The Japanese defense of Guam was much less effective than that of Saipan. Not only did the Japanese have fewer men, less artillery, and fewer tanks than their compatriots on Saipan but they also had a much larger area of land to defend. Nevertheless, they had ideal terrain for the defense and a sufficient force to prevent a rapid or easy conquest of the island.
Guam’s defense was commanded initially by General Takashima, Commanding General, 29th Division and Southern Marianas Army Group. In the middle of June General Obata, Commanding General, 31st Army, reached Guam with his two senior staff officers. He had been in the Palaus, probably because the Japanese expected the next American thrust to be in that area. Once it became apparent that the blow would come farther north, he had hastened to the Marianas, too late, however, to reach his headquarters on Saipan. Instead, he landed on Guam to linger in forced inactivity while the garrison on Saipan went down to defeat. His presence on Guam had very little influence on Japanese tactics there until the death of General Takashima on 28 July, after which Obata assumed direct command.
Troops and Troop Dispositions
In mid-July, on the eve of the American invasion of Guam, the Japanese defenders numbered about 18,500 men. The early preponderance in air and naval strength that the Americans were able to establish in the area resulted in the loss to the Guam garrison of about 900 much needed men, including the 1st Battalion, 10th Independent Brigade. These troops had been temporarily stationed on Rota and on 8 June had been ordered to return to their parent commands on Guam. By the time the move could be organized, however, the 38-mile stretch of water between the two islands was under close American surveillance, and the transfer was never made.
Altogether, the American invaders faced an understrength garrison composed of eleven Army infantry battalions, two and two-thirds Army artillery battalions, three tank companies, two Army antiaircraft companies, Army engineers, service troops, and so forth, together with various Navy units, the most important of which were the 54th Naval Guard Force and the 60th Antiaircraft Defense Unit.
In early June these forces were spread all over the island as a precaution against an invasion from any direction. Guam was divided into four sectors for purposes of defense. In the Agana sector were stationed the four battalions of the 48th Independent Mixed Brigade and the 3rd Battalion, 38th Infantry; in the area around Agat were the 1st and 2nd Battalions, 38th Infantry; on the south coast in the Inarajan sector were two battalions of the 10th Independent Mixed Brigade; and in the northern sector, with headquarters at Finaguayac, was the 2nd Battalion, 18th Infantry.
[N4-16-3 TF 56 Rpt FORAGER, Incl D, G-2 Rpt, p. 47. The locations of the 3rd Battalion, 18th Infantry, and of the several naval units were unknown.]
By July this picture had radically changed. The American naval shelling of Agat on 16 June had tipped off the Japanese as to the probable place of the forthcoming landings, and the postponement of W Day gave them ample opportunity to reorganize their defenses. By mid-July almost the entire garrison had been moved to the west coast between Agat and Tumon Bay.
At the time of the American amphibious assault, Headquarters, 29th Division, and most of the division’s service troops were located at Fonte, as was the headquarters of the 48th Independent Mixed Brigade. General Shigematsu, Commanding General, 48th Independent Mixed Brigade, commanded the Agana sector, which stretched along the west shore from Piti to Tumon Bay and included the great majority of the Japanese forces on the island.
For purposes of shore defense, the Agana sector was divided into three, perhaps four, beach defense areas. From northeast to southwest, the first of these was at Tumon Bay, where the 322nd Independent Infantry Battalion was located. The 321st Independent Infantry Battalion defended the area around Agana Bay, and the 320th Independent Infantry Battalion manned the defenses between Adelup Point and Asan Point, where the 3rd Marine Division was to land. In the Piti area was the 18th Infantry Regiment, less the 1st Battalion, which was on Saipan. The unit was considerably understrength since some of its personnel and much of its equipment had been lost when one of its ships en route from Japan had been sunk by an American submarine. The 18th Regiment also had partial responsibility for Asan Point in case the Americans should land there.
