An Analysis of the 1944 Japanese Defense of Saipan
After the assault on Saipan the United States sent military scholars to study the Japanese defense of Saipan. The results of their analyses was incorporated into a series of lectures at the War College to brief American officers as to what they could expect from Japanese defenders on other islands as U. S. forces moved closer to the Japanese home islands. The content of these lectures has been condensed as is presented here-in. Sources: The Japanese Defense Of Saipan, Military Intelligence Service, War Department, January, 1945. and Target Survey
Saipan, 1944, Joint Intelligence Center, Pacific Ocean Area. Tanks: The proposed employment of Japanese tanks was to "destroy the enemy at the water's edge after nightfall". Their tank strength consisted of the 9th Tank Regiment of about 100 medium tanks. During the entire operation there were only two instances when the Japanese used tanks in comparatively large numbers. The first occurred during the early morning hours of June 17 when medium tanks approached in groups of four or five and upon reaching the U. S. position cruised up and down the front line and then overran the U. S. positions. Individual Marines crouched in their foxholes and slit trenches as the tanks rolled over them. As the tanks passed the Marines leaped from their foxholes and attacked the tanks with bazookas and anti-tank grenades. Incendiary grenades and demolition charges were dropped into disabled tanks. While U. S. 37 mm guns did not penetrate the turrets of the tanks they were effective against the bogie wheels and tracks, stopping them and enabling U. S. troops to destroy them with other weapons.
The second use of tanks occurred during the evening of June 23 and all the next day. During this period seven different tank attacks were made upon U. S. forces with a total of 36 tanks destroyed. The Japanese failed to support their armor attacks with the use of large numbers of infantry. They made too many separate attacks, thereby, enabling U. S. anti-tank weapons to destroy each group individually. In addition, their tanks were not properly deployed. Several times small groups of tanks attacked U. S. positions in a single file down a ravine or road from which no deployment could be made. They were easily destroyed by U. S. forces because they were unable to deploy when the lead tank was hit. In addition the Japanese frequently used tanks as fixed pillboxes. Supply System: Saipan was well supplied and equipped by the Japanese, yet there were many instances when its defenders were in great need of those very items which were in abundance. Since it was one of the major Japanese bases in the central and western Pacific, it was utilized as a supply and staging area for islands to the south.
Consequently, abundant quantities of materiel, food and equipment not only passed through its harbors but were stored ashore. Yet many drastic shortages became apparent as the campaign progressed. There were several reasons for Japanese deficiencies in the supply and distribution of equipment and rations. Surprisingly, they had not completed supply establishments adequate for operating under field conditions, even though a tremendous amount of food and equipment had been stored in caves prior to the attack on the island and probably still remains in many of the sealed caves. Additionally, U. S. naval gunfire, artillery bombardment, air strafing and bombing so upset all existing logistic plans as to cause a complete breakdown. The road network was denied the Japanese during daylight hours and to a lesser extent at night as well. Ammunition became a critical item at many front line positions, indicating that supply lines could not be maintained. Water supply points were destroyed, resulting in sever shortages. As supply trucks were knocked out the Japanese were forced to rely on small hand drawn carts and shoulder packs.
Furthermore, many supply depots were destroyed by the bombardment. American Command Conflict: During the fighting on Saipan a serious conflict erupted within the command of U. S. forces. This heated and dangerous controversy between two American generals, both of whom were named Smith, went unknown to the Japanese at the time.
Marine General Holland Smith decided to move three divisions along a line north to Mount Tapotchau, U. S. Army General Ralph Smith's 27th Division was directed to pass through the 4th Marine Division on the night of June 22nd and join the attack at the center of the line the next day. Concerned that his men might not be able to find their way in the darkness, General Ralph Smith delayed movement until daybreak. During the 7,000 yards uphill movement his men became disorganized and his attack fell behind schedule. The 27th was frequently delayed by well concealed Japanese machine guns. Such tactics as the Army employed irritated the Marines who felt that the Japanese should be pushed backward leaving little opportunity for the defenders to prepare fixed positions.
The Marines of the 2nd Division fought their way up the steep slopes of Mount Tapotchau under the hail of Japanese fire. The Army's 165th Infantry Regiment found it could not advance beyond a series of hills now known as Purple Heart Ridge, a name given an area on the eastern side of Saipan because of the heavy casualties inflicted on the Americans. During this period the advance of the Army's 106th Infantry regiment into an area which came to be known as Death Valley had also been slow.
