Battle For Okinawa: World War II | home
The sooner the Americans come, the better...
One hundred million die proudly.
- Japanese slogan in the summer of 1945
"In addition to U.S. casualties, the Japanese on Kyushu would likely have suffered upwards of 2,000,000 military and civilian casualties. These projected figures for Kyushu far exceed the casualties inflicted by the atomic bombs dropped on Hiroshima and Nagasaki, which ended the War with Japan. "
"Japan was finished as a warmaking nation, in spite of its four million men still under arms. But...Japan was not going to quit. Despite the fact that she was militarily finished, Japan's leaders were going to fight right on. To not lose "face" was more important than hundreds and hundreds of thousands of lives. And the people concurred, in silence, without protest. To continue was no longer a question of Japanese military thinking, it was an aspect of Japanese culture and psychology. "
James Jones, WWII
Japanese Homeland Defense Strategy
With the greater part of Japan's troop strength overseas and industrial production suffering under constant American air attacks, the defense of the Japanese home islands presented an enormous challenge to the Japanese Imperial General Headquarters (IGHQ). On 8 April 1945, the Imperial General Headquarters issued orders, to be effective 15 April, activating the First and Second General Armies.(1) These two Armies would be responsible for the ground defense of the Japanese home islands. Also, on 8 April 1945, IGHQ issued an order activating the Air General Army, effective 15 April.
The purpose of the new Air General Army was to coordinate the air defense of Japan, providing a single headquarters through which cooperation with the ground forces and the Navy could be expedited in implementing the defense of the home islands.(2) Simultaneously with the activation of the First and Second General Armies and the Air General Army, IGHQ issued orders for the implementation of Ketsu-Go (Decisive) Operation. Defensive in nature, the operation divided the Japanese home territory into seven zones from which to fight the final decisive battles of the Japanese empire.(3)
The strategy for Ketsu-Go was outlined in an 8 April 1945 Army Directive.(4) It stated that the Imperial Army would endeavor to crush the Americans while the invasion force was still at sea. They planned to deliver a decisive blow against the American naval force by initially destroying as many carriers as possible, utilizing the special attack forces of the Air Force and Navy. When the amphibious force approached within range of the homeland airbases, the entire air combat strength would be employed in continual night and day assaults against these ships. In conducting the air operations, the emphasis would be on the disruption of the American landing plans. The principal targets were to be the troop and equipment transports. Those American forces which succeeded in landing would be swiftly attacked by the Imperial Army in order to seek the decisive victory. The principal objective of the land operation was the destruction of the American landing force on the beach.
Ketsu-Go operation was designed as an all-out joint defense effort to be conducted by the entire strengths of the Army, Navy and Air Force. In the various orders and directives issued by IGHQ regarding Ketsu-Go, inter-service cooperation was stressed.(5) The basic plan for the operation called for the Navy to defend the coasts by attacking the invasion fleets with its combined surface, submarine, and air forces. The Air General Army would cooperate closely with the Navy in locating the American transports and destroying them at sea. Should the invasion force succeed in making a landing, the Area Army concerned would assume command of all naval ground forces in its area and would exercise operational control of air forces in support of ground operations. An integral part of the Ketsu-Go operational planning included reinforcement of sectors under attack by units transferred from other districts.
Since U.S. air raids had already seriously disrupted the transportation system, time schedules were planned to provide for all troop movements to be made by foot.(6) If the battle at the beach showed no prospect of a successful ending, then the battle would inevitably shift to inland warfare; hence, interior resistance would be planned. Guard units and Civilian Defense Corps personnel, with elements of field forces acting as a nucleus, would be employed as interior resistance troops. Their mission would be to attrite the Americans through guerrilla warfare, espionage, deception, disturbance of supply areas, and blockading of supplies when enemy landing forces advanced inland. It is interesting to note that the Japanese normally exercised little inter-service coordination throughout the war. Now when the homeland was threatened, the Japanese finally stressed inter-service coordination and unity of command.
