On 19 February 1945, the U.S. Marine Corps launched one of history's bloodiest amphibious operations. The 3d, 4th, and 5th Marine Divisions, supported by hundreds of ships and tactical aircraft, battled for more than a month on Iwo Jima, an island two miles long and five miles wide. It was a ferocious fight that resulted in legendary feats of heroism. Marine and Navy casualties totaled 28,686, with 6,821 killed in action, one of the highest U.S. death tolls in the Pacific War.1 The Japanese made the battle tough with their expertly engineered defensive positions and fanatic refusal to surrender. But inadequate knowledge of the enemy's capabilities and intentions made it tougher. For Iwo Jima, U.S. intelligence underestimated the number of Japanese combatants on the island, their weapons, their defense, and the terrain they occupied.
The Joint Intelligence Center, Pacific Ocean Areas (JICPOA), was the main intelligence provider for the Iwo Jima operation. The military established it at Pearl Harbor's Makalapa Crater in September 1943 after nearly two years of merging smaller intelligence entities together and adding to them. With a staff of 1,767 Army, Navy, and Marine intelligence specialists, the center processed all-source intelligence from secondary-source research, reconnaissance photographs, enemy prisoner of war (POW) interrogations, captured documents, and enemy communications. In the last category, however, the JICPOA worked jointly with a U.S. Navy communications center called the Fleet Radio Communications Unit, Pacific (FRUPAC). Army Brigadier General Joseph J. Twitty served as the commander, and Navy Captain W. J. Holmes served as its second in command. The JICPOA's mission was to provide Admiral Chester Nimitz, Commander in Chief, Pacific, with intelligence on Japanese military capabilities and intentions—in other words, the information he needed to beat the Japanese into unconditional surrender.
The Iwo Jima Intelligence Operation
The JICPOA began collecting information on Iwo Jima after Nimitz authorized its seizure in August 1944 through Operation Detachment.2 He needed the island as an air base to support strategic bombing operations over Japan. Furthermore, Japanese fighters based on Iwo harassed bombers flying from the Marianas to Japan, a threat he had to neutralize.
JICPOA sources for the Iwo intelligence operation included aerial and submarine photographs, POW interrogations, intercepted communications, and captured documents from the 31st Army Headquarters on Saipan, which the Marines overran in June 1944. The documents included maps of the target island, navigational charts, and order-of-battle plans.
Many months prior to D-Day, units such as the U.S. Army's 7th Air Force, based on Saipan, flew more than 200 photoreconnaissance missions over Iwo Jima for the JICPOA. Unfortunately, directors of the operation focused most flights on the area immediately surrounding Airfield No. 1, likely because it bordered the landing beaches. Marine after-action reports stated that these photos were of no value in analyzing the whole of the island.3
Closer to D-day, P-38 Lightnings from the 28th Photographic Reconnaissance Squadron flew missions over Iwo Jima as low as 50 feet and produced the best photographic coverage of any campaign carried out under Nimitz. These contributed to a "Joint Enemy Installations Map" printed on 11 February 1945 and distributed to the ground element as it cycled through Guam and Saipan before cruising to the final objective.
Tragically, the JICPOA did not have seasoned intelligence analysts review the late photographs from the P-38 missions.4 Why? Because toward the end of January 1945, it lost all of its experienced photographic analysts to the Advanced Intelligence Center (AIC) just starting on Guam and to a U.S. Navy rotation policy that transferred officers in "administrative-type" occupational specialties to different locations or jobs at regular intervals. Those officers who had begun their intelligence careers at the JICPOA as photo interpreters simply had arrived at their time of transfer, so they left. In his report of intelligence activities at the end of the war, General Twitty said the incident, "left JICPOA for the moment without adequate experienced personnel" and "handicapped the work then in progress. . . ."5
Nevertheless, the JICPOA managed to publish its main Iwo Jima intelligence report on 10 January 1945. Weeks later, and as D-day neared, Marine intelligence followed with a last-minute update that revealed startling details on Iwo's defenses. It said that by 10 February 1945, the Japanese had increased their firepower and defensive fortifications by 100% in some cases. These increases, however, did not represent defense capabilities beyond the JICPOA's original estimates for Iwo Jima, so neither Nimitz nor his subordinates recommended altering the attack plan.
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.
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 Over all, 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.
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.
