The Reinforcement of Oahu

The Hawaiian island of Oahu held a position of the first importance in the military structure of the United States before and during World War II. During the prewar years Oahu and the Panama Canal Zone were the two great outposts of continental defense, and, after Japan plunged the United States into a Pacific war, Oahu became an essential springboard for the offensive that was finally to crush the Japanese Empire.

What gave Oahu its military importance was the great naval base of Pearl Harbor. The Army had primary responsibility for protecting Pearl Harbor and, to fulfill this responsibility, before the war it maintained on Oahu its largest and, in many respects, its best equipped overseas garrison. The Army's objective was to make Oahu impregnable, and in April 1941 the War Department confidently described the island as the strongest fortress in the world.1  Seven months later this confidence was rudely shaken by Japan's amazingly successful attack on a major portion of the Pacific Fleet berthed and moored in Pearl Harbor, and on the Army's surrounding air installations and aircraft on the ground. The background of this Japanese venture has been one of the most intensively studied and related episodes in modern history, and this volume can add only some detail about what the Army did before and during the attack.2

The Hawaiian Department Before 1941

The Army had established its first post on Oahu more than forty years


earlier, immediately after the United States annexed the Hawaiian Islands in August 1898. Increasing Japanese-American friction in the following decade led to a decision by the Army and Navy in 1908 to make Pearl Harbor the principal American naval bastion in the Pacific.3  To protect Pearl Harbor, the Army greatly expanded its Oahu garrison and in 1913 established the Hawaiian Department as an independent command under direct War Department control. In the two decades after World War I the Army kept about it percent of its manpower on Oahu, built up formidable coastal defenses on its south shore to protect Pearl and Honolulu harbors, and installed air defenses to guard vital installations against this new element of warfare that developed so rapidly between world wars.

The Army's mission in Hawaii was defined in 1920 as the defense of the Pearl Harbor naval base against "damage from naval or aerial bombardment or by enemy sympathizers" and against "attack by enemy expeditionary force or forces, supported or unsupported by an enemy fleet or fleets." 4  The mission remained essentially unchanged until 1941, and until that year the Army did almost nothing to guard the other major islands of the Hawaiian chain against attack. In February 1941, General Marshall broadened the stated mission informally by emphasizing the responsibility of the Army for protecting the fleet as well as the Pearl Harbor naval installations.5  In practice, as events were to prove, the impact of this new instruction was blunted by the common assumption in Washington and Hawaii that no serious attack on Oahu was at all likely if the bulk of the fleet was present in Hawaiian waters.

The eight major islands of the Hawaiian chain are situated about 2,400 statute miles southwest of the California coast, and about 3,900 miles from the principal Japanese island of Honshu. The main island group extends nearly 400 miles from Hawaii-the large island which has nearly two-thirds of the total land area-northwestward to Kauai and Niihau. (Map II) Hawaii, Maui, Oahu, and Kauai are the principal islands, and the latter three are roughly of the same size. All are mountainous islands of volcanic origin, possessed of a subtropical climate that is pleasant and healthful. Oahu, the third largest island with an area of 604 square miles, owes its preeminence to two harbors along its southern shore: that of Honolulu, and the shallow lagoon seven miles to the west that after intensive development became the Navy's largest overseas base. Oahu, with less than one-tenth of the archipe-





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lago's area, had 60 percent of its population in 1940, and nearly 70 percent by the end of the Pacific war. The population of all the islands is something of a racial kaleidoscope. The largest single element in 1940 was of Japanese descent-roughly, 37 percent of the total of 423,000. On both Hawaii and Kauai those of Japanese descent outnumbered those of Caucasian descent by three to one, and on Oahu the two groups were about equal in number. Although more than three-fourths of the people of Japanese descent were American-born citizens, their preponderance in the total population had a profound influence on military thinking about what might happen in a war with Japan. Most Army and Navy officers assumed that in the absence of close military control there would be widespread attempts at sabotage, and therefore they planned for a wartime establishment under martial law. The existing Hawaiian government was that of a fully incorporated territory, with an elected legislature and a nonvoting delegate to Congress, and executive and judicial officers appointed by the President. It had jurisdiction over the main archipelago, the chain of minuscule reefs extending a thousand miles from Kauai to Midway, and two distant coral islands to the southwest.

Oahu is a diamond-shaped island having two parallel mountain ranges, which have precipitous slopes to the seaward and a broad plateau in between that spreads out as a coastal plain in the south. Before World War II Oahu's Army and Navy installations were mostly on this plateau and plain. There they were so closely intermingled and integrated with the civilian population and general economic activity of the island that military secrecy on any large scale was impossible. The Army had its headquarters at Fort Shafter in the western outskirts of Honolulu, but the main body of its troops was stationed at Schofield Barracks in the center of the plateau about ten miles inland from Pearl Harbor. The principal Army unit was the Hawaiian Division, activated in 1921; and its station at Schofield covered the Pearl Harbor base against an enemy landing on the northwest coast. It was only along this coast that the Army believed a hostile landing in force even remotely feasible. The principal Army air installations were Hickam Field, the base for bombardment aviation, adjacent to Pearl Harbor on the Honolulu side, and Wheeler Field, the pursuit and fighter base located in the interior next to Schofield Barracks.

