Before Pearl Harbor: Under the terms of Article 22 of the Covenant of the League of Nations, Japan was bound to prevent “the establishment of fortifications of military and naval bases” in the former German possessions in the Pacific mandated to her—the Marianas, Palaus, Caroline’s, and Marshalls.
The neutralization of other Japanese-held islands was guaranteed by the Washington Naval Limitations Treaty of 1922, signed by the United States and Japan, as well as by the British Empire, France, and Italy. On 27 March 1933, Japan gave the required two years’ notice of her intention to withdraw from the League, and the official withdrawal was consummated on 27 March two years later. This action, being unilateral, did not relieve Japan of her obligation not to fortify the mandated islands under the terms of the Covenant. However, the League was powerless to enforce the Covenant and after 1935 the islands were for the most part closed to foreign visitors. From 1935 until 1944 the nature and extent of Japanese activities in the mandated islands remained veiled in mystery.
One inevitable result of this policy of exclusion, coupled with the known aggressive intentions of the Japanese Empire on the Asiatic mainland, was in the late 1930’s to raise grave suspicions among the Western powers that Japan was fortifying the islands contrary to her commitments stipulated under the terms of the League Covenant. One Australian commentator put it, “It is believed that Japan has assembled, in these islands, equipment and supplies which would be of great value to her in any policy of aggression.” Evidence brought to light since the close of World War II amply justifies the suspicion.
From 1934 through 1941 the Japanese undertook considerable construction activity in their island possessions, allegedly for nonmilitary purposes. According to the testimony of Captain Hidemi Yoshida, IJN, who was intimately connected with naval construction in the mandates, this program was aimed primarily at the building of “cultural and industrial facilities.” Under the category of “cultural and industrial facilities” were listed such items as ramps and runways for aircraft, wireless stations, direction finders, meteorological stations, and lighthouses. These improvements, Yoshida claimed, were necessary for safe navigation, promotion of commerce, and other peaceful pursuits.
Unquestionably many of these installations could be employed for commercial purposes. It is equally true that their nature was such as to permit an easy conversion to military uses, if the situation so demanded. It also appears certain that the Japanese made a deliberate effort to disguise military construction projects in the cloak of harmless peaceful endeavors. For example, in 1940 the Naval Secretariat set aside the sum of 4,635,750 yen ($1,086,619.80) for lighthouse construction throughout the Palaus, Caroline’s, and Marshalls. Among the items authorized for these “lighthouses” were military barracks, generators, ammunition storage buildings, command posts, lookout stations, roads, and water storage facilities. No mention was made of towers, searchlights, bells, foghorns, or the other paraphernalia usually associated with such aids to navigation. Whatever the extent of Japanese military construction in the Pacific islands was before 1940, it is clear that from that year until the outbreak of war with the Allied Powers in December 1941 the mandated islands were being fortified as rapidly as conditions would permit.
Late in 1939 the 4th Fleet of the Imperial Japanese Navy was organized and charged with the mission of protecting the mandated area. With headquarters at Truk, the 4th Fleet’s area of command roughly coincided with the area mandated to Japan. After the commencement of hostilities Wake, Guam, the Gilberts, Nauru and Ocean Islands were added. This “fleet” had only a few combat vessels under its command, its primary duties being to build up and defend air and naval bases in Japan’s island possessions. Throughout 1940 the 4th Fleet existed mostly on paper, and did not really start to grow until the end of the year.
About the same time that the 4th Fleet was being activated, the Imperial Navy sent a large team to survey the Marshalls with the object of laying plans for a fairly large-scale construction program. Up until late 1939 far more attention had been devoted to the Caroline’s and Marianas than to the more distant Marshalls. Now, improvements in warships and naval weapons, and especially the advent of heavy land-based bombers, forced the Japanese to re-evaluate the importance of the Marshalls and to concentrate more heavily on their defense.
In January 1941, the 6th Base Force was activated as a subordinate command and assigned to the Marshalls, where it remained to command the Marshalls sector until destroyed by the American invasion of Kwajalein. At the same time, a subordinate unit, the 6th Defense Force, was also activated and arrived in the Marshalls in March. Finally, in September 1941, three guard forces (the 51st, 52nd and 53rd) were activated and ordered to the Marshalls where they were made directly responsible to the 6th Base Force for the defense of Jaluit, Maloelap, and Wotje. Similar units were dispatched to the other mandates at the same time.
