Attack on Pearl Harbor
The attack on Pearl Harbor, also known as the Battle of Pearl Harbor, the Hawaii Operation or Operation AI by the Japanese Imperial General Headquarters, and Operation Z during planning, was a surprise military strike by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii Territory, on the morning of December 7, 1941. The attack led to the United States' entry into World War II.
Japan intended the attack as a preventive action to keep the U.S. Pacific Fleet from interfering with military actions the Empire of Japan planned in Southeast Asia against overseas territories of the United Kingdom, the Netherlands, and the United States. Over the next seven hours there were coordinated Japanese attacks on the U.S.-held Philippines, Guam and Wake Island and on the British Empire in Malaya, Singapore, and Hong Kong.
The attack commenced at 7:48 a.m. Hawaiian Time. The base was attacked by 353 Imperial Japanese fighter planes, bombers, and torpedo planes in two waves, launched from six aircraft carriers. All eight U.S. Navy battleships were damaged, with four sunk. All but the USS Arizona (BB-39) were later raised, and six were returned to service and went on to fight in the war. The Japanese also sank or damaged three cruisers, three destroyers, an anti-aircraft training ship,[nb 4] and one minelayer. 188 U.S. aircraft were destroyed; 2,403 Americans were killed and 1,178 others were wounded. Important base installations such as the power station, shipyard, maintenance, and fuel and torpedo storage facilities, as well as the submarine piers and headquarters building (also home of the intelligence section) were not attacked. Japanese losses were light: 29 aircraft and five midget submarines lost, and 64 servicemen killed. One Japanese sailor, Kazuo Sakamaki, was captured.
The attack came as a profound shock to the American people and led directly to the American entry into World War II in both the Pacific and European theaters. The following day, December 8, the United States declared war on Japan. Domestic support for non-interventionism, which had been fading since the Fall of France in 1940, disappeared. Clandestine support of the United Kingdom (e.g., the Neutrality Patrol) was replaced by active alliance. Subsequent operations by the U.S. prompted Nazi Germany and Fascist Italy to declare war on the U.S. on December 11, which was reciprocated by the U.S. the same day.
From the 1950s, several writers alleged that parties high in the U.S. and British governments knew of the attack in advance and may have let it happen (or even encouraged it) with the aim of bringing the U.S. into war. However, this advance-knowledge conspiracy theory is rejected by mainstream historians.[nb 5]
There were numerous historical precedents for unannounced military action by Japan. However, the lack of any formal warning, particularly while negotiations were still apparently ongoing, led President Franklin D. Roosevelt to proclaim December 7, 1941, "a date which will live in infamy". Because the attack happened without a declaration of war and without explicit warning, the attack on Pearl Harbor was judged by the Tokyo Trials to be a war crime.
War between Japan and the United States had been a possibility of which each nation had been aware (and developed contingency plans for) since the 1920s, though tensions did not begin to grow seriously until Japan's 1931 invasion of Manchuria. Over the next decade, Japan continued to expand into China, leading to all-out war between those countries in 1937. Japan spent considerable effort trying to isolate China and achieve sufficient resource independence to attain victory on the mainland; the "Southern Operation" was designed to assist these efforts.
From December 1937, events such as the Japanese attack on USS Panay, the Allison incident, and the Nanking Massacre (the International Military Tribunal of the Far East concluded that more than 200,000 Chinese non-combatants were killed in indiscriminate massacres, though other estimates have ranged from 40,000 to more than 300,000) swung public opinion in the West sharply against Japan. Fearing Japanese expansion, the United States, the United Kingdom, and France provided loan assistance for war supply contracts to the Republic of China.
In 1940, Japan invaded French Indochina in an effort to control supplies reaching China. The United States halted shipments of airplanes, parts, machine tools, and aviation gasoline to Japan, which was perceived by Japan as an unfriendly act.[nb 6] The U.S. did not stop oil exports to Japan at that time in part because prevailing sentiment in Washington was that such an action would be an extreme step that Japan would likely consider a provocation, given Japanese dependence on U.S. oil.
Early in 1941, President Franklin D. Roosevelt moved the Pacific Fleet to Hawaii from its previous base in San Diego and ordered a military buildup in the Philippines in the hope of discouraging Japanese aggression in the Far East. Because the Japanese high command was (mistakenly) certain that any attack on the UK's Southeast Asian colonies would bring the U.S. into war, a devastating preventive strike appeared to be the only way to avoid U.S. naval interference. An invasion of the Philippines was also considered necessary by Japanese war planners. The U.S. War Plan Orange had envisioned defending the Philippines with a 40,000-man elite force. This was opposed by Douglas MacArthur, who felt that he would need a force ten times that size, and was never implemented. By 1941, U.S. planners anticipated abandonment of the Philippines at the outbreak of war and orders to that effect were given in late 1941 to Admiral Thomas Hart, commander of the Asiatic Fleet.
