 66,779 were allocated to Saipan and Tinian and the remaining 39,080 to Guam. The bulk of the force was made up of two reinforced Army divisions, three reinforced Marine divisions, and a provisional Marine brigade consisting of two regimental combat teams.

The landing on Saipan was to be made by the ad and 4th Marine Divisions, with the 27th Infantry Division in reserve, All three of these organizations had seen previous action in the Pacific. The 2nd Marine Division was activated in San Diego on 1 February 1941. One regiment (2nd Marines) took part in the initial attack on Guadalcanal on 7 August 1942, and the remaining two entered that campaign in November and January, The division had also fought the bloody battle of Tarawa, losing over 3,000 casualties there. An independent Marine unit, the 1st Battalion, 29th Marines, which was formed in the spring of 1944 around cadres of 2nd Marine Division veterans of Guadalcanal and Tarawa, was attached to the 2nd Division for the Saipan operation. In the Marianas, the division was commanded by Major General Thomas E. Watson, USMC, who had previously led the Marine and Army regimental combat teams that captured Eniwetok in the Marshalls.

The 4th Marine Division was not formally activated until 16 August 1943, but it was by no means totally unseasoned. In early February 1944 it had captured Roi and Namur Islands in Kwajalein Atoll while troops of the 7th Infantry Division were taking nearby Kwajalein Island in the central Marshalls.9 The 4th was to be commanded at Saipan by General Schmidt, who had been the division’s commander since it was first formed. When General Schmidt relieved Holland Smith of command of the Northern Troops and Landing Force after Saipan was officially declared secure, he in turn was succeeded in command of the 4th Marine Division by Major General Clifton B. Cates, a veteran of Guadalcanal and an alumnus of the 1st Marine Division.

The 27th Infantry Division was a National Guard unit of New York State when it was called into federal service in October 1940. Its three regiments, the 105th, 106th, and 165th, had had their headquarters at Troy, Albany, and New York City, respectively. It was the first combat division to leave the United States for Pacific duty and by the war’s end had spent a longer time overseas than any National Guard division in the United States Army.

In March 1942 advance echelons arrived in Hawaii and for the next year and a half the division served as base defense force, first for the outer islands and then on Oahu after the 25th Division was sent to Guadalcanal. In November 1943 the 165th Infantry, reinforced by the 3rd Battalion, 105th Infantry plus organic artillery, engineer, and service units, invaded and captured Makin simultaneously with the 2nd Marine Division’s assault on Tarawa.

Three months later two battalions (1st and 3rd) of the 106th Infantry, plus an independent Marine regiment, took Eniwetok Atoll. Thus, of the entire 27th Division only the 1st and 2nd Battalions, 105th Infantry, and 2nd Battalion, 106th, which secured Majuro Atoll without battle, were unseasoned in atoll warfare.

Major General Ralph C. Smith joined the 27th Division as commanding general in November 1942. His previous wartime duty had been with the Military Intelligence Division (G-2) of the War Department General Staff and with the 76th Infantry Division at Fort George G. Meade. His primary job for the next year was to supervise training of the division for forthcoming operations. His own initiation into Pacific warfare came at Makin, where he exercised tactical command over the reinforced 165th Infantry Regiment.

Aside from the three reinforced infantry divisions, the largest single unit attached to Northern Troops and Landing Force for the Marianas operation was the XXIV Corps Artillery (Army). The organization was formally activated on 25 March 1944 and consisted of two battalions each of 155-mm. howitzers and 155-mm. guns.

The nucleus of this new organization consisted of coastal artillery and field artillery battalions originally assigned to the defense of Oahu. One battalion (145th) had participated in the Kwajalein Island landing, but the rest were new to combat. For the Marianas Campaign the corps artillery was commanded by Brig. General Arthur M. Harper, a field artilleryman since 1920. Between the commencement of the war and his assignment to XXIV Corps, he had served as artillery officer of I Corps, of the 30th Infantry Division, and as commanding general of III Corps Artillery. The 22nd Marines. This unit later was incorporated into the 1st Marine Provisional Brigade, which fought on Guam. The brigade was subsequently expanded to the 6th Marine Division, which saw action on Okinawa.

Major General Ralph C. Smith at Tactical Planning Headquarters, V Amphibious Corps, was first alerted to its forthcoming responsibilities in the Marianas on 15 January 1944, when it received Admiral Nimitz’ Campaign Plan GRANITE setting forth the concept and outlining a tentative schedule of operations for the Central Pacific area for the year 1944. Operation FORAGER, involving the seizure, occupation, and defense of Saipan, Tinian, and Guam, was included as the final phase of this program. The first two months of 1944 witnessed an unexpected speed-up in Pacific operations.