Operational preparations for Ketsu-Go were conducted in three phases. The first phase, during which defensive preparations and troop unit organization was completed, continued through July 1945. The second and third phases were never completed because of the end of the war. However, the second phase, during which training was to be conducted and all defenses improved, began in August and was intended to continue through September. The third phase, which would see the completion of troop training and deployment, as well as the construction of all defense positions, would be completed during October.(7) Thus, if implemented, X-Day would have occurred just as Japanese defense plans had been completed.
For Operation Olympic, American forces would have landed against elements of the Second General Army. The defensive zone of the Second General Army was the western portion of Honshu and the islands of Shikoku and Kyushu. Within three days of being activated, on 18 April 1945, the Second General Army established its permanent headquarters in Hiroshima.(8) The Second General Army commanded the Fifteenth and Sixteenth Area Armies (equivalent to a U.S. field army). The seven defensive zones established for Ketsu-Go all had individual defensive plans. The defense of the island of Kyushu came under operation Ketsu-Go, No. 6. While Kyushu previously fell within the Western Military District, under Ketsu-Go, No. 6 the defense of Kyushu became the responsibility of the Sixteenth Area Army under the Second General Army.
The Second General Army estimated that the U.S. would enlarge its foothold on Okinawa, establish air bases on that island and, as soon as possible, begin its thrust at the Japanese archipelago via southern Kyushu. It was believed that the first objective of the Americans would be to secure operational bases for its Navy and Air Force. The Japanese correctly estimated that the American objective would be to secure Kagoshima Wan for anchorage and port facilities necessary for the buildup.(9) The earliest possible time at which an invasion attempt might be made by the U.S. was estimated to be the first part of July, when it was estimated that a strength of ten divisions could be mustered.(10) By July, Japanese officers were assessing that the invasion would occur in October or November 1945 due to the summer typhoon season.
The intent of Ketsu-Go was to inflict tremendous casualties on the American forces, thereby undermining the American people's will to continue the fight for Japan's unconditional surrender. This intent is clear in a boastful comment made by an IGHQ army staff officer in July 1945:
We will prepare 10,000 planes to meet the landing of the enemy. We will mobilize every aircraft possible, both training and "special attack" planes. We will smash one third of the enemy's war potential with this air force at sea. Another third will also be smashed at sea by our warships, human torpedoes and other special weapons. Furthermore, when the enemy actually lands, if we are ready to sacrifice a million men we will be able to inflict an equal number of casualties upon them. If the enemy loses a million men, then the public opinion in America will become inclined towards peace, and Japan will be able to gain peace with comparatively advantageous conditions.(11)
It is evident by this statement that in the summer of 1945 Japanese strategists identified the will of the American people as the U.S. strategic center of gravity and a critical vulnerability as the infliction of high casualties.(12)
Defense of Kyushu
The completion of defensive preparations in Kyushu was of the greatest urgency as the initial U.S. attack was almost certain to be directed at that island. Its defense was also the most difficult of all the districts, as Kyushu had the greatest length of vulnerable sea coast to defend.(13) Since it was generally conceded that the U.S. would make initial landings in Kyushu, the Sixteenth Area Army had been given priority in the receipt of supplies and in the build-up of troop strength. Fortification construction had also been emphasized and, in general, preparations were further advanced in Kyushu than in other areas of Japan.
Ketsu-Go Operation, No. 6 was the overall guide for the defense of Kyushu, but the Sixteenth Area Army prepared its own detailed defense plan. Known as the Mutsu Operation, the Army's plan divided Kyushu into three sectors which were, in turn, broken down into seven sub-divisions.(14) The Sixteenth Area Army estimated that the main American landing effort would be directed against the southeastern coast near Miyazaki, with secondary assaults anticipated to be made at Ariake Wan and along the southwestern coast at Fugiachi Hama on the Satsuma Peninsula. (see Map 9) Mutsu Operation No. 1 was given priority over the other operations. The Japanese thus were extremely accurate as to the location of the American landing zones.
Deployed throughout Kyushu and on adjacent islands, the Sixteenth Area Army had three armies and two special forces with a total of 15 divisions, 7 independent mixed brigades, 3 independent tank brigades and 2 fortress units. For a complete listing of Japanese units, commanders, and strengths on Kyushu see Appendix D.