Concurrently with this movement of troops and workers into the Marshalls, airfield construction in the area was accelerated. Early in 1941 the 4th Fleet assumed control of all unfinished aircraft installations and also commenced many new projects. Most of the money appropriated for the defense of the mandated islands was allocated to the building of airfields and their aircraft facilities. During the period 16 November 1940 to 31 May 1941, a total of 49,526,396 yen ($11,608,987.22) was appropriated for airfield and seaplane base construction and this figure represented about 70 percent of the total sum appropriated for the erection of defenses in the islands.
Work on other types of installations was also commenced and in most cases completed before the attack on Pearl Harbor. Communications installations were concentrated on the four islands or atolls where four base force headquarters were located—Truk, Saipan, Palau, and Kwajalein.
Barracks were placed on the most important islands and atolls, while office construction was concentrated mostly at Truk, with lesser concentrations at Saipan and Palau. Saipan and Palau were supply centers and staging points for the advance into the Philippines and into the south after the start of the war. Fuel oil and coal storage facilities, including tanks and pumps, were highly important since they extended the effective range of the Japanese fleet beyond the main bases in the homeland. Such facilities had been located at Saipan, Truk, Palau, Ponape, and Jaluit according to earlier appropriations. Later construction projects activated near the close of 1941 under 4th Fleet administration included fueling facilities at Wotje, Taroa, Roi, Eniwetok, and Kwajalein, all in the Marshalls. Submarine bases were established at Truk, Ponape, and Roi. Gun positions were placed on Palau, Saipan, Taroa, Roi, Wotje, and Jaluit in the latter part of 1941. As was the case in fueling facilities, the Marshalls were developed as military bases later than the Marianas and Caroline’s.
First, priority went to Truk, Saipan, and Palau, with concurrent but less important developments of Ponape, Pagan, and Tinian. Later, priority was given to four atolls in the Marshalls—Jaluit, Wotje, Maloelap, and Kwajalein—with minor attention to Majuro and Eniwetok. Water installations, command posts, ammunition storage facilities, and minor fortifications were ubiquitous.
Prewar Japanese records of garrison forces stationed in the Marshalls leave no doubt that extensive military developments were undertaken before Pearl Harbor. The 6th Base Force, which was assigned the mission of defending these islands, reached Wotje early in 1941. It was transferred the following August to Kwajalein, which then became the administrative center of the Marshalls sector of the 4th Fleet’s area of responsibility. The main troop concentrations under the 6th Base Force coincided with the concentration of construction projects on the four atolls of Kwajalein, Wotje, Jaluit, and Maloelap. Mille, which was to be extensively developed during the war, was at this time merely a lookout station. The mission of the 6th Base Force was to defend the Marshall Islands and adjacent sea areas, plan the rapid completion of accelerated military preparations within the area and strengthen preparations for actual combat, plan and supervise all types of measures relating to defense and attack and for supply and transportation service, engage in all types of combat training, and conduct weather observation in the Marshalls area.
The 6th Defense Force, which reached the Marshalls in March 1941, included four gun batteries distributed, one battery apiece, to Wotje, Kwajalein, Maloelap, and Jaluit. Its mission was to construct gun positions and other defense installations on each of these islands; supply ships, special lookout stations, and weather stations; send out antiair and antisubmarine patrols; and conduct accelerated training for all types of warfare.
Still another group assigned to the Marshalls was the 6th Communications Unit, whose prewar missions were to maintain communications and liaison in the Marshalls area, with fleet units, and with the homeland, and to intercept foreign communications. Finally, the 51st, 52nd, and 53rd Guard Forces arrived at Jaluit, Maloelap, and Wotje in October and November 1941 with the general duties of defense of those atolls.