By 17 February, as already noted, Kwajalein Atoll had been seized, a successful landing had been made on Eniwetok, and, most important, a fast carrier strike against Truk had revealed the alleged impregnability of that once-powerful base to be a myth, On 13 March, therefore, Nimitz assigned highest priority to the Marianas operation.

A week later he issued his Joint Staff Study for FORAGER to all major commanders as a guide for advanced planning. The study indicated that V Amphibious Corps, including the 2nd and 4th Marine Divisions, would be mounted in the Hawaiian area for the initial assault on the beaches of Saipan with the 27th Infantry Division in reserve. The III Amphibious Corps, consisting of the 3rd Marine Division and the 1st Provisional Marine Brigade, was to be mounted in the Guadalcanal area for an invasion of Guam. The 77th Infantry Division was to be alerted in the Hawaiian area for possible movement to the Marianas twenty days after the initial landing on Saipan. The probable target day (D Day) for Saipan was set as 15 June. The date for the invasion of Guam (W Day) was tentatively established as 18 June.

On 12 April General Holland Smith divided his V Amphibious Corps staff into two separate components. One, initially known as the Red Staff, later functioned as Northern Troops and Landing Force (Task Group 56.1) for the capture of Saipan and Tinian. The other portion, first known as Blue Staff, later served as Headquarters Expeditionary Troops (Task Force 56).19 General Smith’s two staffs were heavily augmented by U.S. Army personnel. On the Northern Troops and Landing Force Staff, the assistant chiefs of staff for both intelligence (G-2) and supply (G-4) were Army officers—Lieutenant Colonel Thomas R. Yancey and Lieutenant Colonel Joseph C. Anderson.

There were disadvantages to this cellular fission, however unavoidable it may have been. First, there was a decided shortage of trained personnel, especially of special staff sections, officer assistants and trained clerks, draftsmen, and stenographers; and second, a shortage of headquarters and corps troops already existed in V Amphibious Corps. “In effect,” as one commentator put it, “you have here an army and a corps trying to operate with a staff too small for a corps,” All echelons prepared their plans simultaneously, and the normal time sequence of planning from highest echelon down, with each subordinate basing his own plan on that of his immediate superior, was seldom achieved. For example, Headquarters Expeditionary Troops (Task Force 56) Operation Plan 3-44 was issued on 26 April, whereas the next higher echelon, Admiral Turner’s Headquarters Northern Attack Force (Task Force 52) did not issue its plan until 21 May. Again, it was not until 12 May that Admiral Spruance, who was superior to both Turner and Smith, came out with his operation plan for the Fifth Fleet.

Northern Troops and Landing Force

Headquarters Operation Plan 3-44 of 1 May summarized all previous plans from higher echelons and governed the tactical order of all troops in the proposed landings on Saipan.24 The 4th Marine Division (reinforced) was to land on Blue and Yellow Beaches, extending from the town of Charan Kanoa south almost to Agingan Point. Its first objective was to be a line inland from the beaches about 2,000 yards at the north and tapering down to the water’s edge at the southern end. Then, on order, the division was to advance rapidly and seize Aslito airfield and the surrounding terrain.

The 2nd Marine Division was to land simultaneously to the north of Charan Kanoa on Green and Red Beaches, seize the first commanding ground inland, and then advance rapidly and capture Mount Tapotchau and Mount Tipo Pale and the adjacent ground. The XXIV Corps Artillery was to land on order on beaches to be designated and to execute missions as assigned. North of the 2nd Marine Division’s beaches, in the vicinity of Tanapag Harbor, a naval force consisting of transport divisions carrying reserve regiments from the 2nd and 4th Marine Divisions would conduct a diversionary demonstration to last from a half hour before sunrise to an hour after the main landing.

Finally, the 1st Battalion, 2nd Marines, was detached from its parent organization to perform a separate mission. Originally, the battalion was to land from destroyer transports (APD’s) on Magicienne Bay on the southeast side of the island the night before the main landing on the west coast.

It would then move rapidly inland, attempt to seize Mount Tapotchau before daylight and hold on until relieved by the main elements of the 2nd Marine Division, Later, on 7 May, this order was changed, and the battalion was to be prepared to land on Magicienne Bay or perhaps other beaches after the main landing had been effected and then move west and north to attack enemy positions from the rear. Eventually, the whole scheme was canceled as impractical and involving excessive risks.