In only two days of fighting in this sector, the Japanese had inflicted 1,145 casualties on the Marines as opposed to only 277 on the Army. It was believed at the time that the heavy casualties sustained by the Marines was partly the result of an all around poor performance and lack of aggressiveness on the part of the Army. This situation led Marine General Holland Smith to believe that an immediate change in command was necessary in the Army's 27th Division and that General Ralph Smith should be relieved of duty. The more serious of two charges made against the Army general was that on the morning of June 23rd the 27th Division had been from 55 minutes to 2 hours late in launching its attack and thereafter retarded the progress of the Marines on its flanks. U. S. Army General Ralph Smith was relieved of his command .
This dismissal of an Army general by a Marine general precipitated an inter-service controversy of alarming proportions which resulted in seriously jeopardizing harmonious relations at all levels among the Army, Navy and Marine Corps units in the Pacific. With still more than two weeks of fighting the Japanese ahead of the American forces, the relationship between top Army and Marine Corps officers reached the breaking point. The bad blood which developed between these two American fighting forces in the midst of the battle for Saipan reached such a point that it endangered future operations in the Pacific. Had the Japanese been aware of this inter-service conflict between the top American commanders they may have been able to exploit the situation to there advantage. They were, however, unaware of the imbroglio with the American command structure. Supplying The Invasion Force: The problems of supplying and replenishing the Saipan invasion force presented enormous logistical problems as war materiel of all types had to be transported from Hawaii and the United States west coast.
A special mobile service fleet of auxiliary vessels, including tankers, repair ships, food and ammunition, cargo vessels was established to service the warships enroute to the western Pacific. While the assault troops were at sea the Navy had to feed all personnel aboard ship and all Marines once placed ashore. A vessel with a capacity of 5,000 tons could carry 348,000 cubic feet of refrigerated cargo
enough food to feed 90,000 troops for one month. The huge Stores Issue Ships (AKS) carried 40,000 different items from dental equipment to government issued coffins.
Navy tankers transported the petroleum products which permitted aircraft to consume 8 million gallons of avgas. The aircraft carriers along burned 4. 5 million barrels of fuel oil. It remains a mystery why the Japanese did not concentrate their attack on these tankers rather than direct their attention, as they frequently did, to the troop carrying transports and combatant vessels. The fleet expended more than 6,000 14 and 16 inch shells; 19,000 rounds of 6 and 8 inch shell; 140,000 rounds of 5 inch shells and this does not include the ammunition expended by individual assault troops once ashore. It was not uncommon practice for some Marines to abandon their heavy backpack of supplies once they hit Saipan's beaches, keeping only their weapons.
When the time came to replenish their ammunition or K-rations they simply picked up what was needed from a dead Marine who had carried the added weight ashore. Air Operations: Once American landings occurred there was no report of Japanese aircraft operating from any of the three airfields on Saipan. All were rendered non-operational by the pre-invasion naval and air bombardment. Only Aslito field was used to any extent prior to the U. S. invasion While Aslito was a well equipped air base capable of receiving any type aircraft, it was used almost exclusively by fighters with Tinian as the location of the Japanese bomber command. Twenty four planes were captured on the ground at Aslito. The air strip near the beach at Chalan Kanoa was an emergency fighter strip and construction was only half completed. The strip at Marpi Point was also still under construction at the time of the attack.
The Japanese launched a total of 26 night air raids during the American assault phase with 14 planes shot down. The Japanese order of priority for targets was: (1) Aslito field once it fell to U. S. forces; (2) shipping located in the Chalan Kanoa area and (3) occasional supply areas and in one case American front line positions. Japanese Strategy: Although preparations for coast defenses had been accelerated, the Japanese forces were not well equipped at the time of the invasion. The total strength of the island has been estimated to be about 29,000 men, including 7,000 naval personnel and numerous miscellaneous units and transients mixed with the Japanese Army. At the time of the American attack, Saipan was still a staging area and a number of Japanese units had recently arrived without ammunition, weapons and supplies which had been lost at sea while enroute to Saipan as a result of U. S. submarine attacks.
After departing Saipan with 1,700 people, many of whom were employees and their families of the South Sea Development Company, the Amerika Maru was torpedoed on March 6, 1944. This same fate befell 1,500 troops of the Japanese 43rd Division enroute to Saipan in late May 1944, to strengthen General Obata's 31st Army. Defensive Terrain: Saipan's terrain is ideal for waging a defensive battle, but the Japanese high command apparently gave little thought to organizing its forces on the ground away from the beaches since very few permanent defenses were found inland, except those in caves and airfields.
Even Aslito field in the south was practically undefended against advancing ground troops. The island was divided by the Japanese into four defense sectors. Tank and artillery units were alerted to strike against landings on the west coast. Four Japanese infantry companies were designated as reserve and ordered to train principally in seaborne maneuvers presumably to execute counter landing operations against an American beachhead. Japanese Morale: There was no indication of low morale affecting Japanese combat efficiency which remained high to the very end. Early in the campaign, information was disseminated to the Japanese troops that the Imperial Japanese Fleet was on the way to give battle to the "American Devil” who had succeeded in planting his feet on "Imperial soil". When the fleet failed to appear, "news” was given out that the Japanese Navy had met the American Navy in a great sea battle and inflicted tremendous losses on it at small cost to the Japanese.