Thus it can be seen that, in the year or more preceding the attack on Pearl Harbor, the Marshalls along with the other mandated islands were becoming rapidly integrated into the Japanese defensive system. Contrary to the Covenant of the League of Nations and to the treaty of Washington, Japan had fortified those islands, established air bases there for military purposes, and garrisoned them with armed troops. With the outbreak of actual hostilities this program was to be rapidly accelerated.
From Pearl Harbor to the Eve of Invasion of the Marshalls
The period from the beginning of the war to the middle of 1943 saw considerable expansion of the 6th Base Force. Wake, after its seizure, was placed under 6th Base Force command and extensively developed. Early in 1942 Makin was made a seaplane base and, after Carlson’s raid, the Gilberts with Nauru and Ocean were strongly garrisoned by forces under 6th Base Force command. During this eighteen-month period, Mille was transformed from a lookout station to a major base, while installations and fortifications on Kwajalein, Jaluit, Maloelap, and Wotje were constantly improved.
In June of 1943 the 66th Guard Force was activated at Yokosuka and assigned to Mille.14 Originally, the Japanese had intended to use this atoll as a staging point for aircraft in a proposed campaign against the Ellice, Fiji, and Samoan Islands, a plan abandoned after the American invasion of the Gilberts. Some air facilities were completed by November 1942, but the atoll was not fully developed until a year later. By that time Mille was one of the best defended atolls and had the largest garrison in the Marshalls if Kwajalein and Roi-Namur are counted separately. The latter half of 1943 was distinguished by a marked increase in the number of troops, especially Army personnel, dispatched to the Marshalls. Up to that time the Marshalls had been garrisoned exclusively by Navy units, but in early 1943 it had become apparent to the Japanese that they were faced with a series of probable defeats so long as their forces continued to be tied up in the Solomon’s-New Guinea area. The deterioration of the Japanese position in the southeast posed a threat to the island garrisons of the Central Pacific, which were considered too weak to ward off American attack. The Japanese responded by drawing Army units from the Philippines, Manchuria, and the homeland and dispatching them to the Central Pacific.
By the end of August 1943 the Japanese position in the Southeastern Pacific Area was such that all thought of offensive operations had to be abandoned. The surrender of Italy on 8 September was a further blow to the Japanese Empire, for it was felt that a powerful portion of the British fleet would be freed to bring pressure on the Indian Ocean front. Until this time, the Japanese defense perimeter had run through the Marshalls, Gilberts, the Southeastern Pacific Area, the Netherlands Indies, and Burma. Now the Solomon’s and New Guinea were cracking, exposing the Gilberts and Marshalls to the ever-increasing danger of American attack.
Hence, the old defensive perimeter had to be abandoned and a new one erected in its place. On 15 September Imperial General Headquarters decided to contract the perimeter to a line running from the Banda Sea through the Caroline’s and Marianas. The new line was to be made impregnable to American assault during the time gained by delaying actions in the Marshalls and Gilberts, and in the Japanese Southeastern Pacific Area. Thus, these areas were written off as a loss as early as September, but the Japanese were determined to make the American advance toward their new perimeter as costly as possible in order to gain time and wear down the American will to fight. It was in accordance with this strategic concept of fighting a delaying action in the Marshalls that Imperial General Headquarters decided to send large numbers of Army reinforcements there in September 1943.
Army units in Japan, the Philippines, and Manchuria were reorganized as amphibious brigades and South Seas detachments, and dispatched to the Central Pacific as fast as possible.18 Even though the Marshalls had been written off as indefensible from the long-range point of view, they received a considerable share of the Army reinforcements because of the Japanese intention to conduct strong delaying actions there. The troops were distributed mostly on the periphery—on the atolls and islands of Wake, Eniwetok, Kusaie, and Mille. Kwajalein, Jaluit, Maloelap, and Wotje already had sizable garrisons, while those on the peripheral islands, except Wake, had been previously quite small.
By January of 1944 Army troops in the Marshalls, Wake, and Kusaie totaled 13,721. The units involved were the 1st South Seas Detachment; the 1st Amphibious Brigade, A Detachment; the 2nd South Seas Detachment; and the 3rd South Seas Garrison Detachment. They were distributed among the islands and atolls as follows: Kwajalein, 933; Jaluit, 620; Maloelap, 404; Wotje, 667; Mille, 2,530; Eniwetok, 2,586; Wake, 2,050; and Kusaie, 3,931.