The 10th Independent Mixed Regiment, less its 1st Battalion and 9th Company, was in the Fonte-Ordot area. The 319th Independent Infantry Battalion was inland, east of Agana, in reserve. Two of the three tank units on the island were also in reserve, poised to strike the beachhead with the infantry. These were the 29th Division Tank Unit at Ordot and the 2nd Company, 9th Tank Regiment, at Sinajana. Also in general reserve was the Otori Unit, composed chiefly of naval air personnel reorganized into a jerry-built unit for ground combat. Most of the Army artillery, including the 48th Independent Mixed Brigade Artillery Unit, formerly the 3rd Battalion, 11th Mountain Artillery Regiment, was disposed throughout the Agana sector.
The two batteries of the 10th Independent Mixed Regiment Artillery Unit had been removed from regimental control and placed directly under the 48th Independent Mixed Brigade. Certain guns of these batteries were located just inland of Tumon Bay, but the majority were in the vicinity of Agana. The 38th Infantry’s Artillery Battalion was broken up, one battery attached to each infantry battalion, so that the 3rd Battery, attached to the 3rd Battalion, was also in the Agana sector force.
The Agat sector was commanded by Colonel Tsunetaro Suenaga, commanding officer of the 38th Infantry Regiment, whose command post was on Mount Alifan. The 1st Battalion, 38th Infantry, covered the beaches in the Agat area, and the 2nd Battalion of the same regiment occupied the base of Orote Peninsula. To the rear of the Agat beaches, the 1st Company, 9th Tank Regiment, was in readiness to counterattack in case of a landing. Also in reserve for the Agat beaches was the 9th Company, 10th Independent Mixed Regiment.
Orote Peninsula was garrisoned by the main body of the 54th Naval Guard Force; the 755th Air Unit, reorganized for ground combat; and the two batteries of the 52nd Antiaircraft Artillery Battalion, which was charged with antiaircraft defense of Orote airfield. Since this unit’s guns, which were 75-mm. antiaircraft, could be depressed as low as minus seven degrees, they were in effect dual purpose and could be used to supplement the conventional field artillery and anti-boat weapons.
Other units, such as service, engineer, and construction units, were scattered throughout the island, some on the west coast, and some inland as far as Santa Rosa. None of these, however, had any significant combat value. Nor could the Japanese arm the civilian population, most of which appears to have remained at least passively loyal to the United States. As of 10 January 1944, the native Guamanians numbered about 24,000. Slightly over a hundred were of mixed American and Chamorro parentage and had been jailed as soon as the Japanese occupied the island. The rest of the population suffered some organized maltreatment and abuse in the early days of Japanese rule, but this appears to have gradually tapered off.
However, rigid food rationing, forced labor, confiscation of property without compensation, exclusion from business enterprises, and a score of lesser deprivations and humiliations kept the native population sullen and restive during the period of Japanese occupation. In June 1943 all able bodied men between the ages of fourteen and sixty were forced to work for the occupation army and women were ordered to replace the men in the fields. After the American air raid of 11 June, large numbers of natives fled to the hills. Many were rounded up by Japanese military police and placed in camps near Asinan, Manengon, and Talofofo. The Guamanians were clearly poor raw material for collaborationism, and there is no evidence that the Japanese made any successful attempt to reconstruct them to that end.
[N4-16-6 Sources for the description of the lot of Guam’s civilians under Japanese rule are William Hipple’s report in Newsweek, August 21, 1944, p. 35, and Thompson, Guam and Its People, p. 160.]
Japanese military doctrine for the defense of Guam was essentially the same as that for Saipan. Emphasis was placed on meeting and annihilating the enemy at the beaches. If that failed, an organized counterattack was to be delivered against the beachhead soon after the landing. Finally, if the invaders succeeded in establishing and holding their beachhead line, the Japanese would retire to the hills and fight on from there.
