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
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
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
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.
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.
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.
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.