As of January 1944 their air installations in the area included, in the Kwajalein Atoll, an uncompleted land base on Kwajalein Island, a land base on Roi, and a seaplane base on Burton; elsewhere in the Marshalls, land bases on Maloelap, Wotje, Mille, and Eniwetok, and seaplane bases on Jaluit, Wotje, Majuro, Taongi, and Utirik.
During the month of November 1943 the Japanese lost about 71 planes in the Marshalls, chiefly as a result of carrier and land-based strikes incident to the American invasion of the Gilberts. Nevertheless, they were able to balance almost all of these losses with reinforcements flown from the homeland and from the 3rd Fleet at Truk. The planes from Truk, 32 in number, represented virtually all the remaining carrier air, and most of these fell victim to American attack by the end of November. By 25 January 1944, Roi had about 35 planes; Kwajalein Island, about 10 reconnaissance planes; Maloelap, 50 planes; Wotje, 9; and Eniwetok,. As American aerial attacks on the Marshalls were stepped up in December and January, Japanese air strength dwindled rapidly.
Mille, Jaluit, and Wotje ceased to be effective as air bases. Wotje had from 30 to 35 planes in November, but this force was almost completely destroyed by two American carrier strikes. By 29 January there were only twelve “Kates” on Wotje; that day six failed to return from a mission and the rest were evacuated to Roi. The Japanese managed to keep the air strength at Maloelap at 50 planes throughout November and into December, but by January only 13 fighters were operational; 40 had been damaged and grounded. On 29 January, the American carrier raid reported the destruction of 10 planes in the air, and all that were on the ground. By 1 February, the only remaining Japanese planes in the Marshalls proper were the few on Eniwetok. Thus, by the time of the American invasion, the enemy’s power to resist by aerial attack had wasted away to almost nothing. Complete mastery of the air, so essential to success in amphibious operations, had been assured to the attackers.
The Defenses of Kwajalein Atoll,: January 1944
Kwajalein Atoll had been the hub of Japanese military activity in the Marshalls since August 1941. As headquarters of the 6th Base Force, it was the nerve center of the surrounding bases. Reinforcements coming into the Marshalls almost invariably passed through Kwajalein, to be parceled out from there. Supplies were usually distributed from this atoll, which was the closest major base to Truk and to the supply lines from the homeland. Branches of various departments of the 4th Fleet were located there to supervise supply, transportation, and the more technical aspects of construction. Kwajalein was the center of communications not only for all other bases in the Marshalls, but for the Gilberts, Nauru, and Ocean as well. The air base on Roi commanded all Japanese air forces in the Marshalls and Gilberts. All this gave Kwajalein some of the characteristics of a rear area, with more red tape than bullets, far from the front-line outposts on the periphery of the Marshalls. As a matter of fact, an American amphibious landing on Kwajalein was discounted by most Japanese as only a remote possibility, and it was fortified accordingly. As one Japanese naval commander put it, speaking of the Japanese estimate of American intentions after the Gilberts campaign: “There was divided opinion as to whether you would land at Jaluit or Mille. Some thought you would land on Wotje but there were few who thought you would go right to the heart of the Marshalls and take Kwajalein.”
Japanese island defense doctrine in the campaigns in the Gilberts and Marshalls stressed defense at the beaches. Every attempt was to be made to annihilate the enemy before he could get ashore, and if he did reach the beaches, the defenders were to counterattack before he could consolidate his positions. Since it was assumed that the enemy might be destroyed at the beaches, the island defenses were strung in a thin line along the shores, with little or no defense in depth. This doctrine was the product of the offensive character of Japanese military thought in general, and also was influenced by the geography of coral atolls, which were composed chiefly of thin flat islands surrounding a lagoon.
Most of the islands had very little depth to defend, and the occasional wider islands or wider sections of islands were usually occupied by airstrips. Later, on Iwo Jima, which was larger than most coral islands, the American attack encountered prepared defenses in depth. Later still, on Okinawa, the Japanese abandoned completely the concept of shore defense and retired to prepare defenses some distance away from the landing beaches. This change in Japanese island defense doctrine came about as a result both of experience and of the recognition of geographic realities. But at the time of the Marshalls invasion, Japanese tactical doctrine still stressed beach-line defense to the neglect of defense in depth.