On the day war began in Europe in September 1939, the Army commander in Hawaii, Maj. Gen. Charles D. Herron, after "taking stock" of his local outlook, informally commented to General Marshall that he would not "want to be given the job of cracking the nut" which Oahu presented to any would-be invader, because of its "encircling reefs and two coasts pro-


tected by very difficult small mountain ranges and the south shore very heavily armed [and therefore with the] prospect of fighting an entrenched division all the way across after a landing on the north shore." He admitted that Oahu was difficult to defend against "air attacks coming in from the sea." But he expressed the belief that airplane carriers could "not live in these waters as long as we have left any bombers at all;" and anyway he felt "that naval air forces, like the cavalry of old, always has in its mind, the get-away." 6  General Herron's optimism about Oahu's relative invulnerability to invasion appears to have been well founded, but two years later the Japanese certainly belied his observation about carriers.

The possibility of war with Japan had led the Army and Navy in 1924 to draft a new joint ORANGE plan to govern the conduct of such a war. Since the Limitations of Armament Treaty of 1921 barred the building of any new military defenses to the westward of Hawaii, the Pearl Harbor base and its Army defenses assumed an ever-increasing importance in Pacific war plans during the twenties and thirties. By 1938 the Navy had expended about $75,000,000 on this base, and the Army more than twice that amount on military installations to protect it. Navy plans for a Japanese war visualized the launching of a transpacific offensive from Oahu through Japanese-held islands toward the Philippines; but by 1935 the Army was convinced that such an offensive was impracticable, at least at the beginning of a war with Japan, and therefore that American strategy in the Pacific should be essentially defensive and should concentrate on holding the Alaska-Hawaii-Panama line. The last ORANGE plan revision of 1938 represented an unsatisfactory compromise of the Army and Navy positions. In any event, because of the increasing threat of war with Japan, the Army from 1935 until the autumn of 1939 accorded the Hawaiian Department top priority in the supply of equipment, and it increased the strength of the garrison by more than 50 percent, from 14,821 to 21,289 between the summers of 1935 and 1938.7

In September 1935 General Herron's predecessor in Hawaii, Maj. Gen. Hugh A. Drum, had expressed himself as far from satisfied with either the peacetime or planned wartime allotments of men and material to his department, and he also wanted to broaden the Army's mission. General Drum proposed that the mission include defense of all the main Hawaiian islands and participation in the air defense of the eastern Pacific area. He asked for


twenty-six of the new "flying fortress" heavy bombers then under development, and he proposed to construct operating fields for them on Hawaii and Kauai islands. This measure in turn would require some deployment of Army ground forces to the outer islands to protect the new airfields. The War Department rejected these proposals on the ground that the defense of ocean areas was the Navy's business and that the dissipation of Hawaii's forces would weaken the defense of Pearl Harbor, which must remain the overriding mission of the Army in Hawaii. Army plans of 1935 called for a war garrison on Oahu of more than 100,000 officers and men, and the Army planners in Washington rejected General Drum's proposal that 23,000 of these troops be put on the outer islands in wartime.8  The Joint Board confirmed these actions and held that the mission of United States forces in Hawaii was only "to hold Oahu as a main outlying naval base" and the Army's specific mission was "to hold Oahu against attacks by sea, land, and air forces, and against hostile sympathizers." 9

After a lengthy maritime strike in the winter of 1936-37 General Drum resubmitted his recommendations with the argument that the Army must extend its protection to the outer islands if it wished to assure an adequate supply of food for Oahu in time of war. Oahu produced only 15 percent of its own requirements in food, but the other islands could readily make up the deficiency in an emergency if communication was maintained with them. Again the War Department objected. In both 1935 and 1937, its basic argument against broadening the Army mission in Hawaii was the following: "If the Fleet is in the Pacific and free to act, Oahu will be, with the completion of the existing defense project, secure against any attacks that may be launched against it. It is only in the case that the Fleet is not present or free to act that the security of the Hawaiian Islands can be seriously threatened." 10  That the presence of the fleet in or near Hawaiian waters provided a more or less automatic guarantee against any serious attack on Oahu continued to be a widely held conviction both in Washington and Hawaii until the Japanese demonstration to the contrary in December 1941.

A fresh survey of Oahu's defenses, conducted in late 1937 by Col. Edward M. Markham on oral instruction of the President and Secretary of War, produced conclusions similar to those of General Drum.11  Colonel


Markham stressed the need for making the Pearl Harbor base as nearly impregnable as possible. He pointed out that despite their recent strengthening, the Army's installations for defending it were considerably less than impregnable, principally because of "the astounding advance in aircraft design and range over the past twenty years." He emphasized as "a corollary of the first order" the importance of preventing an enemy from seizing and using Oahu and its Pearl Harbor base "as a springboard of attack against our west coast territory and shipping, and the Panama Canal." Colonel Markham agreed with General Drum that substantial peacetime Regular Army garrisons should be installed on Hawaii and Kauai to operate and support new air bases and to assure Oahu of food in an emergency. Finally, he included among the basic assumptions of his report one of the more prophetic forecasts of the prewar years:

War with Japan will be precipitated without notice. One of the most obvious and vital lessons of history is that Japan will pick her own time for conflict. The very form of its government lends itself to such action in that its military and naval forces can, under the pretext of an emergency, initiate and prosecute military and naval operations independently of civil control .... If and when hostilities develop between the United States and Japan, there can be little doubt that the Hawaiian Islands will be the initial scene of action, and that Japan will apply her available man-power and resources in powerful and determined attacks against these islands.12

The slight impact of the Drum and Markham recommendations can be credited in good measure to the rising threat of Hitler's Germany and the increasing prospect of war in Europe, which from 1938 onward absorbed the major attention of the Roosevelt administration and of the War Department in particular. Although the United States Government considered that the Hawaiian Islands lay within the Western Hemisphere, new plans for hemisphere defense developed after 1938 emphasized the strengthening of the American military position in Atlantic and Latin American areas. The War Department's stand also reflected the fact that Oahu, in comparison with other overseas bases or with the continental United States itself, was already well provided with defenses, and especially with the means for resisting invasion. It had a full infantry division, a heavy concentration of coast defense guns, and from 1938 onward the more or less constant protection of the United States Fleet. But, until 1941, it had no modern Army combat planes.