The final decision was in all probability the soundest one. To have committed a single battalion armed with nothing heavier than 60-mm. mortars against the formidable defenses the Japanese had set up around Magicienne Bay would in all likelihood have proved disastrous. As events turned out, it took the entire 2nd Marine Division ten days to reach Mount Tapotchau’s summit.

At headquarters of the 27th Division the problem of planning for landings on Saipan was seriously complicated because there was no certainty as to how the division would be employed. It was the corps reserve and might be committed on Saipan only in part or piecemeal, might be reserved for later action on Tinian and Guam, or might not be used at all. In short, there were a large number and wide variety of possibilities, and operations officers had to plan accordingly. Hence, Ralph Smith’s G-3 (operations) section found it necessary to prepare a total of twenty-one complete plans for tactical employment of the division. A few of these were discarded as higher headquarters made progress in outlining the details of their own plans. By the time the troops sailed from Hawaii it appeared that, if used on Saipan at all, the division would probably be employed in one of three ways and, accordingly, three preferred plans were devised. The first contemplated a landing of two regiments (105th and 165th) on beaches at Magicienne Bay and a rapid advance northwest across the island to capture the seaplane base at Flores Point, The second envisaged a landing by the same two regiments on the beaches north of Charan Kanoa, on the left of the 2nd Marine Division, followed by a northward thrust to Garapan Village. If either of these were executed, the third regiment (106th Infantry) would act as floating reserve. Plan number three called for the two assault regiments to go ashore at Tanapag Harbor and prepare to move southward to join forces with the 2nd Marine Division. In this case, the 106th Regimental Combat Team (RCT) was to seize Maniagassa Island off Tanapag and support the main assaut A final plan was made only after the division had sailed from Hawaii. On its arrival at Kwajalein the 106th Infantry was attached to the Southern Landing Force and ordered to prepare plans for a landing on Guam.

In actual fact, all of the plans had to be abandoned early in the battle for Saipan. Although it cannot be said that all the laborious preparations by the 27th Division were entirely wasted, it is true that neither the division nor the corps headquarters had on hand a detailed plan that exactly fitted the situation as it had developed by the time the division was committed.

Preliminary naval and aerial bombardment of the Marianas was planned along lines by then well established in the Central Pacific theater. Landings at Tarawa and in the Marshalls left little doubt of the necessity for heavy preliminary pounding of the beaches from both the air and the sea if excessive American casualties were to be avoided.

For Saipan, an impressive armada of ships and planes was allocated to do the job. A total of fifty-five ships was originally scheduled to deliver fire against the main island: 7 fast battleships from Marc Mitscher’s fast carrier force, 4 old battleships, 2 heavy cruisers, 3 light cruisers, 15 destroyers, and 24 LCI gunboats (LCI (G)’s). Simultaneously with this bombardment, the smaller island of Tinian was to be subjected to similar fire from an additional 33 ships, including 3 old battleships, 4 heavy cruisers, 2 light cruisers, 7 destroyers, and 24 LCI(G)’s.

Two days before the scheduled landing, fast battleships and destroyers of Task Force 58 were to bombard Saipan and Tinian, destroy aircraft, put airfields out of commission, destroy coast defense and antiaircraft batteries, burn off cane fields in the landing area, deliver antipersonnel fire, and, finally, cover mine-sweeping operations off the western shore line. Next day, old battleships and smaller fire support ships of Turner’s Task Force 52 were scheduled to deliver counterbattery fire, area bombardment, and interdiction fire, commencing at daybreak and continuing throughout the day. Their primary mission was to destroy as many coast defense guns, antiaircraft batteries, artillery weapons, and other enemy defenses and personnel as possible. Ships were directed to remain well beyond the range of enemy shore batteries on that day, which meant in effect that their fire would be delivered at ranges in excess of 10,000 yards.31 They were instructed to pay particular attention to gun positions at Magicienne Bay and to the beach defenses and installations on the selected landing beaches on the west coast.

Also, they were to cover mine-sweeping operations and beach reconnaissance by the underwater demolition teams, whose job it was to inspect the beaches and approaches thereto for mines, underwater obstacles, and explosives. Simultaneously, ships of Admiral Conolly’s Task Force 53 were to work over neighboring Tinian in much the same manner, although these vessels were to conserve most (80 percent) of their ammunition allowance for pre-assault bombardment of Guam.