Originally the plan for defending the atoll had been based on the assumption that the attack would come from the sea. After the experience at Tarawa, the Japanese appear to have changed their minds about American intentions and shifted their emphasis from defending the ocean shores to defending the lagoon beaches of the islands. Gun positions were set up along the lagoon, trenches dug, and antitank obstructions erected to prevent or delay a landing over these beaches.
[NOTE 13-31: War Department Mission, Marshall Islands, Japanese Defenses and Battle Damage, 14 Mar 44, p. 10; Japanese Studies in World War II, No. 73, Marshall Islands Operations, pp. 34-36, OCMH./\ The following detailed description of enemy defenses on Kwajalein Atoll is derived, unless otherwise indicated, from JICPOA Bull 48-44, Japanese Defenses, Kwajalein Atoll, 10 Apr 44.]
The three most heavily defended islands of the atoll were Roi-Namur, Kwajalein, and Ebeye (Burton), in that order of strength. Roi-Namur was somewhat better fortified than Kwajalein Island, but neither approached Tarawa as to the size and number of weapons or the construction and concentration of positions. These northern islands contained four 12.7-cm, twin-mount dual-purpose guns that were divided into two batteries of two, one located near the northwest corner of Roi and the other on the northernmost tip of Namur. Four 37-mm. gun positions were established. One was located on the west shore of Roi near the southwest tip of the island, another near the northeastern corner of Roi; the other two were on the southeastern tip and in the center of the east coast of Namur.
Nineteen 13.2-mm. single-mount dual-purpose guns were located in strong points mostly along the ocean shores, from the east coast of Namur to the west coast of Roi. Ten 20-mm. antiaircraft guns were emplaced, most of them along the shore line and near the airfield taxi circles on Roi; three were part of the strong point on the northwest tip of Namur and one was located on the south shore of that island. Machine guns were emplaced in concrete pillboxes, although many of the light machine guns were not permanently emplaced, but shifted from position to position as the battle demanded. The many rifle pits and fire trenches were located in the beach areas of both islands. There were three concrete blockhouses on Roi. One was located on the southwest tip, one in the northwest corner, and one in the northeast corner. Another was in the center of the east shore of Namur. The blockhouses were all located in strong point areas, housed 13-mm. machine guns, and were probably used as command posts.
The reefs off Roi-Namur were not mined, and very few antipersonnel mines were encountered inland. Wire entanglements were found at two points—on the beach around the northeast taxi circle on Roi, and on the narrow bit of land connecting Roi with Namur. The beach around the northeast taxi circle also boasted a tank obstacle in the form of large rocks jutting out of a rock wall. Antitank ditches had been dug throughout the two islands.
The defenses of Roi-Namur were quite clearly organized around a series of seven strong points, four on Roi and three on Namur, all on the ocean side. Starting from the southwest tip of Roi, the first was located along the southern shore of the west coast. The second and third were to the south and north of the northwest taxi circle. The fourth was on both sides of the wire and stone barriers next to the northeast taxi circle. The fifth, sixth, and seventh were on the northwest, north, and east tips of Namur, respectively. From the lagoon side the approaches were covered mostly by nothing heavier than 7.7-mm. machine guns.
Kwajalein Island was less well fortified. A study of enemy defenses, made there by the engineering officer of V Amphibious Corps after the operation was concluded, stated, “The prepared defenses of this island were surprisingly weak. . . .”
On Kwajalein, four 12.7-cm, dual-purpose twin-mount guns were divided into batteries of two, one located at each end of the island. Each battery was protected by 7.7-mm. and 13-mm. machine guns along the nearby beaches. Near each gun were two 150-cm. searchlights. In addition, the northern end of the island was guarded by a twin-mount dual-purpose 13-mm. machine gun on the lagoon shore. Several 7.7-mm. machine guns were in position on the western end and other heavy machine guns were scattered about the center of the island, some mounted on wooden sleds for easy movement to critical points.