One factor that altered the military security of Oahu in the years immediately preceding the Pearl Harbor attack was the increasing capabilities of


carrier-based air power. With the nearest Japanese airfield 2,100 miles away, military authorities correctly calculated that Oahu was beyond the range of land-based air power; but it could be reached by carriers, of which Japan had six in operation by August 1939, and two more under construction. In January 1938 Colonel Markham had pointed out how easy it would be for carrier-based planes to approach Pearl Harbor from the northeast. Screened by the heavy cloud cap almost continuously present over the main Koolau Range, they could cross Oahu and deliver a surprise attack on the naval base and its surrounding installations almost without warning. Since local ground defenses and unwarned pursuit planes could not hope to cope with such an attack, Colonel Markham assumed that the Army in order to fulfill its mission would have to conduct long-range aerial reconnaissance, and he recommended an Army air strength of 350 planes, to match an estimated 379 planes that Japan might possibly bring to bear in an initial all-out attack.13

The first War Department plans of 1939 for expanding the Air Corps proposed to increase the authorized number of Army combat planes in Hawaii from 124 to 256, and to include in the new allotment 140 bombers and 100 pursuit ships. In its report of June 1939 the Army Air Board explained the large number of bombers by pointing out the need for Army reconnaissance as well as striking forces to operate within a 1,000-mile radius of Oahu. Since the Air Board report like all similar prewar studies recognized that a carrier attack once launched would inevitably inflict some damage, it pointed out that the only sure means of preventing successful carrier attacks was to locate the carriers outside a 600- to 700-mile radius (the range of their attack planes plus one night's sailing) and bomb them before they could launch their planes. With strength enough to do this, Army aircraft in Hawaii could also interdict any attempt by the enemy to establish airfields on any of the other major islands.14

Under the production circumstances of 1939 any plans for strengthening Army air power in Hawaii were bound to take a long time to carry into effect, but the initial plans were further limited at the end of 1939 by general assumptions of the War Plans Division in Washington that Japan would not risk more than two of its carriers in a surprise attack and that long-range aerial reconnaissance was properly a Navy and not an Army mission. In the light of these assumptions the Army planners recalculated Hawaiian needs


for Army aircraft and allotted the Department 122 pursuit planes and 68 medium bombers. The bombers were to be used for reconnaissance only if the Navy was absent or if it asked for reinforcement.15  These two assumptions, that the Japanese would never employ more than two carriers in a surprise attack in the eastern Pacific and that Army bombers should not be used for long-range offshore reconnaissance, remained constants in Washington and Hawaiian defense thinking and planning for the next two years, and contributed substantially to Japanese success in December 1941.16

Under the revised 54-group air program of June 1940, Hawaii was allotted some additional pursuit and light bomber strength for close-in defense purposes and was scheduled to receive 68 heavy bombers- B-17's -instead of mediums. But the premises behind the new allotments were still a maximum 2-carrier threat and performance by the Navy of all long-range reconnaissance.17  During the same month General Marshall suggested sending 5 or 10 B-17's to Oahu immediately, but his G-3 (an Air officer) objected on the ground that so few would have no restraining influence on the Japanese and would inevitably be destroyed by hostile pursuit before they could help in fighting off an attack-comments which throw light on the utility of the 12 heavy bombers (only 6 of which were in commission) on Oahu on the morning of 7 December 1941.18  What the Hawaiian Air Force actually had at the beginning of 1941 was a heterogeneous collection of 115 combat planes, all of them obsolete or obsolescent. They were useful almost exclusively for training and not for fighting.19

A second factor affecting the Hawaiian defense picture was the decision to base the United States Fleet at Pearl Harbor. With Anglo-French naval power seemingly in control of the Atlantic, the United States continued after August 1939 to keep the bulk of its naval strength in the eastern Pacific. Until 1940 the principal bases for the United States Fleet were on the continental west coast, with Pearl Harbor serving as an advance base and concentration point during maneuvers. But after annual maneuvers in April 1940 the fleet, under command of Admiral James O. Richardson, was


ordered on 7 May to stay at Pearl Harbor, as a warning and deterrent to Japan. Almost immediately thereafter Hitler's smashing land victory in western Europe threatened to cripple or destroy Anglo-French naval power in the Atlantic. To retrieve the situation it appeared by mid-June to Army and Navy leaders in Washington that the United States would have to transfer the bulk of its naval strength to Atlantic waters.20

It was this prospect that led General Marshall on 17 June to alert the Panama and Hawaiian Departments to the danger of a transpacific raid, following the departure of the United States Fleet. The Chief of Staff and his advisers reasoned that, as collaborators with Nazi Germany, Japan and the Soviet Union might launch such a raid in an effort either to keep the United States Fleet in the Pacific or to block the Panama Canal after its passage into the Caribbean. They feared a raid against Hawaii only if the fleet had departed, and when President Roosevelt decided in early July to keep the fleet at Pearl Harbor their apprehensions about Oahu faded.21

