NIDS Commentary No. 392 published by the National Institute for Defense Studies, Ministry of Defense on August 5, 2025, a military research analysis by Yuichi Shinfuku of the Center for Military History, International Conflict History Research Office, examining the tactical changes in the Japanese Army homeland defense preparations during the final stages of the Pacific War from a military perspective.
Background and Purpose of the Research
Eighty years ago, the Japanese Army opposed peace negotiations and advocated thorough resistance until the Emperor's sacred decision was made. The Imperial General Headquarters Army Department believed that while they had been defeated on small Pacific islands and in jungles where ground forces could not be concentrated, decisive battles would be possible on the homeland where forces could be concentrated. This operation was called "Operation Ketsu-Go."
There are two methods to prevent enemy forces from landing: "waterline annihilation," which involves direct deployment near the shoreline to deny the establishment of beachheads, and "coastal annihilation," which involves deployment away from the shoreline in coastal areas, temporarily allowing beachhead establishment but then concentrating forces to destroy them. After successful coastal annihilation tactics at Iwo Jima and Okinawa, the Japanese military ultimately returned to waterline annihilation for the homeland defense.
Progress of Homeland Defense Preparations
Since the garrison at Saipan Island, which adopted waterline annihilation in June 1944, lost most of its strength within about a week of the landing, the Imperial General Headquarters Army Department permitted garrison forces to defend from positions at appropriate distances from the waterline in terrain-strong locations. Subsequently, Peleliu Island and Iwo Jima, which adopted coastal annihilation, succeeded in inflicting unavoidable losses on U.S. forces.
From January 1945, the Imperial General Headquarters Army Department began full-scale homeland defense preparations and issued the Operation Ketsu-Go Preparation Guidelines in April. There were six expected American landing areas from Tohoku to southern Kyushu, with Kanto (Ketsu-3) and southern Kyushu (Ketsu-6) judged to have the highest probability of occurrence.
Transition Process from Coastal Annihilation to Waterline Annihilation
In February, Lieutenant General Shuichi Miyazaki, Chief of Operations at the Imperial General Headquarters Army Department, explained the coastal annihilation concept of "assembling 20 divisions within two weeks" and "dividing army operations into restraining armies and striking armies." This method involved setting positions "at appropriate rear locations from the coast" and concentrating forces within one to ten days to destroy beachheads.
However, Miyazaki considered the insufficient fortification, training, and supply of coastal blocking forces in Kyushu and Shikoku regions as problematic, and by May began reevaluating waterline annihilation methods. In June, he distributed "Quick Guide to Homeland Decisive Battle Tactics" to promote position setting for continued resistance at the waterline.
The decisive transition was the issuance of "Regarding the Thorough Implementation of Fundamental Principles of Homeland Decisive Battle" (Fundamental Principles) under the name of the Vice Chief of Staff on June 20. This completely shifted anti-landing operations to "thoroughly pursuing the enemy's inevitable weaknesses at the waterline" and "destroying them in the process before the enemy occupies bridgehead positions," denying beachhead establishment operations.
Analysis of Factors in Tactical Changes
Combat Effectiveness Perspective
Shortage of Tangible Elements: The homeland defense preparation units had insufficient firepower and mechanization, with the 36th Army conducting offensives having approximately 70% infantry troops, and most tanks being light tank class. Division rifle and machine gun sufficiency rates were around 40%, and about 70% for the entire 12th Area Army. Critical was the shortage of air power, as air support coordinated with army offensives and air defense could not be expected, making troop movement difficult without air superiority.
Intangible Element Issues: Cooperation between coastal blocking forces and offensive forces required "invincible confidence through meticulous training," but Kyushu's defense forces were "specialized in self-sufficiency with insufficient training and fortification," and regarding troop morale and discipline, "desertion and misconduct reached sixty percent." Mobilized units mainly consisted of reserve personnel and young soldiers, making agile actions according to operational command intentions difficult.
Characteristics of Anti-Landing Operations and Understanding of Battle Lessons
Response to Lack of Initiative: Anti-landing operations have the characteristic that the side waiting for landings becomes passive. Reflecting on repeatedly falling into passivity in previous island operations, the Japanese Army sought to regain initiative by preparing and implementing predetermined routes in advance.
Battle Lessons from Okinawa: An important factor in the Imperial General Headquarters Army Department's choice of waterline annihilation was reflection on the Battle of Okinawa. In Okinawa, the 32nd Army did not deploy on the expected landing front and did not counterattack during the U.S. landing, resulting in the bloodless occupation of North and Central airfields. Miyazaki criticized this as "suspicion of prioritizing passive self-preservation above all" and recognized that once beachheads were established, destroying landed forces would be nearly impossible.
Limits of Military Rationality
The Imperial General Headquarters Army Department ultimately chose waterline annihilation, recognizing that complex coordination attacks by mobilized forces with inferior firepower and equipment without air superiority would be difficult, simplifying forces into close-range assaults (essentially special attacks) to create close combat situations despite inferior strength, taking advantage of the fluid situation immediately after landing.
However, the problem was that while emphasizing the necessity of waterline annihilation, they shifted the problem of material shortages for executing waterline annihilation to local units' self-help efforts and invincible confidence issues. Without allocating concrete, rebar, or coastal fortification materials, they ordered the advancement of main positions to the waterline, forcing local units to set up positions on sandy beaches using wooden field fortifications.
The article concludes that while the Japanese Army's tactical changes were based on military judgment rather than mere spiritualism, there was a tendency to prioritize personal subjectivity over objective analysis-based rational judgment and a problem of failing to provide appropriate resource allocation to local units.