For D Day (15 June) on Saipan the schedule of fires was to be stepped up sharply, with particular attention to be paid to the landing beaches. Counterbattery fire was to commence at dawn and to cover known and suspected positions of enemy coast defense guns and antiaircraft, dual-purpose, and field artillery batteries both on Saipan and on Tinian. Ships were to be in position to bombard beach defenses and possible flanking positions, with close-range fire to commence at the low-water line and extend 400 yards inland. Area bombardment of secondary defenses such as supply installations, barracks, and bivouac areas was to be continued, as was supporting bombardment of Tinian by Task Force 53. Shortly before the scheduled landing hour (H Hour) on Saipan, close supporting fires were to be delivered against the Charan Kanoa beaches and in the Tanapag Harbor area, the latter being in support of the demonstration landing and therefore on a smaller scale. All naval gunfire, except for counterbattery fire necessary to the protection of ships and landing craft, was to cease for a half hour (between H minus 90 and H minus 60) to permit a low-altitude aerial strike on the beaches, and then resume for the hour before the landing. For the hour remaining before the troops were scheduled to touch shore, battleships, cruisers, and destroyers were directed to move in to close range and bombard the selected landing beaches and adjacent installations.

Then, just before the scheduled landing hour, when the assault troops were assembled in the leading waves of amphibian tractors, twenty-four LCI gunboats, equipped with rockets and 20-mm. and 40-mm. guns, were to move slowly forward toward the beach in line-abreast formation, just ahead of the first wave of amphibian tanks. As the LCI’s reached the line where the heavier fire support ships lay to, they were directed to open fire on the beach areas with their 40-mm. guns. Those off the northern beaches (Green and Red) were to stop dead in the water at this line, let the leading waves pass through them, and continue to fire as long as safety to the landing craft permitted. No rockets were to be fired by the northern group of gun boats since the reef in this area would keep them out of effective range of the beach (1,100 yards). At the southern beaches (Blue and Yellow), LCI(G)’s were ordered to proceed at a distance two hundred yards ahead of the first landing craft until they reached a line 1,000 yards off the beach, then fire their rockets and 40-mm. guns as long as safety allowed.

Just as impressive as the plans for preparatory naval fire were those for pre-landing aerial bombardment. Mitscher’s Task Force 58 had made its first strike against the islands of Guam, Rota, Tinian, and Saipan on 23 February, and thereafter on the occasions when aerial reconnaissance missions were flown across the islands some bombs were released, although with dubious results. According to the original plans, however, not until two days before the scheduled landing on Saipan would a heavy and prolonged aerial bombardment of that island and Tinian be undertaken.

The fast carriers of Mitscher’s force, working in conjunction with escort carriers under command of Admiral Turner, would undertake this task. One D minus 2 (13 June) planes from the fast carrier force were to make fighter sweeps on airfields on both Saipan and Tinian to destroy enemy aircraft. On the same day thirty-three planes would deliver counterbattery fire against guns firing on the mine sweepers. Combat air patrol and antisubmarine patrol missions were to be flown simultaneously.

The next day a more intensive program of destruction was to be undertaken. Inland coast defense and dual-purpose and antiaircraft guns were to be bombed heavily. Cane fields not already burned were to be fired. Other priority targets were inland defense installations and structures, the buildings around Aslito airfield, and communications and transportation facilities on the west coast of Saipan including small craft, radio stations, observation towers, railroad and road junctions, and vehicles. The same day six smoke planes were to provide protection for underwater demolition teams operating close offshore, if necessary. Also, vertical photographs were to be made of all beaches from Tanapag Harbor to Agingan Point.

On 15 June, in addition to continuing most of the above duties, a heavy half-hour aerial attack on both islands was to be carried out and to be terminated only one hour before the scheduled landings. During this period naval gunfire was to be lifted so that planes could fly in low for precision bombing and rocketing of enemy installations. A total of 60 fighters, 51 dive bombers, and 54 torpedo bombers were to take part in this final preliminary saturation attack. Thereafter, until the carriers were withdrawn, the carrier-based planes would act as aerial observers for land-based artillery, make photographic sorties, lay smoke on request, and provide deep and close support for the troops ashore. For the critical movement of assault troops from ship to shore the plans followed, with some variation, the pattern used so successfully in the Marshalls operation.

Astern of the LCI gunboats, amphibian tanks (LVT(A)’s) would constitute the bulk of the leading wave. They mounted either 75-mm. howitzers or 37-mm. guns plus machine guns, and their first job was to lead the waves of assault amphibian tractors (LVT’s) from the reef’s edge to the shore line. The LVT(A)’s Would provide the only close fire support for the assault troops during the critical few minutes between the time that naval gunfire and aerial bombardment were compelled to lift and the time that the infantrymen actually hit the beach’s edge.