Such information gave great joy to the defenders of Saipan. However, it was not true. The Battle of the Philippine Sea known also as the "Marianas Turkey Shoot” on June 19, 1944 resulted in the loss of three Japanese aircraft carriers and 400 planes as opposed to the loss of only 58 U. S. aircraft.
It cannot be said that at the end of the Japanese resistance on Saipan morale had weakened to such an extent that it impaired combat efficiency. Quite the opposite in the words of General Saito, "Whether we attack or whether we stay where we are, there is only death, however, in death there is life". The Japanese were ready to attack fully realizing that death was to be the result. Coastal Defenses: At the time of the invasion very few of the island's permanent defense installations had been completed, though coast defense and anti-aircraft battery positions gave evidence of intensive preparation for attack. In many instances, casements, emplacements and magazines were less than half finished. Coastal defense guns placed in the sides of cliffs or on forward slopes were sited for flanking fire on possible landing beaches. Most gave attacking ground troops little trouble since many were either still under construction or were silenced by naval gunfire or aerial bombardment. In some cases camouflage concealed guns to such an extent that attacking aviators were deceived. Such examples included the three gun 140 mm battery on Naftan Peninsula and the reinforced concrete block-houses on the southern beaches and at Magicienne Bay all undamaged by naval gunfire or aerial bombardment. Painting on the sides and roof in addition to earth terracing on the sides between the gun embrasure contributed to the effectiveness of camouflage.
The three guns of the 120 mm battery in process of construction to cover the north east approaches to beaches at the Kagman Peninsula (Brown Beaches 1 & 2) had been concealed simply by covering the tubes and carriages with foliage. Nets employed by the Japanese to cover gun positions and ammunition storage pits were ineffective as no garlands had been woven into the nets. Artillery: The Japanese had the equivalent of seven experienced battalions of field artillery at the time of the attack. It has been estimated that the following guns were available for their use; eighteen 75 mm howitzers; seventeen 75 mm guns; sixteen 105 mm howitzers and twelve 150 mm howitzers. Artillery was sited to fire at focal points such as the harbor entrance, breaks in the reef line and beach areas. A number of pieces apparently were ranged independently on these areas and there is little to indicate that a common survey control or an elaborate communication system was utilized .
Once U. S. forces had established a beachhead, the Japanese showed little ability to deliver fire in directions other than along sight lines originally planned.
From D Day until June 18th the Japanese successfully employed their artillery against U. S. beachhead positions. they were located at positions on the reverse slopes of the high ground inland from the landing beaches. Five 150 mm howitzers, sixteen 105 mm howitzers and thirty 75 mm field pieces positioned in this area were partially responsible for the heavy casualties suffered initially by U. S. forces on the landing beaches. One thousand rounds had been fired from one battery alone. Although the Japanese had much artillery within range of the landing beaches, their failure to mass fire on U. S. landing craft and troops during the initial landings or in support of a strong counterattack during the next few days following the invasion is considered one of their major tactical errors. The fire delivered on the beaches and reefs on D day was sporadic, scattered and of a density which would indicate that not more than one battery fired on an area of target at one time. The gun at Naftan Point was operated from a cave with the entrance covered by steel doors. The gun would be run out, fired, and returned to the interior of the cave immediately after which the doors were closed.
Two 75 mm guns located in the vicinity of Mount Tapotchau were camouflaged during the day and fired only at dawn and dusk to prevent detection of flashes. The tactic was very successful and it took almost one week to locate the guns so they could be destroyed. Although the Japanese field artillery was mobile, the 75 mm pieces were moved only about 1,100 yards per day through mountainous terrain and about 4,400 yards a day over relatively level ground. The failure of the Japanese to use counter battery and long range destructive fire has no conclusive explanation. Their failure to make proper use of artillery contributed in great part to their defeat. Japanese Defenders: The Japanese defenders of Saipan were the victims of strategic surprise as well as the sheer power of American invading forces. The Japanese command was caught unprepared on June 15,1944 by American forces. Few Japanese battery positions and fortifications had been completed; beach defenses were not finished and several thousand Japanese troops were without arms and awaiting reorganization at the time of the invasion. During the first four days of the twenty five day campaign, Japanese artillery and mortar fire on the beaches and nearby areas exacted a heavy toll in casualties on the attacking U. S. forces. This situation soon changed under the weight of U. S. naval gunfire and aerial bombardment. By D day plus ten (June 25) the Japanese had lost Mount Tapotchau, the highest ground on Saipan at 1,545 feet and thereafter their situation was untenable.
