The Central Pacific Battleground
In American military terminology, the scene of the proposed offensive was the Central Pacific Area, a subdivision of the Pacific Ocean Areas that extended from the western coast of North America to the shores of China and reached from the equator northward to the 42d parallel. Canton Island, just south of the equator, was included in the Central Pacific, but the Philippines and those parts of the Netherlands Indies that lay in the northern hemisphere were not.1 Admiral Nimitz, Allied commander-in-chief throughout the Pacific Ocean Areas (CinCPOA), retained immediate control over operations in the Central Pacific. Within this area lay Micronesia, a myriad of islands of varying size and type, the region in which the forthcoming Central Pacific battles would be fought.
THE GEOGRAPHY OF MICRONESIA2
That part of Micronesia nearest Japan is the Mariana group of 15 volcanic islands. The Marianas curve southward from the 20th to the 13th parallel north latitude, with the center of the chain lying at about 144 degrees east longitude. The islands themselves, five of which were inhabited at the outbreak of war, are by Micronesia standards vast and mountainous. Guam, the largest, boasts an area of 228 square miles and peaks rising to over 1,000 feet. The highest elevation in the entire group is 3,166 feet on smaller Agrigan. Although the temperature is warm but not unpleasant, rains occur frequently, and there is the threat of typhoons and an occasional earthquake. Saipan, near the center of the Marianas, lies 1,285 nautical miles southeast of Yokohama. (See Map I, Map Section.)
South of the Marianas are the Carolines, a belt of over 500 volcanic islands and coral atolls extending eastward from, Babelthuap in the Palaus, 134 degrees east longitude, to Kusaie at 163 degrees. The long axis of this group coincides roughly with the seventh parallel north latitude. At the approximate center of the Carolines, 590
miles southeast of Saipan, is Truk, site of a Japanese naval base. The climate in this area is healthful, but the average temperatures are slightly higher than in the Marianas. Some of the larger Caroline Islands are covered with luxuriant vegetation.
Northeast of Kusaie are the Marshalls, a group of 32 flat coral atolls and islands scattered from 5 to 15 degrees north latitude and 162 to 173 degrees east longitude. The highest elevation in the entire group is no more than 40 feet. Kwajalein, the largest atoll in the world, lies near the center of the Marshalls, 955 miles from Truk. The climate is hot and humid.
On a map, the Gilberts appear to be an extension of the Marshalls, an appendix of 16 atolls that terminates three degrees south of the equator. Tarawa, slightly north of the equator, is 540 nautical miles southeast of Kwajalein and 2,085 miles southwest of Pearl Harbor. Heat and humidity are extreme during the rainy season, the soil is poor, and portions of the group are occasionally visited by droughts.
The most striking feature of the Micronesia battlefield is its vastness. An island as big as Guam is little more than a chip of wood afloat in a pond. Although the total expanse of ocean is larger than the continental United States, the numerous islands add up to less than 2,000 square miles, a land area smaller than Delaware.
At one time, all of Micronesia except for the British Gilberts had belonged to Spain. The United States seized Guam during the Spanish-American War, and Spain later sold her remaining Central Pacific holdings to Germany. After World War I, the League of Nations made Japan the mandate power in the Marshalls, Carolines, and Marianas (except Guam). Under the terms of the mandate, a reward for participating in the war against Germany, the Japanese were to govern and develop the islands, but were forbidden to fortify them. This bar to fortification was reinforced by the Washington Naval Treaty of 1922.
In 1935, however, Japan withdrew from the League of Nations without surrendering her authority over the Pacific isles. Because of the strict security regulations enforced throughout the region, Japan succeeded in screening her activities for the six years immediately preceding the attack on Pearl Harbor. As late as 1939, a Japanese scholar assured the English-speaking peoples that his nation was not using the islands of Micronesia for military purposes.3 The strength of the defenses in this area would not be accurately determined until the Central Pacific campaign was underway.
THE ROLE OF THE MARINE CORPS
Throughout his arguments for an offensive across Micronesia, Admiral King had desired to use Marines as assault troops, for the Marine Corps had pioneered in the development of amphibious doctrine, and its officers and men were schooled in this type of operation.4 Major General Holland M.