Moreover, for the Saipan landing the mission of the amphibian tanks was not to cease at the shore line. On the 4th Marine Division beaches, the tanks of the 708th Amphibian Tank Battalion (Army) were to push inland approximately 1,500 yards to the first objective line and set up a perimeter defense closely supported by infantry in the amphibian tractors. To the northward, in the 2nd Marine Division’s zone of action, the 2nd Armored Amphibian Battalion (Marine) was ordered to move four companies of its amphibian tanks inland only about three hundred yards to the tractor control line and there cover the debarkation of assault troops from its LVT(A)’s. Thereafter, most of the amphibian tanks were to remain under cover and engage targets as far inland as 1,500 yards, but only on call from the infantry. Thus, LVT(A)’s were scheduled to proceed beyond the beaches’ edge and to act, to all intents and purposes, as land tanks until such time as heavier tanks could be brought ashore. This was an innovation in amphibious techniques and one that, as events developed, proved to be of dubious merit.

Training and Rehearsals

With the conclusion of the Marshalls operation, it became apparent that the future promised a shift in the Central Pacific Area from atoll warfare to operations on larger land areas that were both mountainous and jungle-covered. Hence, even before the official warning orders came down from corps headquarters, all three divisions assigned to Northern Troops and Landing Force had commenced training their troops to meet the particular conditions that the forthcoming campaign would impose.

The 27th Division, stationed on Oahu, made an early study of the methods of burning sugar cane and the movement of foot troops through freshly burned fields. Groups from all of the infantry regiments conducted exercises in methods of burning fields, cutting passage through them, and the movement of large and small numbers of troops through standing arid freshly burned cane.

The division also concentrated heavily on training its men in combined tank-infantry operations. All infantry companies engaged in field exercises involving the use of tanks in direct support, a particularly important exercise for the Army division since its tank battalions were not organic but were specifically attached to the infantry for the Marianas operation. Other specialized training included intense education in amphibious communications procedures. The 295th Joint Assault Signal Company (JASCO) was attached to the division sufficiently far in advance to allow for thorough familiarization of the infantry battalions with the functions and abilities of the various JASCO teams.

All units were instructed in the proper organization and plan of fires for a night perimeter defense, A period of five weeks was devoted to the study and practice of methods of loading 105-mm. howitzers in amphibian trucks (DUKW’s). Combat engineers were instructed in the use of flame throwers and demolitions for the reduction of fortified positions. The 27th Cavalry Reconnaissance Troop conducted rubber boat training with emphasis on beach reconnaissance, hydrographic studies, and night landings.

The 2nd Marine Division boasted excellent training facilities in the vicinity of its “Camp Tarawa” on the main island of Hawaii. It too held special exercises in the techniques of fighting through sugar cane. Also, the jungle and mountainous terrain on Hawaii approximated the type that the division would meet on Saipan and was ideal for the simulation of realistic combat conditions.

The 4th Marine Division fared less well. Its camp site on Maui was new, its living and training facilities were incomplete. Hence, camp construction and training had to be carried out simultaneously—a situation that, though common enough in the Pacific, was never desirable. Nevertheless, by instituting emergency measures for the acquisition of suitable land and through co-operation with the Navy and Army authorities, “a fairly satisfactory schedule of individual, unit and combined training was completed,” according to the division’s commanding officer.

The chief training problem facing XXIV Corps Artillery was that of converting two coast artillery battalions into field artillery battalions. The XXIV Corps Artillery was not activated as a unit until the end of March 1944. At that time the 225th Field Artillery Group was alerted to take part in the Marianas operation and relieved of its defensive mission on Oahu. Two of its field artillery battalions were detached, and the 32nd Coast Artillery Battalion and 2nd Battalion, 55th Coast Artillery, were attached.

As finally organized, the XXIV Corps Artillery was made up of one 155-mm. howitzer group of two battalions and one 155-mm. gun group of two battalions drawn from available field artillery personnel and supplemented by coast artillery personnel. Because of its infancy as an organization and the lack of combat experience of most of its personnel, adequate training for the unit was urgent.

Coast artillery officers were immediately given an intensive education in basic field artillery methods, and a similar program for enlisted personnel followed. Demonstrations held by field artillery batteries and battalions were followed by four field exercises per week. On 1 May two batteries of the 53rd Field Artillery Battalion were loaded on an LST and taken to Maui to experiment with methods of loading 155-mm. guns and to obtain training in unloading across sandy beaches. Experiments were also conducted in loading the 155’s on the smaller LCT’s (landing craft, tank). Because of the shortness of time and its relative lack of basic training, XXIV Corps Artillery did not participate in the final grand rehearsal. Instead, the two-month intensive training period culminated in a corps artillery field exercise held during the rehearsal period.