Thus General Shigematsu, in command of the Agana sector garrison unit, which contained the majority of troops on the island, declared on 15 July, “It has been decided that the enemy is going to launch an attack in force at dawn in the region of the Agana sector. When he lands, the Division will be quick to seize the opportunity to attack him in this sector with a powerful force and crush him at the beaches. . . . The Garrison Unit will await its initial opportunity and will completely destroy the enemy landing force upon the beaches.” If the infantry units at the shore line failed in their mission, the 10th Independent Mixed Regiment, two battalions of the 18th Infantry, and the 3rd Battalion, 38th Infantry, were ordered to carry out the second phase of the plan—a counterattack in force against the American beachhead in this area.
Artillery on Guam, including coast defense, field artillery, and antiaircraft and antitank weapons, was manned by both Army and Navy personnel. As indicated above, the bulk of the field artillery pieces in July were situated to command the western shore line from Tumon Bay to Agat. Table 2 gives two estimates of the number and type of these weapons. Just how many were still operational at the time of the American landings is not known, and even a comparison of these figures with the assessment of damage wrought by the preliminary bombardment cited above will provide only a hazy idea of Japanese artillery strength on 21 July.
Japanese tank strength was considerably lower than it was believed to be by American intelligence staffs, both before and after the battle. Although the Americans claim to have destroyed or captured fifty-nine enemy tanks by 11 August, actually there were no more than thirty-eight present at any time, and possibly even fewer. The 1st Company, 9th Tank Regiment, which was located in the Agat-Orote area, had from twelve to fifteen light tanks. The 2nd Company of the same regiment and the 29th Division Tank Unit, both situated so as to support the defense of the Asan beaches, had a total of from twenty-one to twenty-three tanks, of which at least ten were mediums.
The main fortified area ran along the west coast from Tumon Bay to Facpi Point and included, of course, Orote Peninsula. Other fortified beaches, on the south and east coasts from Merizo to Pago Bay, had been abandoned before W Day, their defenders having moved to the north. Outside the main fortified area, the airfields were provided local defense by antiaircraft and dual-purpose guns.
The most notable and certainly the most effective fortifications on the island were constructed across the neck of Orote Peninsula, which contained a fairly elaborate system of trenches and foxholes arranged in depth, together with large numbers of pillboxes and heavy-caliber weapons. Outside of Orote, the prepared defenses were generally hastily constructed and often incomplete. The typical beach defense was arranged, from the seaward side, in four parallel lines: first were obstacles and mines on the fringing reef offshore; second came beach obstacles and tank traps; third were trenches, machine gun positions, pillboxes, heavy weapons, artillery, and coast defense guns on the beaches or immediately inland; and, finally, came the machine guns, heavy weapons, and artillery emplaced on the high ground inland.
Insufficient advantage was taken of the high ground, and except on Orote little provision was made for defense in depth. Even as late as the five-week period of pre-invasion bombardment, the Japanese continued to work frantically on improving offshore obstacles and beach defenses, to the neglect of positions in the rear.
During the first two years of the war, the Japanese had slighted the military development of the Marianas in favor of more forward areas, and almost nothing was done to fortify Guam until early 1944. The beaches had to be protected first, and Guam’s large size and numerous possible landing points meant that proportionately greater effort had to be expended at the shore line before work could be commenced on defenses in depth. The time, effort, and materials expended on the south and south-east shores was ultimately wasted when these positions were abandoned. After the assault on Saipan, Guam was entirely cut off from its sources of materiel, and the five-week period of bombardment not only destroyed many of the existing fortifications but also severely hampered efforts on the part of the Japanese to continue construction.
As has been already mentioned, the Japanese relied heavily on coral-filled palm cribs and wire cages to interrupt and impede the approach of landing craft to and over the offshore reef. In addition to these, which were all blown up by American underwater demolition teams, a series of anti-boat mines of about forty to fifty pounds was placed along the reef or between the obstacles. The beaches themselves were strung with barbed wire and in some places aerial bombs were embedded in the sand just inland of the wire. Antitank obstacles also were installed on the beaches by lashing coconut logs across trees or setting them vertically in the ground.