Smith, who would command the V Amphibious Corps (VAC) for most of the Central Pacific campaign, had directed the amphibious training of Army troops that had participated in the invasion of North Africa. The same staff which would accompany him westward had helped him prepare elements of the 7th Infantry Division for the Attu operation.5 Experienced leadership would not be lacking, but veteran Marine divisions were at apremium.
Three Marine divisions, two of them proven in combat, were overseas when Admiral Nimitz received the JCS directive to prepare plans for a blow at the Gilberts. The 2d Marine Division, which was recovering from the malarial ravages of the Guadalcanal campaign, continued to train in the temperate climate of New Zealand after its release to Admiral Nimitz and incorporation into General Holland Smith's amphibious corps. The other malaria-riddled veteran unit of the battle for Guadalcanal, the 1st Marine Division, was in Australia. This division was left in General MacArthur's Southwest Pacific Area to execute a part of the revised ELKTON plan, the landing at Cape Gloucester on New Britain. The 3d Marine Division, untested in combat and new to Vice Admiral William F. Halsey's South Pacific Area, was completing its movement from New Zealand to the southern Solomons where it would train for the invasion of Bougainville, an operation that was to begin in November 1943. Although still in training in the United States, the 4th Marine Division was scheduled to be ready by the end of 1943 for service in the Central Pacific.
Also present in the South Pacific were several other Marine combat organizations larger than a battalion in size. The 1st Raider Regiment was committed to the Central Solomons offensive; one battalion was already fighting on New Georgia, and another had just landed on that island. The 1st Parachute Regiment, an airborne unit in name only, was preparing in New Caledonia for possible employment during the advance into the northern Solomons. The 22d Marines, a reinforced regiment that eventually would see action in the Central Pacific, was at this time standing guard over American Samoa.6
Like the ground combat units, the bulk of Marine Corps aviation squadrons overseas at the time were stationed in the distant reaches of the South Pacific. An exception was the 4th Marine Base Defense Aircraft Wing. Although the wing, at the time of the JCS directive, was preparing to shift its headquarters from Hawaii to Samoa and most of its squadrons were staging southward, one fighter and one scout-bomber squadron were in the Ellice group near the northern boundary of the South Pacific Area. Since the planes based in the Ellice Islands were short range craft and the pilots unused to carrier operations, neither unit could participate in the Gilberts
invasion.7 At Tarawa, the 2d Marine Division would be supported by Navy carrier squadrons.
TACTICAL ORGANIZATION OF THE MARINE DIVISION
The Marine division that figured in Admiral Nimitz' plans for the Gilberts was organized according to the E series tables of organization adopted in April 1943. With an authorized strength of 19,965 officers and men, the division was constructed in a triangular fashion--three infantry regiments, each of which had three infantry battalions. This arrangement enabled the division commanding general to hold in reserve an entire regiment without impairing the ability of his command to attack or to remain on the defensive. A regimental commander could exercise this same option with his battalions, and the battalion commander with his rifle companies, as well as with a headquarters company and a weapons company. An infantry regiment was authorized a basic strength of 3,242, a battalion 953, and a rifle company 196.
Supporting the divisional infantry components were an engineer regiment of three battalions (engineer, pioneer, and naval construction), an artillery regiment with three battalions of 75mm pack howitzers and two of 105mm howitzers, Special Troops, and Service Troops. Special Troops, its total strength 2,315, consisted of a light tank battalion which included the division scout company, a special weapons battalion equipped with antitank and anti-aircraft guns, and the division headquarters battalion which contained headquarters, signal, and military police companies. Service, motor transport, amphibian tractor, and medical battalions, with a total of 2,200 officers and men, made up Service Troops. The division chaplains, doctors, dentists, hospital corpsmen, and the Seabees of its naval construction battalion were members of the U. S. Navy.
The infantry units, too, had their own support elements. A weapons company armed with heavy machine guns, 37mm antitank guns, and self-propelled 75mm guns was under the direct control of each regimental commander. The battalion commander had his own company of heavy machine guns and 81mm mortars, and a company commander could rely on the light machine guns and 60mm mortars of his weapons platoon.