The U.S. ceased oil exports to Japan in July 1941, following Japanese expansion into French Indochina after the fall of France, in part because of new American restrictions on domestic oil consumption. This in turn caused the Japanese to proceed with plans to take the Dutch East Indies, an oil-rich territory.[nb 7] On August 17, Roosevelt warned Japan that the U.S. was prepared to take steps against Japan if it attacked "neighboring countries". The Japanese were faced with the option of either withdrawing from China and losing face or seizing and securing new sources of raw materials in the resource-rich, European-controlled colonies of Southeast Asia.
Japan and the U.S. engaged in negotiations during the course of 1941 in an effort to improve relations. During these negotiations, Japan offered to withdraw from most of China and Indochina when peace was made with the Nationalist government, adopt an independent interpretation of the Tripartite Pact, and not to discriminate in trade provided all other countries reciprocated. Washington rejected these proposals. Japanese Prime Minister Konoye then offered to personally meet with Roosevelt, but Roosevelt insisted on coming to an agreement before any meeting. The U.S. ambassador to Japan repeatedly urged Roosevelt to accept the meeting, warning that it was the only way to preserve the conciliatory Konoye government and peace in the Pacific. His recommendation was not acted upon. The Konoye government collapsed the following month when the Japanese military refused to agree to the withdrawal of all troops from China.
Japan's final proposal, on November 20, offered to withdraw their forces from southern Indochina and not to launch any attacks in Southeast Asia provided that the U.S., the UK, and the Netherlands ceased aiding China and lifted their sanctions against Japan. The American counter-proposal of November 26 (November 27 in Japan) (the Hull note) required Japan to evacuate all of China without conditions and conclude non-aggression pacts with Pacific powers. However the day before the Hull Note was delivered, on November 26 in Japan, the main Japanese attack fleet left port for Pearl Harbor.
Preliminary planning for an attack on Pearl Harbor to protect the move into the "Southern Resource Area" (the Japanese term for the Dutch East Indies and Southeast Asia generally) had begun very early in 1941 under the auspices of Admiral Isoroku Yamamoto, then commanding Japan's Combined Fleet. He won assent to formal planning and training for an attack from the Imperial Japanese Navy General Staff only after much contention with Naval Headquarters, including a threat to resign his command. Full-scale planning was underway by early spring 1941, primarily by Rear Admiral Ryunosuke Kusaka, with assistance from Captain Minoru Genda and Yamamoto's Deputy Chief of Staff, Captain Kameto Kuroshima. The planners studied the 1940 British air attack on the Italian fleet at Taranto intensively.[nb 8][nb 9]
Over the next several months, pilots trained, equipment was adapted, and intelligence collected. Despite these preparations, Emperor Hirohito did not approve the attack plan until November 5, after the third of four Imperial Conferences called to consider the matter. Final authorization was not given by the emperor until December 1, after a majority of Japanese leaders advised him the "Hull Note" would "destroy the fruits of the China incident, endanger Manchukuo and undermine Japanese control of Korea."
By late 1941, many observers believed that hostilities between the U.S. and Japan were imminent. A Gallup poll just before the attack on Pearl Harbor found that 52% of Americans expected war with Japan, 27% did not, and 21% had no opinion. While U.S. Pacific bases and facilities had been placed on alert on many occasions, U.S. officials doubted Pearl Harbor would be the first target; instead, they expected the Philippines would be attacked first. This presumption was due to the threat that the air bases throughout the country and the naval base at Manila posed to sea lanes, as well as to the shipment of supplies to Japan from territory to the south. They also incorrectly believed that Japan was not capable of mounting more than one major naval operation at a time.
