A U.S. intelligence report on the Japanese defense plans on Iwo Jima, from the Intelligence Bulletin, July 1945. [Editor's Note: The following article is wartime information on enemy weapons and tactics published for Allied soldiers. More accurate data on Japanese weapons and tactics is available in postwar publications.]

 

IWO JIMA WAS READY JAPANESE PLANS FOR DEFENSE Several months before the U.S. invasion of Iwo Jima, the Japanese were ready with a plan for each phase of a proposed defense. Applying many of the lessons they had learned on Saipan, Tinian, and Guam, the Japanese deviated from their former basic principle of small-island defense: "Annihilate the invaders on the beaches." Instead, the doctrine laid down for Iwo Jima—and apparently observed in most respects—included protection against preliminary bombardment, establishment of defensive positions in depth, coordination of the fire power of all units, and detailed antitank preparations. Map of Iwo Jima—The dark areas indicate the strongest defense zones, according to the Japanese plan. ORGANIZATION OF THE TERRAIN Organization of the island's defenses posed an immediate problem. The Japanese attempted to solve it by dividing their defensive set-up into three categories—main defenses, beach positions, and inner lines of defenses. The strongest positions on the island were to be constructed on a zone about 1,100 yards in depth, curving across the center of the island. The front edge of the zone would touch Motoyama Airfield No. 2. Other fortifications were to be built in the Mt. Suribachi sector, at the southern end of the island. The strongest positions in this sector were to be within a line 770 to 880 yards from the foot of the mountain, and strongpoints connected with the beach positions were to be prepared in the forward areas. In an attempt to defeat the invaders on the beaches, strong key positions were to be organized on the beaches, on both sides of Motoyama Airfield No. 1, and elsewhere. However, the perimeter defense, which had proved unsuccessful in previous island campaigns, was abandoned in favor of reliance on withering artillery fire. Major U.S. landings were anticipated on the southwestern and southeastern coasts. (Actually, they were made on the southeastern side of the island.) Since American landings also might be made in strength in the northern or eastern sectors, the enemy ordered the forces holding these sectors to be on the alert and to overwhelm any landing attacks. If necessary, reserve units in these sectors were to be committed to exploit the difficult terrain and halt U.S. advances by strong and determined counterattacks. At possible landing places in the eastern and northern sectors, independent positions in depth were planned, running from a line near the water's edge hack to the cliff area. In the interior, several positions which could interdict the main road network leading into the interior were to be established. The Japs were determined to have strong key positions at all strategic places on the island, if time permitted. They proposed to turn Iwo Jima into a virtual fortress by the gradual reinforcement and connection of these points. DETAILED BATTLE PLAN Thinking in terms of what conceivably might happen, the Japs planned the successive phases of their battle strategy as follows: To avoid excessive losses during preliminary bombing and bombardment: The defense commanders ordered their forces to resort to dispersal, concealment, camouflage, and maximum utilization of defense works. To defeat U.S. landing attempts: Maximum artillery fire coordinated with that of coastal-defense guns, as well as stubborn resistance for the beach positions, was ordered. U.S. tanks were to be destroyed by close-quarter attacks. To prevent U.S. expansion of a beachhead, if the landings succeeded: Artillery and infantry fire, raiding attacks, and other countermeasures were to prevent any expansion or consolidation of the beachhead and were to reduce U.S. battle strength. Primary targets would be command posts, artillery positions, and tank concentrations. To prevent penetration of the main defenses, if U.S. forces succeeded in expanding their beachhead: The attacks would be met with concentrated fire power, close-quarter attacks, and vigorous local counterattacks. To prevent capture of the main defenses, if U.S. forces succeeded in penetrating them: Counterattacks supported by fire power were to be launched. To defend the inner line of positions, if U.S. forces succeeded in capturing the main defenses: The Japanese commanders advised their troops to hold out as long as possible by carrying on stubborn resistance from a line of secondary defensive positions. If U.S. forces should succeed in capturing the inner line of positions: The Jap commanders admitted that at this point it would be difficult to continue organized resistance. They nevertheless urged all men to fight tenaciously and inflict heavy casualties on U.S. forces before succumbing. ANTITANK TACTICS U.S. forces would find it difficult to maneuver tanks on the sandy beaches, the Jap commanders decided. They believed that for this reason it would be most feasible to destroy the invading tanks by means of land mines, shelling, and close-quarter attacks. If U.S. beachheads were established, Jap raiding parties were to exploit the confusion resulting from artillery fire and darkness. If the battle drew close to the main positions, where the terrain and artificial obstacles might restrict the movement of U.S. tanks, it was the Jap intention to destroy the encroaching armor by means of antitank guns, a few Japanese tanks, and assaults by close-combat teams. The personnel of the close-combat teams were to be chosen expressly for this work. The construction of many antitank ditches and other tank obstacles, both outside and inside the positions, was recommended as the best means of reducing the mobility of U.S. tanks and facilitating close-quarter attacks. ARTILLERY DEFENSES In setting up their artillery defenses, the Japanese ordered that all artillery units be coordinated, and that fire concentrations be planned not only for the beaches, but for the areas in front of, and within, the main positions. Close cooperation between infantry and tanks also was ordered. Artillery fire was to begin when small U. S. craft reached the beaches. Targets in the water were to be fired on only by specifically designated forces. For surprise effect, the Japs ordered the use of "special-type weapons" (presumably their rockets and spigot mortars). Preparations were to be made against surprise night attacks and landings, as well as against airborne raiding units. USE OF TANKS To conserve their armor, the enemy commanders ordered that the tank forces be withheld during the opening phases of the battle. Japanese tanks were principally to be used in conjunction with the fighting around the main positions; however, elements were to support counterattacks in the eastern and northern sectors, should fronts develop in those areas. COUNTERATTACKS The Japanese commanders again broke away from the methods employed on other islands when they considered the execution of counterattacks. Because large-scale counterattacks not only had failed to accomplish the desired results in the past, but also had dangerously weakened the defending forces, the commanders ordered that all counterattacks be conducted by small forces only. Maximum fire power and thorough preparation were to be emphasized in planning counterattacks, which were to be carried out systematically. However, surprise attacks were not to be shelved; the enemy urged that these be used when troops could take advantage of darkness, terrain, or weather conditions, or when a local situation offered favorable opportunities. DEFENSE AGAINST PARATROOPS That the Japs feared paratroop landings on Iwo was also indicated in the plan, which included procedures for combating such attacks. Emphasizing the necessity for strict antiaircraft security measures, the Japanese ordered that the planes be fired on before the paratroopers jumped, and also directed that certain elements fire on these men as they descended. Stressing the point that the airborne troops should he wiped out before they had an opportunity to consolidate, the commanders not only arranged for artillery to deliver neutralization fire on the fields, but assigned forces to attack and destroy any U.S. troops who might reach the ground.

Back to Articles by Subject | Intel Bulletin by Issue | T&TT by Issue | Home Page