The alert message to Oahu was plain spoken:

Immediately alert complete defensive organization to deal with possible trans-Pacific raid to greatest extent possible without creating public hysteria or provoking undue curiosity of newspapers and alien agents. Suggest maneuver basis. Maintain alert until further notice. Instructions for secret communication direct with Chief of Staff will be furnished shortly. Acknowledge.22

General Herron reacted with vigor. He ordered a 24-hour manning of all observation posts and antiaircraft batteries, and for the first time the antiaircraft gun crews received live ammunition and instructions to fire on any foreign planes sighted over restricted areas. Airplanes at Hickam and Wheeler Fields were dispersed, and on 21 June Army planes took over the task of inshore dawn patrols from the Navy. Although not similarly alerted, Admiral Richardson's forces co-operated wholeheartedly, instituting both inshore patrols and a limited amount of longer range aerial reconnaissance the limiting factor being the small number of Navy planes available for the purpose. On inquiry, the Chief of Naval Operations confirmed that the Army's alert had been issued after consultation with the Navy and requested Admiral Richardson to continue his co-operation. On 19 June the War


Department authorized a gradual modification of the alert, and a month later its relaxation at General Herron's discretion, except for continued precautions against sabotage and local air patrols on a training basis. The Navy maintained some distant patrolling by Oahu-based sea planes for most of the time until 30 December 1940, when Admiral Richardson discontinued such reconnaissance after being advised by the Chief of Naval Operations that only naval operating areas needed reconnoitering.23  In the meantime, the alert measures had fostered closer co-operation between Army and Navy forces, and in General Herron's opinion had had a wholly salutary effect on the morale of Army troops. In a personal letter of 6 September he told General Marshall that "the position of this place on the Army priority lists is still all right," and assured him that "as things now are, I feel that you need not have this place on your mind at all." 24  But on the preceding day he had officially asked for a good many more antiaircraft troops to man guns already on hand.

The request of Hawaii for more antiaircraft troops reached Washington in the same month that the United States Government openly shifted its course from neutrality to nonbelligerency and determination to support Great Britain in the Atlantic war. To be effective the new course required peace in the Pacific area, outside of China. But President Roosevelt and his advisers believed that the United States must also do what it could, short of war, to show Japan that its open alignment of 27 September with Germany and Italy was not going to stop American aid to Britain. As one gesture the President directed that Hawaii be reinforced by a National Guard infantry division, and Secretary Stimson had some difficulty in persuading the President that under existing circumstances such a move would really weaken and not strengthen the military security of Oahu. Partly to satisfy the President's wishes for some sort of reinforcement, as well as General Herron's plea for more men, General Marshall decided to send a National Guard antiaircraft regiment from California to Hawaii as soon as possible. The 251st Anti­aircraft Artillery Regiment, which moved to Oahu during the winter, was the first National Guard unit to leave the continental United States for overseas duty in World War II.25


With strength to man existing ground defense equipment in the offing, General Herron appears to have been reasonably well satisfied with the Army's posture of defense on Oahu in late 1940. During November he sent to Washington a paper entitled Draft Surmises on Insular Operations, his opening surmise being that fleets could not operate more than 2,000 miles from a major base, although a small raiding force could range much farther. The implication for Hawaii was that a small raiding force was all that need be anticipated. The general recognized the need to detect a carrier raid as far off as possible and acknowledged that a shore-based aerial patrol was a necessary adjunct to insular defense. But long-range reconnaissance was the Navy's business, as Admiral Richardson had informally acknowledged in August.26  And the discontinuance of Navy long-range patrolling by shore-based planes at the end of the year appears to have passed unnoticed by the Army.

The absence of an effective shore-based aerial patrol seems to have concerned General Herron much less than the prospective congestion of the air and of airfields when the Army and Navy obtained the full quota of planes that had been allotted to Oahu. The general wondered whether it might not be better to keep most of the heavy planes allotted to Hawaii on the west coast, on the assumption that the time had come when the Hawaiian Islands could be largely defended by bombers based on the mainland. The War Department thought differently, considering the 68 Army heavy bombers allotted the minimum needed on the spot; and it also took note of and advised General Herron about the Navy's new plan to station 180 long-range patrol planes in the islands, including 108 that were to remain permanently to patrol coastal waters and sea lanes. This last increment, when it arrived, could presumably provide all of the long-range reconnaissance needed.27  According to his later recollections, what worried General Herron most at the end of 1940 was the inadequacy of his antiaircraft defenses, not the present or prospective means of locating and bombing carriers. He told the Army Pearl Harbor Board in 1944 that he and his air commander had known "that an air force could come in and do some damage." Continuing, he said:

We hoped to be able to follow them out and destroy the carriers. But I do not think we had any idea that we could turn back an aerial attack entirely, for this reason: that


the only antiaircraft we had was that which was prepared against high-altitude bombing. We did not have the small-caliber stuff which you need to do anything about dive bombings. So we felt they could come in; that they would not come in there unless they had enough planes to overcome what planes we had.28