Ever since the Japanese attack, there has been debate as to how and why the United States had been caught unaware, and how much and when American officials knew of Japanese plans and related topics. Military officers including Gen. Billy Mitchell had pointed out the vulnerability of Pearl to air attack. At least two Naval War games, one in 1932 and another in 1936 proved that Pearl was vulnerable to such an attack. Adm. James Richardson was removed from command shortly after protesting President Roosevelt's decision to move the bulk of the Pacific fleet to Pearl Harbor. The decisions of military and political leadership to ignore these warnings has contributed to conspiracy theories. Several writers, including journalist Robert Stinnett and former United States rear admiral Robert Alfred Theobald, have argued that various parties high in the U.S. and British governments knew of the attack in advance and may even have let it happen or encouraged it in order to force the U.S. into war via the so-called "back door". However, this Pearl Harbor advance-knowledge conspiracy theory is rejected by mainstream historians.
The Japanese attack had several major aims. First, it intended to destroy important American fleet units, thereby preventing the Pacific Fleet from interfering with Japanese conquest of the Dutch East Indies and Malaya and to enable Japan to conquer Southeast Asia without interference. Second, it was hoped to buy time for Japan to consolidate its position and increase its naval strength before shipbuilding authorized by the 1940 Vinson-Walsh Act erased any chance of victory. Third, to deliver a blow to America's ability to mobilize its forces in the Pacific, battleships were chosen as the main targets, since they were the prestige ships of any navy at the time. Finally, it was hoped that the attack would undermine American morale such that the U.S. government would drop its demands contrary to Japanese interests, and would seek a compromise peace with Japan.
Striking the Pacific Fleet at anchor in Pearl Harbor carried two distinct disadvantages: the targeted ships would be in very shallow water, so it would be relatively easy to salvage and possibly repair them; and most of the crews would survive the attack, since many would be on shore leave or would be rescued from the harbor. A further important disadvantage—this of timing, and known to the Japanese—was the absence from Pearl Harbor of all three of the U.S. Pacific Fleet's aircraft carriers (Enterprise, Lexington, and Saratoga). IJN top command was so imbued with Admiral Mahan's "decisive battle" doctrine—especially that of destroying the maximum number of battleships—that, despite these concerns, Yamamoto decided to press ahead.[page needed]
Japanese confidence in their ability to achieve a short, victorious war also meant other targets in the harbor, especially the navy yard, oil tank farms, and submarine base, were ignored, since—by their thinking—the war would be over before the influence of these facilities would be felt.
Approach and attack
On November 26, 1941, a Japanese task force (the Striking Force) of six aircraft carriers—Akagi, Kaga, Sōryū, Hiryū, Shōkaku, and Zuikaku—departed northern Japan en route to a position northwest of Hawaii, intending to launch its 408 aircraft to attack Pearl Harbor: 360 for the two attack waves and 48 on defensive combat air patrol (CAP), including nine fighters from the first wave.
The first wave was to be the primary attack, while the second wave was to attack carriers as its first objective and cruisers as its second, with battleships as the third target. The first wave carried most of the weapons to attack capital ships, mainly specially adapted Type 91 aerial torpedoes which were designed with an anti-roll mechanism and a rudder extension that let them operate in shallow water. The aircrews were ordered to select the highest value targets (battleships and aircraft carriers) or, if these were not present, any other high value ships (cruisers and destroyers). First wave dive bombers were to attack ground targets. Fighters were ordered to strafe and destroy as many parked aircraft as possible to ensure they did not get into the air to intercept the bombers, especially in the first wave. When the fighters' fuel got low they were to refuel at the aircraft carriers and return to combat. Fighters were to serve CAP duties where needed, especially over U.S. airfields.
Before the attack commenced, two reconnaissance aircraft launched from cruisers Chikuma and Tone were sent to scout over Oahu and Maui and report on U.S. fleet composition and location. Reconnaissance aircraft flights risked alerting the U.S., and were not necessary. U.S. fleet composition and preparedness information in Pearl Harbor was already known due to the reports of the Japanese spy Takeo Yoshikawa. A report of the absence of the U.S. fleet in Lahaina anchorage off Maui was received from the fleet submarine I-72. Another four scout planes patrolled the area between the Japanese carrier force (the Kido Butai) and Niihau, to detect any counterattack.
Fleet submarines I-16, I-18, I-20, I-22, and I-24 each embarked a Type A midget submarine for transport to the waters off Oahu. The five I-boats left Kure Naval District on November 25, 1941. On December 6, they came to within 10 nautical miles (19 km; 12 mi) of the mouth of Pearl Harbor and launched their midget subs at about 01:00[clarification needed] on December 7. At 03:42 Hawaiian Time, the minesweeper Condor spotted a midget submarine periscope southwest of the Pearl Harbor entrance buoy and alerted the destroyer Ward. The midget may have entered Pearl Harbor. However, Ward sank another midget submarine at 06:37[nb 10] in the first American shots in the Pacific Theater. A midget submarine on the north side of Ford Island missed the seaplane tender Curtiss with her first torpedo and missed the attacking destroyer Monaghan with her other one before being sunk by Monaghan at 08:43.