The basic structure of both division and regiment was altered when necessary. Troops normally under corps control, such as reconnaissance, medium tank, or artillery units, might be used to reinforce the division. For amphibious operations, each regiment was made a combat team by the addition of troops from the artillery and engineer regiments, the amphibian tractor, medical, motor transport, service, tank, and special weapons battalions. These attachments increased the strength of the regiment to as much as 5,393. Some of the additional troops were reassigned to the infantry battalions, so that the combat team
generally consisted of three landing teams, each with its own engineer, artillery, medical, and tank support.8
THE ENEMY'S BASIC TACTICAL ORGANIZATION
During the drive westward, Marine divisions would be opposed by Japanese Special Naval Landing Forces as well as by the enemy's infantry divisions. When employed in the attack, a Special Naval Landing Force usually consisted of two infantry companies and a heavy weapons unit, plus communications, engineer, medical, supply and transportation elements. With a strength of 1,000-1,500, this organization was comparable in size to a Marine battalion reinforced as a landing team. Artillery support for the landing force was provided by from 8 to 24 guns and howitzers ranging from 70mm to 120mm.
On the defense, however, a Special Naval Landing Force could be reinforced to a strength of 2,000, with an appropriate increase in the number of automatic weapons and the addition of antitank guns, mortars, or both. In addition, the Marines might expect to encounter, among the naval units, trained guard forces. Construction or pioneer units, both types composed in part of Korean laborers, were engaged in building airfields and defensive installations throughout Micronesia. The strength of these organizations depended on the particular project assigned them, and their zeal for combat and state of training varied according to the policies of individual island commanders.
Like the Imperial Navy, the Japanese Army habitually altered the strength and composition of its field units to meet the task at hand. The standard infantry division consisted of some 20,000 men organized into a cavalry or reconnaissance regiment, an infantry group of three regiments, and artillery, engineer, and transportation regiments. Signal, hospital, water purification, ordnance, and veterinary units were considered parts of the division headquarters. For the most part, the Japanese adhered to the triangular concept, for each of the three infantry regiments of 3,845 men contained three 1,100-man battalions. If judged necessary, the size of a division could be increased to over 29,000 officers and men.
Usually, these reinforcements were troops not assigned to any division, for the Japanese Army had created a bewildering variety of independent units. Some were larger than the ordinary infantry regiment; others as small as a tank company. By combining independent units or attaching them to divisions, the enemy was able to form task forces to capture or defend a particular place.9
These were the forces that would battle for Micronesia. With many potential anchorages in the region, Admiral Nimitz could feint with his carriers before striking with his assault
troops. Yet, the task of destroying the individual enemy would inevitably fall to the infantryman supported by aircraft, naval gunfire, and all the firepower organic to the Marine division.
Table of Contents ** Previous Chapter (I-2) * Next Chapter (II-1)
 The Pacific Ocean Areas contained three subdivisions: the North Pacific Area north of the 42d parallel, the Central Pacific Area, and south of the equator, the South Pacific Area. Australia, its adjacent islands, most of the Netherlands Indies, and the Philippines formed the Southwest Pacific Area under General MacArthur.
 Unless otherwise noted, the material in this section is derived from: Morton MS, Introduction, p. 14; R. W. Robson, The Pacific Islands Handbook, 1944, North American ed., (New York: Macmillan Co., 1945), pp. 132-175; Fairfield Osborne, ed., The Pacific World (New York: W. W. Norton and Co., 1944), pp. 155-159.
 Tadao Yanaihara, Pacific Islands under Japanese Mandate (London: Oxford University Press, 1940), p. 305.
 King and Whitehill, Fleet Admiral King, p. 481.
 Jeter A. Isely and Philip Crowl, The U. S. Marines and Amphibious War, Its Theory, and Its Practice in the Pacific (Princeton: Princeton University Press, 1951), pp. 61-63, hereafter Isely and Crowl, Marines and Amphibious War.
 StaSheet, FMF Grid, dtd 31Ju143 (HistBr, HQMC).
 StaSheet, Air, dtd 31Ju143 (HistBr, HQMC); Robert Sherrod, History of Marine Corps Aviation in World War II (Washington: Combat Forces Press, 1952), pp. 222, 224, 438-439, hereafter Sherrod, Marine Air History.
 OrgChart, MarDiv, dtd 15Apr43 (SubjFile: T/Os, HistBr, HQMC ). A copy of this table of organization and equipment is contained in Shaw and Kane, Isolation of Rabaul, pp. 571-573.
 WD, TM-E 30-480, Handbook on Japanese Military Forces, dtd 15Sep44, pp. 19-21, 76-81.