Defense Preparations During 1941

From available evidence it appears that as the year 1940 ended the Navy was more concerned than the Army about the state of the Army's defenses in Hawaii. After Admiral Richardson discovered on a Washington visit during October that the President was determined to keep the fleet at Pearl Harbor, he arranged with General Herron to inspect the Army's defenses and review their adequacy to protect the fleet and naval installations. His findings became the basis for a letter from the Secretary of the Navy to the Secretary of War on 24 January 1941, which stressed that Japan might initiate hostilities by a surprise attack on the fleet and on the base installations at Pearl Harbor, and envisaged an air attack by bombers and torpedo planes as more probable than threats of sabotage, submarine attack, the sowing of mines, and bombardment by naval gun fire. The Navy's estimate did not even mention invasion as a danger, though that was the preoccupation of a large portion of the Army defenders. The Navy urged "that the Army assign the highest priority to the increase of pursuit aircraft and antiaircraft artillery, arid the establishment of an air warning net in Hawaii." 29

The Navy's letter arrived on the heels of a forecast by President Roosevelt that Japan might even then be preparing to strike at the United States, and his decision that if that happened the United States must "stand on the defensive in the Pacific with the fleet based on Hawaii" and continue aid to Britain.30  The War Plans Division recommended that a few B-17's be sent to Oahu at once and that Hawaii (as well as Alaska and Panama) be put on a war basis as soon as possible.31  Even so, the War Department had drafted a routine response to the Navy's letter, stating in effect that nothing more could be sent to Hawaii for some time to come. General Marshall stopped this draft, and arranged to have eighty-one pursuit planes, fifty of them of the P-40B type, shipped by carriers- to Oahu as soon as possible.32



TROOPS ON MANEUVERS IN HAWAII, 1941, PREPARE TO RESIST INVASION. Guarding a beach (top). Loading a 75-mm. gun (bottom).



The Army answered the Navy's letter on 7 February 1941, the same day that General Herron relinquished command of the Hawaiian Department to Lt. Gen. Walter C. Short. A week earlier the Navy had reshuffled its forces, redesignating the fleet at Pearl Harbor as the Pacific Fleet and giving it a new commander, Admiral Husband E. Kimmel. The Army command went to General Short because of his reputation as an effective training man, and he threw himself into the work of his new post with great energy. General Marshall pointed out to him in a personal letter of 7 February that "the fullest protection for the Fleet is the rather than a major consideration" for the Army in Hawaii, and observed further:

My impression of the Hawaiian problem has been that if no serious harm is done us during the first six hours of known hostilities, thereafter the existing defenses would discourage an enemy against the hazard of an attack. The risk of sabotage and the risk involved in a surprise raid by Air and by submarine constitute the real perils of the situation. Frankly, I do not see any landing threat in the Hawaiian Islands so long as we have air superiority.

He also stressed the need for the closest co-operation with the Navy and with the new Navy commander, Admiral Kimmel.33

For various reasons, concern in Washington over the possible imminence of war with Japan subsided after February 1941, and worries over recognized deficiencies in the Army's defense equipment faded once more into the background.

By April, it looked as if the United States was on the brink of open participation in the Atlantic war, and plans were afoot to reinforce the Atlantic Fleet by withdrawing a substantial part of the Pacific Fleet from Hawaiian waters. In the eyes of Washington, Oahu looked more secure than ever, now that it was protected by some modern Army pursuit craft and was about to be reinforced further by fifty-five more P-40's and thirty-five B-17's. General Marshall assured Secretary Stimson that he thought Oahu was impregnable whether any fleet was there or not, because "with our heavy bombers and our fine pursuit planes, the land force could put up such a defense that the Japs wouldn't dare attack Hawaii, particularly such a long distance from home." 34

To assist Mr. Stimson in convincing the President it was safe to shift American naval power to the Atlantic, General Marshall had the War Plans Division prepare an estimate, the draft of which read:

The Island of Oahu, due to its fortification, its garrison, and its physical characteristics, is believed to be the strongest fortress in the world.


It has been carefully fortified against naval attack and its antiaircraft defense is relatively complete.

Its total garrison is at present approximately 31,000 men, and is in process of augmentation by 6,000 men.

Including the movement of aviation now in process, it is defended by 35 of our longest range bombers, 35 medium range bombers, 105 of our high speed pursuit ships, 65 fighters, and 13 light bombers.

The Hawaiian Islands are subject to (a) sabotage, (b) carrier raids, (c) an attack in force.

In point of sequence, sabotage is first to be expected and may, within a very limited time, cause great damage. On this account, and in order to assure strong control, it would be highly desirable to set up a military control of the islands prior to the likelihood of our involvement in the Far East.

Carrier raids by the Japanese involve jeopardizing naval units that will not be lightly undertaken. To meet these carrier raids our bombardment, protected by pursuit aviation, the latter operating from advanced fields on the Islands of Hawaii and Kauai, can cover a radius from Oahu of approximately 400 miles and beyond suitable points for the establishment of hostile land-based aviation.

An attack in force against Oahu necessitates an air superiority that can only be had by the establishment of land-based air within striking distance of Oahu. This can only be accomplished successfully within the Hawaiian group and with the defense indicated above it is not believed that such establishment can be accomplished.