The defensive concept called for each army to hold one division in reserve. In the event of an invasion, the Sixteenth Area Army would concentrate a force composed principally of the armies' reserve divisions and the three tank brigades. This force would then be utilized as an assault group to be rushed to the area of the main American effort. Their mission would be to annihilate the American forces as soon after the initial landings as possible. The defensive plan called for a major counterattack to be delivered within two weeks of the initial American landings.(15) As stated by a Japanese officer, the object of the defense was "to frustrate the enemy's landing plans with a counterattack like an electric shock, and at the proper moment to annihilate the enemy by close-range fire, by throwing hand grenades, and by hand-to-hand combat."(16) Groups assigned to coastal defense were to contain the enemy, while reserve troops were being concentrated for the decisive battle or, in some cases, hold out for long periods of time until a decisive battle was won in some other area and permit the release of strength for a counterattack in the sector being held.(17)
Having no way to counter U.S. air power, every effort would be made to confuse the battle lines so as to prevent the use of naval gunfire and air power to support the ground troops. The advances of the mobile reserves would be accomplished under cover of darkness for protection from aircraft.(18)
The defense positions in Kyushu were built in accordance with the precepts laid down in The Three Basic Principles on How to Fight Americans, which had been developed as a result of lessons learned in south Pacific combat. In brief, these principles were:
- Positions should be constructed beyond effective range of enemy naval bombardment.
- Cave type positions should be constructed for protection against air raids and naval bombardment.
- Inaccessible high ground should be selected as protection against flame throwing tanks.(19)
The production, movement and distribution of supplies was one of the most important aspects of the defense preparations on Kyushu.(20) Preparations included the storing of munitions in caves and other underground shelters to protect them from air raids and naval bombardment.
The original Japanese plan called for the supplying of each division with one campaign unit of fire, and by July 1945 this quantity was actually in the possession of the area armies. One campaign unit of fire was sufficient ammunition for one campaign - generally understood to be a three month supply.(21) This called for the following rounds per weapon: 1,000 rounds per field piece, 25,000 rounds per machine gun, and 240 rounds per rifle.(22) However, by August 1945 with the greatly increased number of troops, it was necessary to reduce ammunition stocks to a one-half unit of fire for each unit (about 1 1/2 months). This reduction in ammunition supplies made it necessary to adjust supply plans for the high priority areas and to plan for the rapid transfer of ammunition from one area to another when the invasion was actually launched and the place and direction of attack had been determined.(23)
The Japanese were preparing and may have been able to bring their ammunition supplies back up to the three month level given the amount of time between August and November.
Air operations against American landings on Kyushu were to be the responsibility of the 5th Naval Air Fleet and 6th Air Army, both under the control of the Air General Army. They had airfields throughout Kyushu, Shikoku and Chugoku. Fields in southern Kyushu which were being attacked almost daily had been abandoned as bases and were only to be employed for staging suicide missions.
Their plan called for the neutralization of as many transports as possible as the American fleet approached the shores of Japan. If landings were made, the air forces would conduct operations to sever supply lines to facilitate the fighting of the ground forces. Planes were to be released in waves of 300-400, at the rate of one wave per hour, against the invasion fleet. Sufficient fuel had been stored for this use, but only about 8,000 pilots were available.(24) Although the pilots were poorly trained and no match against experienced American pilots, they were capable enough to carry out suicide attacks against ships.
At the end of the war, Japan had approximately 12,725 planes. The Army had 5,651 and the Navy had 7,074 aircraft of all types.(25) While many of these were not considered combat planes, almost all were converted into kamikaze planes. The Japanese were planning to train enough pilots to use all of the aircraft that were capable of flying.
Naval operations against the invasion fleet would be conducted in two phases. The first phase would consist of attriting the American fleet as it approached the home islands. The remaining 38 Japanese fleet submarines would attempt to attrite as many transports as possible. They were to serve as launch platforms for manned suicide torpedoes called "Kaitens".
(Below: Two Examples of Kaitens Captured by the Americans after the war)
Although the Kaitens had not proved too successful in operations on the open ocean, the Japanese hoped that they would be effective in the restricted waters around the home islands.