On 14 May ships carrying the two Marine divisions with their full loads of equipment rendezvoused in the area of Maalca Bay, Hawaii, for final rehearsals before shoving off to Saipan. LVT’s and other amphibious craft were launched; the assault battalions practiced ship-to-shore movements; shore party team personnel and beach parties were landed with their communications equipment; artillery was beached and dragged ashore. On 16 and 17 May each of the divisions made a coordinated landing on the island of Maui and battle conditions were simulated as far as was practicable. However, in view of the fact that the island was populated, ship and aerial bombardment had to be “constructive” only. Moreover, the landing beaches were separated and maneuver area ashore was extremely limited, preventing rehearsal of co-ordinated movements inland and any extensive deployment of troops once they had reached the shore line. As an exercise in ship-to-shore movement the rehearsal was useful, but it failed to give the troops an adequate foretaste of the problems involved in consolidating a beachhead once they had landed.

Finally, on 19 May, a simulated landing was made jointly by the two Marine divisions on the nearby island of Kahoolawe. This time troops approached the shore under actual cover of naval and aerial fire. On reaching a line 300 yards from the beaches they turned back, but in every other respect the exercise was a full-dress rehearsal of the plans for the forthcoming landing on Saipan, with units, positions, intervals, distances, and other details as prescribed in the operation plans. This was followed immediately by a second exercise in which air and naval gunfire did not take part. Then troops were re-embarked in the vessels in which they were scheduled to sail overseas and returned to their respective rehabilitation areas.

The only incident that had marred last minute training was the loss of three deck-loaded LCT’s over the sides of the LST’s that were carrying them to the rehearsals. This resulted in twenty-nine casualties to the 2nd Marine Division. Moreover, two of these LCT’s had been specially equipped with 4.2-inch mortars. Plans called for their employment on Saipan as support ships to supplement the rocket-firing LCI’s in the last minutes between the lifting of heavy ships’ fire and the landing of troops. Their loss during rehearsals prevented the equipment from being tested until a later operation and deprived the assault troops of that much additional naval support.

From 18 to 24 May the 27th Division (minus its artillery), fully loaded on three transport divisions, conducted similar rehearsals. The exercise emphasized the technique of debarking and landing a large number of troops with a limited number of boats, a situation thought likely to occur if reserve troops had to be landed at all on Saipan. Ship-to-Shore communication was established although, as in the case of the two Marine divisions, no supplies were unloaded since all ships had already been assault loaded for the actual landing.

Loading and Embarkation

The task of carrying three reinforced divisions and almost seven thousand corps and garrison troops with all their supplies and equipment over a distance of 3,200 miles from Hawaii to Saipan was the heaviest yet imposed upon the Navy in the Pacific war. To accomplish it, Admiral Nimitz assembled a flotilla of no naval transport vessels of all varieties—37 troop transports (APA’s and AP’s), 11 cargo ships (AKA’s and AK’s), 5 LSD’s (landing ships, dock), 47 LST’s, and 10 APD’s.

In addition, a whole division of Liberty ships had to be organized to transport the 106th Regimental Combat Team because of the scarcity of Navy troop transports in the area. Altogether, a total of 74,986. measurement tons of cargo representing 7,845,194 cubic feet was loaded. By comparison, during the invasion of Kwajalein in January 1944, only 49,283 tons were carried in the assault shipping. Nimitz’ operation plan provided that assault and garrison forces should be allowed 32 days of Class I supplies (rations), 20 days of Class II (organizational and individual equipment), 20 days of Class III (fuels and lubricants), weapons and 10 for antiaircraft weapons.

Staging areas for the three divisions were widely separated and not all were conveniently located. Ships assigned to the 2nd Marine Division loaded at Hilo on the main island of Hawaii, those of the 4th Marine Division at Kahului, Maui, and those of the 27th Division at Oahu. The ports of Kahului and Hilo were ill suited to loading the two Marine divisions efficiently. The piers at each could berth only four ships alongside the dock at one time. There were not enough dock cranes, stevedore equipment, and warehouses. There were no dock lighting facilities, and it was difficult for LST’s to beach properly. Also, Hilo was some sixty miles away from the 2nd Marine Division’s Camp Tarawa, which complicated the problem of loading both troops and equipment.

Standard combat unit loading procedures were followed as a rule, but shipping shortages sometimes made this impossible. This was especially true of supplies and equipment belonging to V Amphibious Corps troops, XXIV Corps Artillery, and garrison troops. The last available AP in the Pacific (USS G. F. Elliott), two AK’s (USS Hercules and USS Jupiter), and two LST’s were assigned to lift these units, but the shipping space was inadequate. Excess personnel (approximately 4,000) were distributed among the transports carrying the two Marine divisions. As a result most of these units, especially the XXIV Corps Artillery, were separated from their cargo. In other words these particular units were “convoy unit loaded”—which was highly undesirable from the point of view of tactical disposition.

