The
High Cost of Faulty Intel
(Page 2)
Naval History, February 2005
How Intelligence Influenced the Campaign
According to the JICPOA, 13,500 Japanese were on Iwo Jima.
Even though aerial reconnaissance indicated a massive build-up through
the fall and into the early winter of
1944, analysts claimed
that, "[T]here [were] no indications that the garrison [had] been reinforced."
6
In reality, about 23,000 Japanese occupied the island.
7
This gross underestimation skewed the entire intelligence report concerning
enemy capabilities, because analysts based other estimates on the number
of enemy soldiers they assumed occupied the objective.
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COURTESY OF THE AUTHOR, GRAPHICS
ENHANCEMENT BY FAITH STEWART
Marine Corps map of Iwo Jima drawn following U.S. occupation indicates
the extent of the Japanese defenses.
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By scrutinizing photos, analysts discovered only 105 major weapon sites,
including antiaircraft (AA) and dual-purpose guns, and 119 hardened weapon
positions, including pillboxes and covered artillery. But they knew the
Japanese would defend Iwo from more than just 224 weapons positions. After
all, it was one of the last outer defenses of the home islands.
Accordingly, since observed intelligence showed only part
of the Japanese defenses, analysts relied on reported intelligence to
fill the gaps.
8 Observed intelligence included things
analysts could see on a targeted island, and reported intelligence consisted
of things analysts hypothesized were on a targeted island. In the case
of Iwo Jima, the captured order-of-battle documents from Saipan led analysts
to hypothesize that certain Japanese units occupied the objective. In
turn, this led them to consult Japanese unit wire diagrams for information
on how many men were in each unit, and how many and what types of weapons
they had.
After considering reported defenses, analysts believed that in January
1945, the Japanese on Iwo possessed the following weapons: up to 39 artillery
pieces of 75-mm or larger, 24 70-mm howitzers, 18 mortars ranging from
81- to 240-mm, 10 80-mm naval guns, up to 54
AA guns with
another possible 33 "other AA guns," 42 to 54 37- or 47-mm anti-tank guns,
six rocket launcher positions, and 40 tanks.
9 Presumably,
these made up the bulk of Japanese artillery and support weaponry.
By February, Marine intelligence had increased many of these estimates.
10
The number of artillery guns had risen 100%. The number of coast defense
and dual-purpose guns had risen by 100% and 162%, respectively. Japanese
AA guns had risen by at least 41%. On the other hand, anti-tank (AT) weapons
had decreased by 83%, and machine guns had decreased by
17%.
Analysts said that there had been an 87% decrease in open artillery positions
and assumed that this was because they were moved into concrete and steel
fortifications, which had also increased.
11
Even while these estimates indicated significant increases,
most of them fell short of the actual situation. In reality, the Japanese
had 361 artillery pieces of 75-mm or larger, 65 mortars of 81- to 240-mm,
33 80-mm naval guns, more than 200 20- to 25-mm AA guns, 69 37- or 47-mm
AT guns, 70 rocket launchers, and 22 tanks. They also possessed 12 massive
320-mm mortars and 94 AA guns of 75-mm or larger.
12
Marines also met more defensive structures than expected; the JICPOA's
pre-action report
hardly mentioned them. All over the
island, the Japanese had built blockhouses and pillboxes for machine guns
and artillery. The report asserted that analysts had observed only 39
pillboxes, 13 covered artillery positions with 4 under construction, and
about 170 "rifle pits."
13 The same report largely
neglected blockhouses, but the Marines' February
intelligence
report indicated 35 blockhouses on Iwo with 4 under construction. It also
said 332 pillboxes were on the island.
14 This was
an astounding increase of fortifications in the one-month time span between
reports.
When the battle ended and JICPOA and fleet intelligence units began their
analyses of the island's concrete and steel defenses, there were so many
they did not have time to plot them all on a map as they had in past campaigns.
Analysts were reduced to discussing numbers in broad terms. For example,
the JICPOA's 10 June 1945 Iwo Jima after-action intelligence report devoted
a whole section of its analysis just to blockhouses and pillboxes, thereby
indicating their abundance and successful employment
by the enemy. The same report stated that, while many pillboxes commanded
a scant 30° field of fire, "there was a sufficient number of mutually
supporting pillboxes to offset the restricted field of fire of each weapon."
15
What is more, Marines encountered numerous concrete fortifications in
a defensive zone they called the Meat Grinder. Located on the east side
of the island in the 4th Division's area of operations, it consisted of
three mutually supportive strongpoints: Hill 382, another hill
called
Turkey Knob, and a natural depression in the ground called the Amphitheater.