The Agat beach defenses were typical of the others. Here was an almost continuous line of open trenches about two feet wide and three and a half feet deep. Running parallel to the shore line approximately fifty feet inland of the high-water mark, these trenches were supplemented by an occasional rifle or machine gun pit about eight feet to their front and by shelters to their rear. Distributed along the beach between Agat and Bangi Point were about twenty-five pillboxes. A strong concrete blockhouse on Gaan Point held two 75-mm. mountain guns, one 37-mm. gun, and positions for machine guns and riflemen. Two concrete emplacements of 40-mm. guns were located between Gaan Point and Agat only about five feet inland of the high-water mark.
Pillboxes here were constructed of palm logs, sandbags, reinforced concrete, earth, and coral rocks, the majority being simple structures of palm logs covered with earth. They averaged about eight feet square and three feet high, with roofs two feet thick in the center and one foot at the edge. Usually, they had two firing ports about twelve by four inches in size, which allowed only a fairly narrow traverse. The reinforced concrete types were either square or octagonal and located chiefly along the roads. About eight feet across and two to three feet high, their walls were about six inches thick. There were a few masonry pillboxes of coral rocks with walls a foot thick. All the pillboxes on the beaches were mutually supporting against attack from the seaward side, but not against attack from the flanks or rear.
Japanese Situation on the Eve of Battle The effects of American preliminary bombardment on Japanese defenses has already been described in as much detail as surviving records permit. The devastation was great and widespread, if not as effective as the invaders at first believed. Moreover, the accelerating tempo of naval shelling and aerial bombing and strafing made it almost impossible for the Japanese to repair the damage or to engage in new construction.
Notwithstanding these difficulties, the defenders bent every effort to shore up their crumbling defenses to the last minute before the invasion. But most of the labor, at least along the beaches, had to be performed at night when darkness and the physical exhaustion of the troops slowed progress to a snail’s pace. The dilemma was inescapable, as is attested by one Japanese Army lieutenant who complained, “Our positions have been almost completed but they have not been done as we had hoped . . . great effort was put into the construction but we still have been unable to complete the cover. We are in a terrible fix.”
[N4-16-13 Imanishi Diary; see also CINCPAC – CINCPOA Trans 10802, extracts from the diary of Corporal Suzuki, Tai; CINCPAC-CINCPOA Trans 10410, diary of an unidentified soldier.]
The weeks of American bombardment, the prolonged uncertainty, the anxious waiting from day to day while explosions rent the air but no American soldier came into view to be shot at or stabbed with bayonet—all these factors took their psychological toll even on the martial-minded Japanese. They suffered greatly in seishin —a word that means not so much “morale” as “psychological well-being.” After several days of successive attacks, “scattered outbreaks of serious loss of spirit” occurred. After another week the spirit of some of the men deteriorated so badly that they “could not perform their duties in a positive manner.”
This cumulative physical and psychological exhaustion would show up in the days of battle to come. The troops on Guam tended to become more easily disorganized than had their compatriots on Saipan and Tinian. They turned more readily from organized combat to futile and suicidal individual displays of fanaticism.
But if their seishin was ebbing, the Japanese on Guam remained high in shiki—meaning morale in the sense of a willingness to die in combat. This spirit is reflected, with the usual rhetorical flourishes, in the diary of one enlisted man: “I will not lose my courage, but now is the time to prepare to die! If one desires to live, hope for death. Be prepared to die! With this conviction one can never lose . . . . Look upon us! We have shortened our expectancy of 70 years of life to 25 in order to fight. What an honor it is to be born in this day and age.” Against this kind of determination, the task facing the marines and soldiers of the III Amphibious Corps would by no means be light.
SOURCE: Campaign in the Marianas; BY: Philip A. Crowl (United States Army Center of Military History)