Hawaii is capable of reinforcement by heavy bombers from the mainland by air.35

A note (by the President's military aide) on a revised version handed to Mr. Roosevelt summed up the War Department's optimistic view: "Modern planes have completely changed situation as to defensibility." 36  The principal effect of these arguments seems to have been to plant a new legacy of confidence among Washington leaders in the immunity of Hawaii from serious attack, since the President decided then and thereafter that the bulk of the Pacific Fleet must remain in the western Pacific as a deterrent to Japanese aggression.37

When General Short surveyed his new command in February 1941, he recognized a good many more flaws in its armor than the War Department in Washington did two months later. Although he appears never to have been greatly concerned during 1941 about the number of Army aircraft on hand and ready for action, he did take an intense interest in other matters related to air defense. Prompted by General Marshall's personal letter of 7 February and an official War Department communication of the same date, General Short turned his attention at once to improving co-operation


between Army and Navy forces and in particular to clarifying the respective responsibilities of their air forces in defensive operations.38

At the beginning of 1941 Army and Navy forces in Hawaii, as everywhere else in the field, operated more or less independently of each other, with co-ordination as circumstances required under the principle of mutual co-operation. On paper responsibility for local naval defense measures except aboard ship rested with the commandant of the Fourteenth Naval District, Rear Admiral Claude C. Bloch, and it was with Admiral Bloch's organization that the Army command proceeded to negotiate on a number of matters pertaining to air defense. Actually the Fourteenth Naval District had no defense forces of its own during 1941, and the contribution that the Navy could make to local defense depended upon what could be spared from the fleet and its Marine Corps attachments. It therefore depended also on the maintenance of a close personal relationship and understandings between General Short and Admiral Kimmel, the fleet commander.

Their predecessors, General Herron and Admiral Richardson, had succeeded in overcoming some of the characteristic resistance to effective Army-Navy co-operation in the field. An aftermath of the spring maneuvers and subsequent alert of 1940 had been an informal joint agreement on air operations under which the Navy assumed exclusive responsibility for distant reconnaissance, both services retained the right to conduct close-in reconnaissance for their own protection, and each might engage independently in air attacks against a hostile fleet.39  The new formal agreement signed by General Short and Admiral Bloch on 28 March 1941 left responsibility for distant reconnaissance with the Navy, but if Army planes helped out they were to operate under Navy command; if Navy planes helped in the defense of Oahu's land area, they were to operate under Army command; and any Army bombardment planes engaging in offensive operations at sea were to be under Navy command.40  In joint exercises during 1941 the new agreement worked well enough; but the prejudice in both services against unity of command offered fair assurance that except in such exercises the agreement would not be invoked unless a compelling and clearly recognized emergency was at hand.

In another joint paper signed three days later, the Army and Navy air commanders in Hawaii acknowledged how difficult it might be to foresee


such an emergency. Their estimate of the outlook emphasized the possibility of a sudden Japanese attack on Oahu prior to a formal declaration of war, and they noted the likelihood under existing circumstances that a dawn air attack launched from carriers might hit at the fleet and naval installations at Pearl Harbor with such complete surprise that defending pursuit could do little to soften the blow. They recognized that distant air reconnaissance was the best defense against surprise. Pointing out that it would be impossible with the equipment at hand to maintain such reconnaissance except for a short period, they emphasized the necessity of obtaining intelligence that a raid on Oahu was imminent before undertaking a systematic long range reconnaissance of its sea approaches.41

In addition to pushing toward agreement on other matters of mutual concern to the two services, General Short made a point of cultivating the personal friendship of Admirals Kimmel and Bloch. In forwarding the items described above to General Marshall, he stated that he had found both admirals most co-operative and that they all felt that steps had already been taken to make it possible for Army and Navy forces to act together and with the unity of command that the situation might require. Somewhat later Admiral Kimmel reported to Washington in the same vein, but noted the serious need for a great many more Army heavy bombardment planes.42

Instead of receiving 35 B-17's as planned in April, only 21 made an historic mass flight from California to Oahu in mid-May. The critical outlook of affairs in the Atlantic area induced General Marshall to withhold the other 14.43  Early in July the War Department was wondering whether more than one 35-plane group of heavies was really needed in Hawaii before the outbreak of a war, and even the Hawaiian Air Force commander optimistically estimated in August that one such group would be strong enough to finish off six enemy carriers. The real need, he felt, was for long-range reconnaissance; and, ignoring the Navy's responsibility for this function and plans for undertaking it eventually, he asked for a total of 180 heavy Army bombers so that the Army could do it. His request, warmly endorsed by General Short, reached Washington in the midst of new War Department planning that allotted from 136 to 204 heavy Army bombers to the Hawaiian


Department by mid-1942, and this planning had to suffice as an answer for the time being. These plans also coincided with the new Washington decision to reinforce the Philippines, and the net result was that Oahu lost 9 of its 21 heavies to the Philippines in early September and kept the remaining 12 only because they could be employed most usefully at Hickam as sources of spare parts and in training new combat and ferry crews.44

Superficially, Oahu's needs for pursuit craft appeared much better met. During most of the time between May and December 1941 it had about 150 Army pursuit and fighter planes, two-thirds of them modern P-40's. But a chronic shortage of spare parts kept many of these planes out of commission, and the ones available had to be used intensively for training. The greatest qualification was that pursuit planes, however modern, were all but worthless as defense equipment in the absence of an effective warning system, and Oahu had none before the attack on Pearl Harbor.45