From what can be learned from records of the period, the Japanese defense of the island was premised upon the denial of Tanapag Harbor to the landing forces as well as all the beaches on the east and south shores. They depended upon a mobile army force to defeat American troops landed elsewhere. This assumption is supported by the location of permanent coast defenses, dual purpose weapons, concrete blockhouses as well as the actions of the Japanese garrison once U. S. troops had landed on the beaches in the vicinity of Chalan Kanoa on the western shore. It appears that the original intention of the defending forces was to fight from prepared beach positions, supported by artillery and mortars. However, intense U. S. naval gunfire forced the Japanese to withdraw to the east. It soon developed that the Japanese alternative plan for defense against U. S. landings on the west coast was to withdraw initially from the beaches, to shell the beaches with all available weapons and then launch a coordinated counterattack before the American forces could consolidate their positions.
In following this course of action, the Japanese placed great reliance upon field artillery with their entire plan of defense aimed at destroying the U. S. landing force on the beaches. Their failure to do so resulted in their defeat and changed the course of history for Saipan. Mines: The Japanese made sparse use of beach obstacles and land mines and had not prepared defenses of the type on the western beaches, indicating that they were not expecting an attack from that direction. Inland mine fields were small, feeble and relatively ineffectual. They were armed with improvised munitions and were often poorly sited and ill concealed, thus reflecting little deliberate planning. Of the several different types of mines encountered on Saipan they were generally visible and no difficulty was encountered in disarming and removing them.
Deliberate mine fields employing the 60 kg. general purpose bombs were employed by the Japanese in the northern half of Saipan to cover their retreat and to harass the advance of U. S. armored units.
These fields lacked depth and density and were easily breached. Booby traps were employed in only a few places at ammunition dumps and on Japanese dead awaiting an unsuspecting souvenir hunter. Aircraft Defenses: Japanese AA artillery consisting mainly of the 25th AA regiment and naval AA units was weak during the battle for Saipan. Many hundreds of sorties were flown by U. S. aircraft without serious damage to the aircraft.
Comparatively few U. S. planes were shot down. It is believed that many Japanese AA positions were destroyed by U. S. naval artillery and air bombardment prior to and shortly after D day. The strong reliance by the Japanese on fixed anti-aircraft guns contributed largely to the ineffectiveness of their AA fire. Once a gun position was spotted it was almost certain that it would be destroyed or neutralized in a matter of minutes. From the number of guns found unplaced for firing, it is clear that the anti-aircraft defenses of the island had not been completed at the time of the invasion.
Though Saipan had been under Japanese control since October, 1914, the largest coast defense guns placed were obsolete six inch naval guns such as the one formerly located at Agingan Point and even the emplacements for these were incomplete. This six inch gun had been manufactured in 1900 by Armstrong-Whitworth for the Japanese Navy.
Many of the island's temporary oriental and occidental occupants were ground unto dust and baked in a cauldron of fire, steel and stone on Saipan. Deep inside the island's sealed caverns those Japanese that did not die of burns from phosphorus grenades lobbed through entrances to ignite oil which had been poured inside, succumbed to starvation, suffocation, concussion and utter depression. In the dark, damp interior of many of the island's sealed caves their remains disintegrated into dust entombed within the bowels of Saipan's brooding mountains. They are still there.
A Japanese Analysis of American Combat Methods
The following text was taken from a Japanese document captured in New Guinea. It was written by a Japanese divisional staff officer on 4 March 1943, and later distributed to the Japanese soldiers in the South and Southwest Pacific areas including Saipan. The English translation appearing here-on employs several American colloquialisms added by the translators with English words substituted for Japanese map symbols. Some charges were made in grammar, punctuation and spelling during translation. Except for the alterations noted above, the text of the publication is reproduced in English almost in full, without change. I Offense:
Fear In Combat:
The U. S. military conducted some unique research projects utilizing combat veterans of the south and central Pacific. One such study concerned fear in combat and informed 18 and 19 year old recruits that they would be frightened . "Before you go into battle, you'll be frightened at the uncertainty at the thought of being killed. Will it hurt? Will you know what to do? If you say you're not scared, you'll be a cocky fool. Don't let anyone tell you that you are a coward if you admit being scared'. This study, based on the experience of 2,095 combat veterans, reported the following percentage of occurrence of specific symptoms of fear in combat:
Violent pounding of heart 84%
Feeling faint or weak 49%
Sinking stomach feeling 69%
Feeling of stiffness 45%
Shaking & trembling 61%
Vomiting 27%
Sick stomach 55%
Losing control of bowels 21%
Cold sweat 56%
Urinating in pants 10%
Source: War Department Pamphlet 21-13,1944