The Meat Grinder included hundreds of defensive structures, and its Amphitheater,
according to the JICPOA after-action report, "contained two terraces and
three tiers" of concrete fortifications.
16 Overall,
the JICPOA's after-action bulletin made 21 references to these defenses
in just five pages and summarized them in a separate, five-page, ten-photo
pictorial.
This also happened with tunnels and caves, many of which were natural,
but most of which seemed to be manmade. Pre-battle intelligence claimed
the Japanese would use caves to
shelter men and logistics
from bombardment. The JICPOA figured that the vast majority of caves on
Iwo were located on the northern end of the island. In contrast, the after-action
report stated "thousands of caves [were] used for defensive positions."
17 Indeed, most
caves on the island
housed guns and were nearly impervious to conventional infantry assault.
Caves were so numerous on Iwo Jima that intelligence analysts said "that
it was impossible to plot them all on a 1:10,000 map."
18
In the end, it summarized tunnels and caves in a four-page, 11-photo pictorial.
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COURTESY OF WORLD WAR II 50TH
ANNIVERSARY COMMITTEE
An armada of U.S. ships, including battleships firing 14- and 12-inch
guns, bombarded the landing beaches at Iwo Jima for several days,
trying to soften the enemy defensive positions before the Marines
landed.
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Terrain served the enemy in a capacity similar to caves, and analysts
barely mentioned it in pre-battle intelligence. It provided the Japanese
with excellent natural fortifications and slowed U.S. infantry movement.
Loose and deep sand between the western landing beaches and the
opposite
shore slowed tank and infantry traffic that made easy targets for Japanese
gunners and riflemen.
19
Similarly, the northern end of Iwo Jima did not contain many man-made
defensive structures, because its terrain was just as formidable as the
rest of island. Armed to the teeth, Japanese troops hid in every hole,
depression, and crevice. Where the terrain allowed, several enemy soldiers
clustered together in natural pillboxes and bunkers armed with machine
guns. In other instances, the Japanese embedded tank turrets into the
island's volcanic rock to serve as improvised blockhouses. Iwo Jima's
terrain also allowed for forward and reverse slope defenses on the same
ridgelines.
Notes:
6. JICPOA Information Bulletin 9-45, p. 2. [
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to article]
7. George W. Garand and Truman R. Strobridge, Western
Pacific Operations: History of U.S. Marine Corps Operations in World War
II, vol. 4 (Washington, DC: Historical Division, Headquarters Marine Corps,
1971) p. 458. [
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8. JICPOA Information Bulletin 9-45, p. 1. [
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to article]
9. JICPOA Information Bulletin 9-45, pp. 1-2, “Important
Errata Note,” p. 11, and map titled, “Military Installations and Estimated
Troop Dispositions of Iwo Jima (Sulphur Island).” [
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article]
10. It is unclear how involved fleet intelligence
was in the Iwo intelligence operation, or if the same rotation policy
that affected the JICPOA’s photo interpreters affected those of the fleet.
Regardless, it is evident fleet intelligence was not able to pick up the
slack where the JICPOA proved inadequate. [
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11. Headquarters, Expeditionary Troops, Task Force
Fifty-Six, State of Enemy Defenses, Iwo Jima, 13 February 1945, pp. 1-2.
[
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12. Garand and Strobridge, Western Pacific Operations,
p. 454. This chart does not include every weapon the Japanese had. They
also possessed three 20-mm mortars. [
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13. JICPOA Information Bulletin 9-45, 1, plus “Nearshore,
Beach, and Soil Conditions, Iwo Jima” map that includes minute detail
on Japanese defense installations. [
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14. Headquarters, Expeditionary Troops, Task Force
Fifty-Six, State of Enemy Defenses, Iwo Jima, 13 February 1945, p. 2.
[
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15. JICPOA Information Bulletin 136-45, Defense Installations
on Iwo Jima (Pearl Harbor, HI: 10 June 1945,) p. 5. [
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to article]
16. JICPOA Information Bulletin 136-45, p. 4. The
majority of Japanese concrete fortifications on Iwo were steel reinforced.
[
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17. JICPOA Information Bulletin 136-45, p. 19. [
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to article]
18. JICPOA Information Bulletin 136-45, p. 2. [
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to article]
19. The tactical battle data came from Bartley, Iwo
Jima: Amphibious Epic, Garand and Strobridge, Western Pacific Operations,
and the chapter on Iwo Jima in Jeter A. Isely and Philip A. Crowl, The
U.S. Marines and Amphibious War (Princeton, NJ: Princeton University Press,
1951). [
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