In early December 1941 the Army did have an aircraft warning system nearing completion in Hawaii, but it was not yet in operation. This system depended for its information on the long-range radar machines developed by the Signal Corps in the late 1930's, the SCR-270 (mobile) and SCR-271 (fixed). The Signal Corps in Washington drafted the first plan for installing some of this equipment in Hawaii in November 1939, but before 1941 not much actually was done to prepare for its installation.46  As of February 1941 the War Department expected to deliver radars to Hawaii in June and hoped they could be operated as soon as they were delivered. The first mobile sets actually reached Hawaii in July, delivery having been delayed by about a month because of a temporary diversion of equipment to an emergency force being prepared for occupation of the Azores. In September five mobile sets began operating at temporary locations around Oahu, and a sixth, the Opana station at the northern tip of Oahu, joined the circuit on 27 November. Three fixed sets also arrived during November, but their mountain-top sites were not ready to receive them.47


The radars in operation on Oahu in late 1941 had a dependable range of from 75 to 125 miles seaward. An exercise in early November demonstrated their ability to detect a group of carrier planes before daylight 80 miles away, far enough out to alert Army pursuit planes in time for the latter to intercept incoming "enemy" bombers about 30 miles from Pearl Harbor. But this test in no way indicated the readiness of radar to do its job a month later. The sets were being operated solely for training; a shortage of spare parts and of a dependable power supply made it impracticable to operate them for more than three or four hours a day; the organization for using their information was a partly manned makeshift operating for training only; and defending pursuit, even if they could have been informed, would have had to keep warmed up and ready to take off in order to intercept enemy planes before they reached their targets.

The radars were not supposed to function except for training purposes until the Signal Corps turned them over to an air defense or interceptor command, to be operated by the Army pursuit commander through an information center which would receive data from the radar stations, warn the defending pursuit, control the movement of friendly planes, and control the firing of all antiaircraft guns. In March 1941 General Short had agreed that Hawaii needed such a command, and he arranged for his pursuit commander and his Signal Corps officer to visit the continental United States in the late fall of 1941 to witness operations and exercises of interceptor commands, preparatory to installing the system in Hawaii. They did not get back to Oahu until 4 December, much too late to get a local interceptor organization and information center into operation before the Japanese attacked.

The Army generally had more confidence in late 1941 in a much older weapon, the antiaircraft gun, as a means of air defense. Antiaircraft artillery had played an important part in the defense planning and preparation of the Hawaiian Department since 1921, when it organized the first antiaircraft artillery regiment in the United States Army. Twenty years later the latest revision of the Hawaiian defense project, approved by the War Department in September 1941, prescribed an impressive allotment of antiaircraft artillery weapons: 84 mobile and 26 fixed 3-inch guns for high altitude firing, and provision for replacing some of them as soon as possible with more modern weapons; 144 of the newer 37-mm. automatic weapons; and 516 caliber .50 antiaircraft machine guns for action against low-flying aircraft. By then also the department had four antiaircraft regiments, and it was scheduled to receive a fifth before the end of the year. Actually three


of the four regiments present were at little more than half strength, and the equipment on hand was considerably less than that allotted, amounting to 60 mobile and 26 fixed 3-inch guns, only 109 antiaircraft machine guns, and only 20 of the 37-mm. automatic weapons.48

With the strength available, Army antiaircraft on Oahu had the ability when deployed to give some protection against high-flying horizontal bombing planes along the south coast (from Diamond Head to west of Pearl Harbor) and around Schofield Barracks and Wheeler Field. The 37-mm. guns had been in Hawaii for almost ten months before ammunition for them arrived on 5 December 1941, and there had been very little for the antiaircraft machine guns, so that firing practice for even the small number of guns available for defense against dive or torpedo bombers or other low-flying planes had been more or less out of the question. About half the mobile 3-inch guns were assigned action stations on private property, and in practice sessions during the months before the Japanese attack the gun crews kept to nearby roads and carefully refrained from trespassing.49 Except during practice sessions the guns and the regiments that manned them were concentrated in three areas some distance from their battle stations, and at all times after May 1941 ammunition for the guns remained in the Ordnance depot. Only the fixed 3-inch guns, with ammunition boxed but close at hand, were ready for near immediate action. The rest depended on getting several hours' advance warning of an impending attack.

When General Short assumed command in February 1941 he immediately recognized the need for giving greater protection to Army aircraft on the ground by constructing dispersal runways and bunkers at existing airfields, and by building new airfields on Oahu and on other islands to relieve the congestion and close concentration of planes at Hickam and Wheeler Fields. By May the War Department had given formal approval to the construction to 253 bunkers, but it failed to provide any funds or to approve plans for them before the Japanese attacked in December. During the summer General Short by using troop labor managed to construct 85 bunkers at Wheeler Field; but under the alert of 27 November planes were ordered to be bunched not dispersed, and the bunkers therefore were not put to use.50


On Oahu during 1941 the Army completed and opened the new Bellows Field on the coast east of Honolulu, and it was being used in the fall by pursuit and light bomber planes. General Short wanted to build another pursuit field on the plateau about four miles northeast of Schofield Barracks, but the War Department insisted that it be located on the northern tip of Oahu, at Kahuku Point, instead. Because of this argument, and the fact that the Kahuku site was being used by the Navy as a bombing range, a new major pursuit field on Oahu remained no more than an idea before December.51  A small training field, near Haleiwa in the same area, was unknown to the Japanese and almost untouched by them in the Pearl Harbor attack. The Army also made arrangements with the Navy for the practice use of each other's airfields on Oahu and on other islands of the Hawaiian group, and for the extension of runways on Navy fields to accommodate Army heavy bombers.52