Even after parceling out more than half of its attached troops to the ships carrying the Marine divisions, V Amphibious Corps still did not have enough room aboard its own vessels. It was impossible to combat load its cargo. To have tried to vertically load each of the twenty-five units carrying cargo on the corps ships would have meant leaving from 25 to 35 percent of the cargo behind. The upshot was that a top priority was assigned to corps artillery and the corps signal battalion, and the remainder of the units’ equipment was stowed wherever it could be fitted in.

As early as 1 May 1944, Holland Smith’s headquarters had ordered 25 to 50 percent of all supplies and two to five units of fire to be palletized. The object was to permit rapid transfer from the beach to inland dumps by using tractors to drag the pallets instead of resorting to the older method of trucking loose supplies inland employing manpower to load the trucks. From the outset, the two Marine divisions were lukewarm toward the project, and in the end loaded only a few pallets. The 27th Infantry Division, however, had had several months’ experience in handling palletized cargo and was enthusiastic about this technique for loading and unloading supplies. The division not only complied with corps orders, but went beyond it and palletized between 80 and 90 percent of all supplies.

One reason for the Marine divisions’ failure to follow suit was inexperienced labor and a shortage of equipment. The 4th Marine Division reported that it could procure only enough material to palletize 10 to 15 percent of all supplies and that the job was done so poorly that some pallets broke down during handling. In the end, the division decided that palletization of supplies at least for the initial stages of the assault was not worth the trouble. The marines argued that palletized supplies took up too much space aboard ship, were difficult to transfer from one type of landing craft to another, and required too much extra equipment. Furthermore, it was contended that pallets were not practical where dumps were located more than 500 yards inland and where reefs were encountered.

Neither corps headquarters nor the 27th Division agreed. Holland Smith’s transport quartermaster maintained that the “reasons for palletization overbalance the negative effects,” and cited as the primary benefits the rapid unloading of landing craft at the beaches and the release of large working parties formerly engaged in transferring cargo from landing craft to trucks. The 27th Division headquarters was so enthusiastic about the process that it diverted from training one and sometimes two companies of infantry in addition to a platoon of engineers for a period of six weeks just to palletize supplies.

Amphibian tanks and tractors, the all-important vehicles of assault, were as usual transported aboard LST’s. Each LST carried seventeen LVT’s, loaded in two rows of eight with the odd one secured on the ramp. By loading LVT’s in this manner, about fifteen feet of clear space remained on the after portion of the LST tank deck, and emergency supplies were “preloaded” thereon. In addition to the amphibian vehicles, each LST carried more than 300 marines from Hawaii to Eniwetok. There, they received fifty to seventy-five more from transports to fill the complement of the assault waves. A serious LST shortage almost occurred when six were destroyed by fire at Pearl Harbor on 21 May. However, LST’s originally assigned to the garrison force were used as substitutes, and loading and embarking was only delayed twenty-four hours.

One impediment to well-planned and well-coordinated combat loading was that troop transport quartermasters too often received insufficient or inaccurate information on the characteristics of the ships assigned to them. Precise data on the location, size, and shape of ships’ holds, the number and location of hatches and winches and other equipment, plus myriad other details concerning ship structure are essential to proper combat loading. This was not always forthcoming. New ships arrived at the very last moment, and there was little or no time available to obtain correct ships’ characteristics. For two AP’s (USS Storm King and USS John Land) assigned to the 4th Marine Division, no characteristics were obtainable before actual loading. The division’s supply section had been instructed to assume that these vessels’ characteristics were similar to those of another AP, USS LaSalle. Upon arrival of the ships, it was discovered there was no such resemblance, that the new ships were not entirely suitable for combat loading, and that the winchmen were inexperienced and too few in number to cope with the problems at hand. Hence, many valuable items of equipment, especially twenty-five 2½-ton cargo trucks, had to be left behind.

In spite of these and kindred difficulties, the three divisions met Admiral Turner’s loading schedule. By 14 May both the Marine divisions were aboard their transports and ready to depart for rehearsals, completely loaded except for a few last-minute items. By 18 May the 27th Division was also set to go.

After a brief period of rehabilitation following rehearsals, all units of Northern Troops and Landing Force once again boarded their ships and prepared to set sail for the final ordeal. The slower LST’s carrying assault elements of the two Marine divisions sortied from Pearl Harbor on 25 May. On 29 and 30 May two groups of naval transports followed. All ships carrying the assault troops rendezvoused at Eniwetok, where last-minute intelligence data was disseminated and additional troops assigned to the initial landing waves were transferred from transports to LST’s.