The five-man midget submarines, known as "Koryu," would also be employed with either two torpedoes or an explosive charge for use in a suicide role. The Navy planned to have 540 Koryu in service by the time of the invasion. A more advanced midget submarine, the "Kairyu," was a two man craft armed with either two torpedoes or an explosive charge. Approximately 740 Kairyu were planned by the fall of 1945.
As the invasion fleet reached the landing areas, the second phase would commence. The 19 surviving Japanese destroyers would attempt to attack the American transports at the invasion beaches. Suicide attack boats, called "Shinyo," carrying 550 pounds of explosives in their bows, would strike from hiding places along the shore. The Shinyo were aiming for any craft carrying troops.
The Japanese Navy and Army had an estimated combined total of 3,300 special suicide attack boats. Finally, there would be rows of suicide frogmen called "Fukuryu" in their diving gear 30 feet or so beneath the water. The outermost row of Fukuryu would release anchored mines or carry mines to craft that passed nearby. Closer to shore, there would be three rows of divers, arrayed so that they were about 60 feet apart. Underwater lairs for the Fukuryu were to be made of reinforced concrete with steel doors. As many as 18 divers could be stationed in each underwater "foxhole".(26) Clad in a diving suit and breathing from oxygen tanks, a Fukuryu carried an explosive charge, which was mounted on a stick with a contact fuse. He was to swim up to landing craft and detonate the charge. The Navy had hoped for 4,000 men to be trained and equipped for this suicide force by October.
Ground operations against the American landings called for the ground forces to quickly determine the area of the invasion and concentrate in this area as many troops as possible before the invasion began. If the preliminary bombardment or early seizure of small islands to the south and southwest of Kyushu indicated an invasion attempt on southern Kyushu, then the 57th Division, the 4th Independent Tank Brigade, and the Chikugo and Higo Forces would move south to the vicinity of Kirishima to stage for a counterattack against the American landings.(27) The main body of infantry were to be deployed on the first commanding ground inland from the beach. These ground forces were to conduct operations so as to destroy the American forces in coastal areas before they secured firm beachheads. Should the Americans advance simultaneously in several locations, the ground forces were to direct the main operation against the main enemy force. If the enemy's main force could not be located, then the Japanese would seek a decisive battle in an area where their main force could most easily be directed. In the other operational areas, elements would carry on delaying actions in order to facilitate the operations of the main Japanese force.(28)
Medium and heavy artillery were to cover the landing craft approaches, the beaches, and plains areas surrounding the beaches. Plans for the employment of artillery seemed to combine the beach defense tactics employed on Saipan with some of the fixed defense plans employed on Iwo Jima.(29) Coastal defense and artillery batteries were to withhold their fire until landing craft came in range. However, there was no centralized control or fire-direction of the coast defense and artillery batteries.(30) The Japanese considered the massing of fires a waste of ammunition. Each artillery position was to remain in place conducting fires independently until destroyed. Artillery and mortar units were to be emplaced generally on the reverse slope of the first ridges inland from the beach and in caves further inland. The priority for employment of mortars was beach defense.
Commanders were told to be ready to swiftly divert the necessary troops and military supplies to other sectors at any time. The ground forces were to be concentrated in planned operational areas. Movement of ground forces would be primarily at night by foot, and the movement of war supplies would be by rail or water as the situation permitted. Troop movements were to be executed even under American air attacks.(31)
Coastal Defenses / Fortifications
The Japanese had extensive experience with how the Americans conducted amphibious assaults in the Pacific. In late 1944, the Japanese also sent a team of officers to debrief the Germans on their defenses at Normandy and how the Allies assaulted to gain a foothold in Europe. From these experiences the Japanese coastal defenses on Kyushu were divided into three zones.
1. Beach Positions - These positions were to be used mainly in beach fighting and for firing against landing craft. They were to be heavily fortified and concealed for protection against naval gunfire. Coastal fortifications were constructed in cave type shelters to withstand intense bombings and bombardments, especially from naval gunfire. They were to have the ability to conduct close range actions and withstand attacks from flame-throwers, explosives, and gas. Their purpose was to defeat any landing attempt.