On the ocean shore were six 8-cm. dual-purpose guns, divided into two batteries of three guns each. One battery was east of the tank ditch and the other was opposite the center of the airfield. The first had a 360-degree traverse and could fire either to seaward or landward. The other formed the nucleus of a strong point composed of a semicircle of rifle pits facing the beach supported by one heavy and one 13-mm. machine gun, and also included an observation tower, a range finder, and a 110-cm. searchlight.
Two other 8-cm. guns were in position on the lagoon shore, and the blockhouse on the main pier (Nob Pier), which jutted out into the lagoon near the northern tip of the island, had a 13-mm. dual-purpose gun on its roof and firing ports on the ground floor allowing machine guns to fire in all directions.
Other sheltered positions included about forty reinforced concrete pillboxes on the beaches of the ocean shore and at the northern and western ends of the island, and about twelve U-shaped standing pits. Fire trenches encircled the island, just inland from the beach. At intervals along the ocean shore were squad positions with ten to fifteen rifle pits each. These were usually arranged in a semicircle facing the beach and were camouflaged with grass. There was a concrete sea wall along most of the ocean shore and around the northern and western ends of the island. The section at the northern end had posts set into it, probably to act as a tank barricade. East of the area cleared for the airfield was a tank ditch extending halfway across the island, and three smaller tank ditches ran between the ocean shore and the road in the vicinity of the airfield. The lagoon shore was protected by a two-strand barbed-wire fence at the water’s edge. The large tank ditch was supported by trenches, rifle pits, and machine guns.
The fortifications on Burton were much lighter than those on Kwajalein, mostly machine gun positions and rifle pits. These were organized at the beaches with a concentration of dual-purpose machine guns grouped around the seaplane base in the lagoon. At the base of the south seaplane ramp was a 20-mm. antiaircraft machine gun. Near it, and between the two seaplane ramps, were two 13-mm. single-mount machine guns, three 7.7-mm. machine guns, and a concrete pillbox. Two 8-cm. dual-purpose guns were located on the ocean shore. The large number of empty machine gun emplacements would seem to indicate that the defenses of the island had not been completed at the time of the invasion. The few pillboxes found in the vicinity of the seaplane base were small, reinforced concrete shelters, each with two firing ports facing seaward. Most of the fire trenches and rifle pits were on the ocean side at the center of the island and at the north and south ends of the island. The total number of Japanese on Kwajalein, Burton, and other islands in the southern part of the atoll on D Day came to about 5,000 men.
The Army troops on Kwajalein consisted of the Kwajalein and part of the Wotje detachment of the 1st Amphibious Brigade. The Kwajalein detachment, under a Captain Kenzo Tsuyuki, numbered 204 men and consisted of one rifle company and one mortar platoon. The 729 men of the Wotje detachment had arrived on Kwajalein about 10 January 1944 and were awaiting transportation to their assigned location when the invasion began. They were commanded by a Colonel Tarokichi Aso and comprised the 2nd Battalion (less the 1st and 3rd Companies), three signal squads, and an engineer platoon.
The 6th Base Force headquarters in January of 1944 included about 80 military personnel and somewhere in the neighborhood of 200 civilians.36 This unit, the headquarters for all shore and surface forces in the Marshalls, was commanded by Rear Admiral Monzo Akiyama, IJN, who was the highest-ranking officer in the Kwajalein garrison at the time of the American assault. Under the 6th Base Force was the 61st Guard Force, which since before Pearl Harbor had borne the chief responsibility for defending the atoll. The main body of this force was stationed in Kwajalein Island and a detached force was on Roi. The main body was divided into two small battalions, four antiaircraft batteries, and six lookout stations, of which three were on Kwajalein and one each on Bigej (Bennett), Gea (Carter), and Ennylabegan (Carlos). Also attached to the 6th Base Force was one company of about 250 men from the Yokosuka 4th Special Naval Landing Force, which arrived in Kwajalein in October 1942.