In its after-action report, the JICPOA stated that, "In attacking these positions no Japs were to be seen, all being in caves or crevices in the rocks and so dispersed as to give an all-round interlocking defense to each small compartment."20 The report bolstered its findings in an 11-photograph pictorial that dealt strictly with terrain.21
Incorrect assumptions about the Japanese plan of defense compounded order of battle and terrain difficulties. The JICPOA believed the Japanese planned to defend Iwo Jima with a thickly layered beach-oriented defense on the island's southern half. Pre-battle intelligence stated that "the heaviest concentration of infantry defenses on Iwo Jima is on the southern half of the island in the vicinity of Airfields No. 1 and No. 2 and the good beaches in that area."22 Analysts assumed the Japanese would focus their firepower directly on the Marines as they disembarked from their landing craft.23
Japanese defensive positions and troop allocation was not what was expected, however. Except those on Mount Suribachi, enemy defenses covered the northern half of the island in two wide belts that afforded intricately overlapping fields of fire. The Japanese called them fukkaku. A Marine after-action intelligence report stated that the area north of Airfield No. 1 was replete with concrete and steel fortifications and that the majority of these positions had not been picked up by photo intelligence.24 Mount Suribachi stood alone in the south, studded by infantry, mortars, machine guns, pillboxes, caves, and blockhouses. The Japanese also planned to use Suribachi as a fire-support base to cover the entire island, one of the few facets of Japanese defense the JICPOA's analysts recognized accurately.25
Regarding troop allocation, the Japanese deployed few soldiers at the southern end of the island where analysts expected the Japanese to make their primary defense. The heaviest concentrations of Japanese were in the north, and these troops fought to the death. The Japanese based their strategy on a simple concept: keep the Marines hung up on Iwo for as long as possible and kill as many as feasible in the process. The JICPOA's after-action intelligence concluded: "It was this simple tactic, coupled with the incredible rocky terrain and the maximum use the enemy had made of this terrain in constructing fortified positions which made the capture of Iwo Jima so difficult."
The JICPOA's faulty intelligence also had a negative impact on the preliminary naval bombardment. Because analysts had not discovered half of the enemy troop concentrations on the island, the shelling was not as effective as it should have been.
On D-3 and -2, battleships such as the Tennessee and Nevada bombarded beach areas while the New York fired in the vicinity of Airfield Nos. 1 and 2. Battleships used huge 14- and 12-inch guns. Smaller cruisers such as the Chester and Salt Lake City fired on the remaining sectors to the north, using lighter 8- and 6-inch guns.26 The same bombardment plan went off with little variation on D-1. As a result, the areas of sparse troop concentration received the heaviest bombardment, and vice-versa.
An after-action Navy gunfire report indicated that, although the bombardment accomplished its major task of providing enough fire support to allow the Marines to establish a beachhead, it was not effective enough to soften the target before the Marines landed, which ideally should have cut down on casualties and the length of the battle. It concluded by stating that the bombardment suffered for three reasons: not enough ships, not enough time, and not enough accurate intelligence.27
Conclusion
Why did these intelligence mistakes occur? In brief, the main reasons are:
Photo interpreters did not receive good coverage of the entire island until one month before the Marines landed. This meant two things: analysts did not have enough effective media to analyze early in the intelligence operation, and when they did receive it, they had less time to analyze it because of their dissemination deadline.
The loss of experienced photo interpreters in late January decreased the JICPOA's ability to analyze February photos that showed a dramatic increase in defensive installations on the objective. The loss also kept the center from helping Marine intelligence do its job. The Navy rotation policy that forced the incident was an incredible miscalculation.
Captured documents that foretold Japanese strength on Iwo had proved reliable for past operations, specifically, Guam, Tinian, and Peleliu. But although the Iwo Jima-related documents proved correct, they showed only part of the picture. Since intelligence analysts relied largely on the documents to estimate the size of Iwo Jima's garrison, their estimates were wrong. They did achieve source corroboration between the documents and photographs in three cases that dealt with Japanese weaponry, and such evidence must have compelled the JICPOA to believe it had better intelligence than it did.
Photographs of extensive layered trench lines and pillboxes just off Iwo's beaches reinforced JICPOA's belief that the Japanese would defend from the shoreline. They had used the beach defense, or a variant of it, in many successive campaigns, so a pattern existed. As of February 1945, the Japanese also were continuing to string 6,700 yards of wire and dig 42,100 yards of trenches along the eastern beaches.28 General Tadamichi Kuribayashi, the Japanese commander on Iwo Jima, purposely left the trenches in the open to deceive U.S. forces, and he ordered 135 pillboxes built on or near the beaches at the request of Navy officers under his command.29 They believed in the shore-based defense. The general did not. A Marine G-2 after-action report indicated that dummy positions along the island's beaches fooled U.S. forces into thinking that the Japanese would use a beach defense.