By 11 June the last of the attack transports had weighed anchor in Eniwetok lagoon and the mighty convoy, split into four separate groups, was steaming westward through hostile waters toward still more hostile shores. Well to the rear came the transport and tractor (LST) groups carrying the reserve troops, the 27th Infantry Division. These had sailed from Pearl Harbor between 25 May and 1 June and had rendezvoused at Kwajalein. There, the 106th Regimental Combat Team was informed that it would undoubtedly be detached to the Southern Attack Force for the invasion of Guam. Otherwise, the voyage for all units was uneventful.

The Prospects Ahead: Intelligence of the Enemy

While still at anchor in Eniwetok, the intelligence section of Headquarters, Expeditionary Troops (Task Force 56), received a final batch of aerial photographs of Saipan and the southern Marianas. These had been made on 28 May for Saipan and on 29 May and 7 June for Guam.

They were disseminated to the two Marine divisions before their departure from Eniwetok on 11 June, although the initial assault elements aboard the LST’s had left before the new information could reach them. Hence, the leading waves of troops would make their landings on the basis of information of the enemy situation as derived from photographic sorties flown on 18 April.

A final G-2 “Summary of the Enemy Situation” was prepared by Holland Smith’s intelligence section on 13 June and represents the last-minute estimate of enemy potentialities in the Marianas before the actual landing. This document predicted that the Japanese had on Saipan alone from 15,000 to 17,600 troops, with an additional 10,150 to 10,750 on nearby Tinian. Of the total, 9,100 to 11,000 were thought to be ground combat troops located on Saipan, The rest of the garrison, it was believed, was made up of air base personnel, maintenance and construction personnel (including Koreans), and a home guard. This represented a considerable increase over an estimate made a month earlier (9 May), which put the total number of enemy troops on Saipan at 9,000 to 10,000 and on Tinian at 7,500 to 8,500.

Saipan had three airfields in varying stages of preparedness. Aslito Naval Air Station in the south was 3,600 feet in length and believed to be fully operational; an emergency landing strip 3,280 feet in length had been sited in the area of Charan Kanoa; and at Marpi Point a large airfield (4,300 feet) was still under construction and was considered to be nonoperational. In addition, a major seaplane base at Flores Point in Tanapag Harbor was thought to be fully operational.

The latest estimate of air strength on Saipan before the carriers’ strikes was a total of 152 aircraft. However, on 11 and 12 June 140 aircraft were destroyed on Saipan, Tinian, and Guam, and since no aerial opposition was encountered at Saipan on 13 June, Japanese aerial resistance from Saipan was thought unlikely.

The newest photographs of Saipan revealed several significant increases in the number of gun installations since 18 April, when the last photographic sortie had been flown. The most notable of these were an increase of 32 percent in the number of heavy antiaircraft guns, 28 percent in medium antiaircraft guns, and 37 percent in machine guns.

According to intelligence estimates, the preferred landing beaches off Charan Kanoa were defended by a well-developed system of trenches, tank traps, pillboxes, and machine guns. It was assumed that infantry elements on the island would be assigned chiefly to the defense of this area.

The absence of extensive field fortifications and the presence of heavy-caliber weapons between Garapan and Flores Point suggested to intelligence officers that the defense of that area would be primarily the responsibility of artillery and antiaircraft elements of whatever guard forces, special landing forces, and antiaircraft units that were stationed on the island. Intelligence officers also believed that the machine guns around Aslito field, at the southern end of Charan Kanoa strip, and on the eastern end of Marpi Point would probably be manned by similar elements and by air base defense antiaircraft personnel.

Intelligence also led the officers to believe that the enemy probably had a tank detachment or at least an amphibious tank unit on Saipan. This, plus other factors, suggested that the Japanese contemplated a strong defense at the shore line combined with a mobile defense in the area behind the preferred landing beaches.

The last assumption was essentially correct, even if some of the detailed estimates as to the number of enemy troops and installations proved to be well under the mark. At any rate, nothing in the last minute intelligence surveys indicated that a basic change in the preferred landing plans was necessary. The die was cast. Under mild skies and through gently rolling seas the advance groups of troop-laden ships moved in slow procession toward the battleground.

SOURCE: Campaign in the Marianas; BY: Philip A. Crowl (United States Army Center of Military History)

World War Two: Marianas(2-4); Prewar Japanese Activities

World War Two: Operation Cartwheel (18) Emiau


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