The labor troops on Kwajalein and adjacent islands were engaged in the construction of the airfield on Kwajalein and other projects. Fourteen hundred of these were provided by the 4th Fleet Construction Department Detachment and were either Koreans or Japanese unfit for ordinary military duties. Their combat effectiveness was probably close to nil. Another 260 laborers, from Okinawa, were provided by the Sankyu Transportation Company, which was a purely civilian organization. These were used as stevedores and are not considered combat effectives.
The three remaining military units in the area were the 952nd Air Unit, the 6th Communications Unit, and the 6th Submarine Base Force. The air unit, consisting of about 160 men, was stationed on Burton, and when the invasion began the duty of defending the island fell to that unit. Since there were only enough rifles for about half the men and not even one hand grenade apiece, their combat effectiveness cannot be regarded as very important. The 6th Communications Unit handled communications command, code and voice signal, code signal dispatch and reception, and the radio direction finder equipment on Kwajalein and Enubuj (Carlson). No information is available as to the combat potential of this group of 350 men, but it was probably slight. The 6th Submarine Base Force, consisting of about a hundred electricians, mechanics, seamen, doctors, corpsmen, and maintenance men, had some weapons including thirteen machine guns and sixty rifles, but the force was established chiefly for the purpose of providing a rest and recreational depot for submarine crews and is not to be regarded as a combat unit. Altogether, of the enemy personnel in southern Kwajalein, only about 1,820 could be considered combat effectives at the time of the invasion. The remainder can be classified as only partially effective or not effective at all.
The 61st Guard Force Dispatched Force had been on Roi since before Pearl Harbor and constituted the main body of combat troops. It was responsible for operating most of the weapons on Roi-Namur above the small arms category. It was probably under the tactical if not the administrative control of Headquarters 24th Air Force, and itself exercised tactical command over all or part of the 4th Fleet laborers.
The 24th Air Force headquarters commanded all air units in the Marshalls except the 952nd at Burton, which was controlled by the 6th Base Force. This headquarters was commanded by Rear Admiral Michiyuki Yamada, who was responsible to 4th Fleet headquarters at Truk and who was the highest-ranking officer at Roi. On 25 January there were two medium bomber units, one with twelve land-based planes and one with three, and a fighter unit of twenty planes under this headquarters command.
As to the combat effectiveness of these people, it is difficult to hazard anything more than a guess since the extent of military preparedness of the air force personnel is not known. The best estimate would be that on Roi-Namur there were 345 combat effectives of the 61st Guard Force Dispatched Force; 2,150 air force personnel partially effective as combat troops; 357 4th Fleet laborers, ineffective; and about 700 miscellaneous personnel including marooned sailors whose combat effectiveness was probably nonexistent.
It would appear, then, that neither Roi-Namur nor Kwajalein Island was a formidable island fortress in the category of Tarawa or, later, of Iwo Jima. The Japanese had skimped on fortifications of this central atoll in favor of the atolls in the eastern sector of the Marshalls, which they considered more likely to be the objects of attack. By D Day Japanese air power throughout the entire Marshalls area had been reduced to ineffectiveness. Manpower in the islands under attack was of limited military value. On Roi-Namur the bulk of the enemy consisted of air force personnel; on Kwajalein a large percentage was labor troops. Even before American naval guns and aircraft and artillery placed on nearby islands had completed their bombardment of the main defenses, the capacity of the Japanese to ward off the attack was comparatively slight.
The invasion of Kwajalein Atoll was notable for the innovations in amphibious techniques and amphibious equipment used there. To these can be given much of the credit for the ease with which the operation was completed, in contrast to the earlier landings at Tarawa. But equally or more notable was the fact that the strategic planners for the operation, especially Admiral Nimitz, correctly estimated that this was a weak spot in the Japanese defense of the Central Pacific and exploited it accordingly.
The decision to bypass the eastern Marshalls and strike directly at Kwajalein was fully justified by the comparatively weak state of enemy defenses there. Hitting the enemy where he was not was impossible in the Central Pacific, since all the islands and atolls of any strategic importance were fortified. The only alternative was to hit him where he was least able to defend himself, and this was done in the invasion of Kwajalein Atoll.
SOURCE: Seizure of the Gilberts and Marshalls: BY; Philip A. Crowl, & Edmund G. Love (United States Army Center of Military History)