On Iwo Jima, the Japanese conducted the most effective counter-intelligence operation of any island yet attacked under Admiral Nimitz's command. Aside from brilliant deception operations, the Japanese had used camouflage to the maximum, and "most of the gun positions were totally hidden." This effective tactic hid hundreds of enemy positions from U.S. reconnaissance efforts.30
What lessons can be learned from the Iwo Jima campaign? Number one, an intelligence organization should be left alone to conduct its business. This is not to say it should have a blank check, but bureaucratic meddling from higher offices within or outside the intelligence community can impede and even halt the intelligence cycle.
Iwo Jima also points out that even the most convincing evidence can lead to the wrong conclusions, a tricky yet common hazard in the intelligence business. We missed the big picture. As a result, war planners and combatants paid for the intelligence deficit with time, resources, and casualties. But while the JICPOA indeed made mistakes in the Iwo Jima operation, up to that point it had served Nimitz well in scores of past campaigns. And even for Iwo Jima, it provided Nimitz with enough intelligence to win, thereby accomplishing a key objective of intelligence. The organization was a success, despite instances such as Iwo Jima. But even when it produced near-perfect intelligence, it could not curb the heavy impact of war; Marines, soldiers, and sailors still died, and mishaps on the battlefield still occurred. Accordingly, the intelligence lessons learned in the Pacific War, especially at Iwo Jima, have much to offer today's national security community.
1. Richard Wheeler, Iwo (New York: Lippincott & Crowell, Publishers, 1980) p. 234.
2. Whitman S. Bartley, Iwo Jima: Amphibious Epic (Washington, DC: Historical Branch, G-3 Division, Headquarters Marine Corps, 1954), pp. 19-21.
3. Headquarters, Expeditionary Troops, Task Force Fifty-Six, G-2 Report on Iwo Jima Operation, 1 April 1945, p. 1.
4. G-2 Report on Iwo Jima Operation, 1 April 1945, pp. 1-2.
5. Joseph J. Twitty, Report of Intelligence Activities in the Pacific Ocean Areas, "The Growth of JICPOA," Pearl Harbor, HI, 15 October 1945, p. 7.
6. JICPOA Information Bulletin 9-45, p. 2.
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.
8. JICPOA Information Bulletin 9-45, p. 1.
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)."
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.
11. Headquarters, Expeditionary Troops, Task Force Fifty-Six, State of Enemy Defenses, Iwo Jima, 13 February 1945, pp. 1-2.
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.
13. JICPOA Information Bulletin 9-45, 1, plus "Nearshore, Beach, and Soil Conditions, Iwo Jima" map that includes minute detail on Japanese defense installations.
14. Headquarters, Expeditionary Troops, Task Force Fifty-Six, State of Enemy Defenses, Iwo Jima, 13 February 1945, p. 2.
15. JICPOA Information Bulletin 136-45, Defense Installations on Iwo Jima (Pearl Harbor, HI: 10 June 1945,) p. 5.
16. JICPOA Information Bulletin 136-45, p. 4. The majority of Japanese concrete fortifications on Iwo were steel reinforced.
17. JICPOA Information Bulletin 136-45, p. 19.
18. JICPOA Information Bulletin 136-45, p. 2.
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).
20. JICPOA Information Bulletin 136-45, p. 4.
21. JICPOA Information Bulletin 136-45, pp. 11-16.
22. JICPOA Information Bulletin 9-45, p. 2.
23. JICPOA Information Bulletin 9-45, pp. 4-5.
24. Headquarters, Expeditionary Troops, Task Force Fifty-Six, G-2 Report on Iwo Jima Operation, p. 36.
25. JICPOA Information Bulletin 136-45, p. 3.
26. John Moore, ed., Jane's American Fighting Ships (New York: Mallard Press, 1991,) pp. 38-50, pp. 110-118.
27. Headquarters, V Amphibious Corps, Landing Force, Iwo Jima, Special Staff Section Reports, Appendix 2, "Report of Naval Gunfire Officer," pp. 21-22.
28. Headquarters, Expeditionary Troops, Task Force Fifty-Six, State of Enemy Defenses, Iwo Jima, p. 2.
29. Col. Joseph Alexander USMC (Ret.), Storm Landings: Epic Amphibious Battles of the Central Pacific (Annapolis, MD: Naval Institute Press, 1997) p. 132.
30. Headquarters, Expeditionary Troops, Task Force Fifty-Six, G-2 Report on Iwo Jima peration, 1 April 1945, pp. 35-36.