2. Foreground Zone - If the beach positions could not prevent a landing, then the attack was to be delayed in this zone with localized counterattacks and raids. Obstacles, hidden positions, timed land mines, and assault tunnels utilizing natural terrain features were prepared to slow the attack and to fight within the enemy lines to limit the effectiveness of naval gunfire and close air support.
3. Main Zone of Resistance - This zone was the area where the main resistance was to be established. Battalions and larger units would occupy key terrain positions which were independent of each other. (see figure 12.) These positions were to be organized mainly for antitank warfare and the fields of fire were to be short. These installations were constructed as underground fortresses capable of coping with close range actions in which flame-throwers, explosives, and gas would be used.
This resistance zone was intended to stop the American advance and set up the major counterattack that was to decisively defeat the attack.(32) The Japanese paid special attention to camouflage of their positions even during construction.(33) Defensive positions were to be concealed from air, land, and sea observation. Within all three zones, dummy positions were constructed for deception. Cave installations were to be heavily reinforced and capable of withstanding a direct hit by naval gunfire. Pillboxes, assault positions, sniper positions, and obstacles were to be organized for close quarter combat and mutually supporting. Each position was to store water, ammunition, fuel, antitank weapons, food, salt, vitamin pills, and medical supplies.(34)
Defensive measures taken inland included Rear Defense Zones. These zones were established in important areas inland as alternate positions for the area army to be used in holding out against a forceful penetration by the enemy or in support of a strategic offensive.(35) Holding positions were constructed across lines of communications to check rapid advances of enemy mechanized forces.
Inland fortifications were also constructed to provide cover and concealment for heavy equipment such as tanks, motor vehicles and artillery as well as bomb proof storage of ammunition and fuel. As on many islands throughout the Pacific, these storage shelters were impervious to American air and naval bombardment.
Satsuma Peninsula Defenses (40th Army)
Mutso Operation, No. 1 covered the defense of southern Kyushu by the 40th and 57th Armies. This part of Kyushu was considered the most probable area to be invaded. Part C provided for the defense of the Satsuma Peninsula region by the 146th, 206th, and 303rd Divisions, and the 125th Independent Mixed Brigade of the 40th Army. In the event of an invasion in this area, those units would attempt to hold the V Amphibious Corps on the beaches until the mobile reserve could be assembled and moved from their inland locations. The counterattack phase would be carried out by a mobile reserve composed out of the 25th, 57th, 77th and 216th Divisions, together with the three tank brigades. The mobile reserve would advance to the vicinity of Ijuin to seal off the Satsuma Peninsula and prepare for the counterattack. There were also plans to redeploy two divisions from the Fifteenth Area Army in Honshu to augment the counterattack in southern Kyushu.(36)
The Japanese 40th Army had a strong concentration of artillery and heavy mortars on the western side of Satsuma Peninsula, south of Ijuin, in the 206th Division's zone of action. This concentration was closer to Fukiage Hama than to the beaches selected for the V Amphibious Corps.(37) Many units of the 40th Army were considered in poor state of organization and training. The 303rd and 206th Infantry divisions were particularly poor.(38)
The 77th Division, rated as A-1 by the Japanese, was under administrative control of the 40th Army and was held in reserve north of Kagoshima Wan. It was to be prepared to support the 40th Army if a landing were forced on the western shore of Satsuma Peninsula. The plan called for movement, chiefly by foot and at night, along the shore road of Kagoshima Wan, crossing the peninsula on the road system just west of Kagoshima. The estimated time for this movement was six to seven days.(39)
The 25th Division, also rated A-1 by the Japanese and under administrative control of the 57th Army, was held in reserve in the area of Miyakonojo. It was prepared to counterattack in the Miyazaki area. It likewise was to be moved chiefly on foot at night, the estimated movement time being five days.(40)