The development of military airfields in the outer islands harked back to plans of the 1920's and 1930's for the establishment of air bases on Hawaii and Kauai. Fields on these and other islands were begun in June 1940 by the Works Progress Administration in accordance with priorities established by the Army. A year later the War Department approved new construction that would allow the operation of heavy bombers from two fields on Kauai and three on Hawaii and would permit pursuit planes to operate from fields on Molokai and Lanai. Completion of these projects would make possible the distant dispersion of bombers from Hickam, and pursuit ships could be flown to the nearest islands. But no Army aircraft had occupied the new fields before 7 December.53

The beginnings of military airfield construction on other major islands, together with General Short's concern about the possibilities of sabotage or other hostile action by residents of Japanese descent, prompted the first garrisoning of the Hawaiian group as a whole by active Army forces. In May 1941 General Short detached the 299th Infantry Regiment from the Hawaiian Division and sent one battalion to Hawaii, another to Kauai, and divided a third between Maui and Molokai.54  These detachments and other Army forces sent to the outer islands were put under the local command of


military districts (of Hawaii, Maui, and Kauai) which in turn reported directly to the commander of the Hawaiian Department. Trained combat troops on the outer islands numbered about 1,300 at the beginning of December 1941.55

About the same time that General Short decided to garrison the outer islands he asked the War Department to approve the reorganization of the Hawaiian Division by distributing its four infantry regiments between two new triangular divisions. The actual reorganization, into the 24th and 25th Infantry Divisions, did not become effective until 1 October 1941. The new divisions had an authorized strength of about 11,000 officers and men each, but their actual strength was considerably less at the outset, and the 24th Division had no control over the battalions of the 299th infantry scattered among the outer islands.56

In the year preceding the Pearl Harbor attack, the Army's officer and enlisted strength in the Hawaiian Department grew from 28,798 to 43,177, and Hawaii remained the largest of the overseas garrisons.57  Nearly half the increase represented increments, including a good many men of Japanese descent, drawn from the local population through the induction of the National Guard and the operation of the selective service system.58  Since most of the new men received from the mainland also needed more training, the Hawaiian Department of necessity became a training establishment on a large scale during 1941, resembling in many respects the ground and air training commands then so active in the continental United States.

Until 28 May 1941 the RAINBOW plans contemplated an Army wartime garrison of 79,000 for Hawaii, substantially less than had been scheduled for it in war plans of the mid-1930's.59  On that date the War Department ordered a further reduction of 21,000 and lessened the decrease only slightly to accommodate General Short's plan for additional units to guard the Navy's new air station at Kaneohe Bay on the northeast coast of Oahu.60  By 22 September 1941, when Secretary Stimson and General Marshall went


over the strengths of all overseas garrisons with President Roosevelt, Hawaii had its full authorized peacetime strength of about 42,000. They agreed that any further reinforcement of the Hawaiian garrison could be deferred as long as the fleet remained in the Pacific, since the presence of the fleet reduced the threat of major attack.61  The revised RAINBOW 5 plan of November 1941 called for 17,300 more troops to be sent as war reinforcements as soon as possible, and an ultimate war garrison of about 68,000.62  Behind all these figures appears a confidence in Washington during 1941 that Hawaii by comparison with other overseas outposts was well manned, and that in the event of war Hawaii would not be on the front line of conflict as forecast by the larger war garrisons planned for it by the Army during the 1930's.

The same confidence can be deduced from war plans drafted and approved by the War Department during late 1941. Back in August 1937 Army and Navy planners had put the Hawaiian Coastal Frontier into Category of Defense D, which indicated an area that might be subject to major attack and within which all elements for defense should be approximately ready for action or in action, including an active antiaircraft gun defense of important areas and long-range aerial reconnaissance as required. Actually this provision meant very little either before or after the Pearl Harbor attack, since even after the attack the Category D description remained unchanged until October 1943, and at no time did it reflect with any accuracy the current status of defense operations. The War Department's RAINBOW 5 Operations Plan, approved 19 August 1941, confirmed Category of Defense D, and stated the Army's mission to be: "Hold Oahu against attacks by land, sea, and air forces, and against hostile sympathizers. Support naval forces in the protection of the sea communications of the Associated Powers and in the destruction of Axis sea communications by offensive action against enemy forces or commerce located within tactical operating radius of occupied air bases." 63  The provision for the support of naval forces was inapplicable until the Navy put its operating plans based on RAINBOW 5 into effect, an action which it did not take except in areas many thousands of miles from Hawaii until after the Japanese attacked. A month later, on 17 September, the War Department approved the latest revision of the


Hawaiian Defense Project, which listed the forms of possible enemy attack in the following order of probability:

(a) Submarine-torpedo and mine.
(b) Sabotage.
(c) Disguised merchant ship attack by blocking channels, by mines, or by air or surface craft.
(d) Air raids, carrier based.
(e) Surface ship raids.
(f) Major combined attack in the absence of the U.S. [sic] Fleet.64

Thus, sabotage was again confirmed as the principal and immediate concern of Army defense forces. Finally, in the revision of RAINBOW 5 completed in November, the Washington planners limited the sea area required for the defense of Oahu to a 500-mile radius from land, a limitation which if it had been applied would have confined long-range reconnaissance to bounds that all previous studies had considered ineffective for detecting the approach of carrier forces before they could launch their planes.65

Thus, though extensively reinforced, the Army defenses of Oahu were not ready by 7 December 1941 to detect the approach of a carrier attack or to cope with an air attack as powerful as that launched by the Japanese.


page created 30 May 2002


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