The 216th Division was centrally located in reserve at Kumamoto, prepared to move south as the situation dictated. If the preliminary bombardment or early seizure of small islands to the south and southwest of Kyushu definitely indicated an early invasion attempt on southern Kyushu, the 216th Division was to be moved, principally on foot and at night, to the area of Kirishima, northwest of Miyakonojo. This movement would have taken 7 days.(41) Likewise, if early indications pointed toward the invasion of southern Kyushu, the 57th Division and 4th Independent Tank Brigade of the 56th Army were to be withdrawn from the Fukuoka area and moved by any and all methods available to the Kirishima area.(42)
The defensive plan called for the use of the Civilian Volunteer Corps, a mobilization not of volunteers but of all boys and men 15 to 60 and all girls and women 17 to 40, except for those exempted as unfit. They were trained with hand grenades, swords, sickles, knives, fire hooks, and bamboo spears. These civilians, led by regular forces, were to make extensive use of night infiltration patrols armed with light weapons and demolitions.(43) Also, the Japanese had not prepared, and did not intend to prepare, any plan for the evacuation of civilians or for the declaration of open cities.(44) The southern third of Kyushu had a population of 2,400,000 within the 3,500 square miles included in the Prefectures of Kagoshima and Miyazaki.(45) The defensive plan was to actively defend the few selected beach areas at the beach, and then to mass reserves for an all-out counterattack if the invasion forces succeeded in winning a beachhead.(46)
The Japanese were determined to fight the final and decisive battle on Kyushu. At whatever the cost, Japanese military leaders were planning to repel any U.S. landing attempt. The defense of the Japanese home islands centered on two primary operations: the Army's fanatical defense of the beaches, and the employment of Kamikaze planes and suicide boats against transports. The Japanese plans for suicide attacks were much more extensive than anything the U.S. had yet experienced in the war. The Japanese special suicide forces were seen as a "Divine Wind" which was to save their nation just as the "Divine Wind" had driven the Mongol hordes back in the thirteenth century.(47)
1. Department of the Army, Office of the Chief of Military History, Homeland Operations Record, Japanese Monograph No. 17, (October 1945), 55.
2. ibid., 59.
3. ibid., 65. As early as mid-1944 the Japanese had initiated staff exercises labeled "Hypothetical Defense of Kyushu."
4. ibid., 205. Directive No. 243.
5. ibid., 66.
6. ibid., 67.
7. ibid., 105.
8. ibid., 100. At 0810 on 6 August, the atom bomb was dropped on Hiroshima, destroying the headquarters of the Second General Army and killing 80 staff officers.
9. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945,
10. Department of the Army, Office of the Chief of Military History, Homeland Operations Record, Japanese Monograph No. 17, October 1945, 101.
11. Weintraub, The Last Great Victory, 127.
12. Carl von Clausewitz, On War (New Jersey: Princeton University Press, 1984), 92.
13. Office of the Chief of Military History, Japanese Monograph No. 17, 65.
14. ibid., 126.
15. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 11.
16. War Department, Military Intelligence Division, Japanese Defense Against Amphibious Operations. Washington DC, February 1945, 1.
17. Office of the Chief of Military History, Japanese Monograph No. 17, 157.
18. ibid., 127.
19. ibid., 105.
20. ibid., 132.
21. ibid., 136.
22. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 16.
23. Office of the Chief of Military History, Japanese Monograph No. 17, 137.
24. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 10.
26. Allen and Polmar, Code-Name Downfall, 238.
27. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 16.
28. Office of the Chief of Military History, Japanese Monograph No. 17, 209.
29. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 14.
30. ibid., 11.
31. Office of the Chief of Military History, Japanese Monograph No. 17, 212.
32. ibid., 160.
33. ibid., 158.
34. ibid., 161.
36. ibid., 130.
37. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 12.
38. ibid., 18.
39. ibid., 15.
42. ibid., 16.
43. ibid., 13.
44. ibid., 30.
45. Commander Amphibious Force Pacific Fleet (ComPhibsPac), Annex C - Intelligence Plan, No. A11-45,10, August 1945, 3.
46. V Amphibious Corps, Appendix 3 to Annex C, Operation Plan, Occupation of Japan, 30 November 1945, 17.
47. Hatsuho Naito, Thunder Gods, The Kamikaze Pilots Tell Their Story (New York: Kodansha International, 1985), 24.