A third midget submarine, Ha-19, grounded twice, once outside the harbor entrance and again on the east side of Oahu, where it was captured on December 8. Ensign Kazuo Sakamaki swam ashore and was captured by Hawaii National Guard Corporal David Akui, becoming the first Japanese prisoner of war.[nb 11] A fourth had been damaged by a depth charge attack and was abandoned by its crew before it could fire its torpedoes. Japanese forces received a radio message from a midget submarine at 00:41 on December 8 claiming damage to one or more large warships inside Pearl Harbor.
In 1992, 2000, and 2001, Hawaii Undersea Research Laboratory's submersibles found the wreck of the fifth midget submarine lying in three parts outside Pearl Harbor. The wreck was in the debris field where much surplus U.S. equipment was dumped after the war, including vehicles and landing craft. Both of its torpedoes were missing. This correlates with reports of two torpedoes fired at the light cruiser St. Louis at 10:04 at the entrance of Pearl Harbor, and a possible torpedo fired at destroyer Helm at 08:21.
Japanese declaration of war
See also: Japanese war crimes
The attack took place before any formal declaration of war was made by Japan, but this was not Admiral Yamamoto's intention. He originally stipulated that the attack should not commence until thirty minutes after Japan had informed the United States that peace negotiations were at an end. However, the attack began before the notice could be delivered. Tokyo transmitted the 5000-word notification (commonly called the "14-Part Message") in two blocks to the Japanese Embassy in Washington, but transcribing the message took too long for the Japanese ambassador to deliver it in time. (In fact, U.S. code breakers had already deciphered and translated most of the message hours before he was scheduled to deliver it.) The final part of the "14 Part Message" is sometimes described as a declaration of war. While it was viewed by a number of senior U.S government and military officials as a very strong indicator that negotiations were likely to be terminated and that war might break out at any moment, it neither declared war nor severed diplomatic relations. A declaration of war was printed on the front page of Japan's newspapers in the evening edition of December 8, but not delivered to the U.S. government until the day after the attack.
For decades, conventional wisdom held that Japan attacked without any official warning of a break in relations only because of accidents and bumbling that delayed the delivery of a document hinting at war to Washington. In 1999, however, Takeo Iguchi, a professor of law and international relations at International Christian University in Tokyo, discovered documents that pointed to a vigorous debate inside the government over how, and indeed whether, to notify Washington of Japan's intention to break off negotiations and start a war, including a December 7 entry in the war diary saying, "our deceptive diplomacy is steadily proceeding toward success." Of this, Iguchi said, "The diary shows that the army and navy did not want to give any proper declaration of war, or indeed prior notice even of the termination of negotiations ... and they clearly prevailed."
First wave composition
The first attack wave of 183 planes was launched north of Oahu, led by Commander Mitsuo Fuchida. Six planes failed to launch due to technical difficulties. It included:[nb 12]
- 1st Group (targets: battleships and aircraft carriers)
- 2nd Group – (targets: Ford Island and Wheeler Field)
- 3rd Group – (targets: aircraft at Ford Island, Hickam Field, Wheeler Field, Barber's Point, Kaneohe)
As the first wave approached Oahu, it was detected by the U.S. Army SCR-270 radar at Opana Point near the island's northern tip. This post had been in training mode for months, but was not yet operational. The operators, Privates George Elliot Jr. and Joseph Lockard, reported a target. But Lieutenant Kermit A. Tyler, a newly assigned officer at the thinly manned Intercept Center, presumed it was the scheduled arrival of six B-17 bombers from California. The Japanese planes were approaching from a direction very close (only a few degrees difference) to the bombers, and while the operators had never seen a formation as large on radar, they neglected to tell Tyler of its size. Tyler, for security reasons, could not tell the operators of the six B-17s that were due (even though it was widely known).
As the first wave planes approached Oahu, they encountered and shot down several U.S. aircraft. At least one of these radioed a somewhat incoherent warning. Other warnings from ships off the harbor entrance were still being processed or awaiting confirmation when the attacking planes began bombing and strafing. Nevertheless, it is not clear any warnings would have had much effect even if they had been interpreted correctly and much more promptly. The results the Japanese achieved in the Philippines were essentially the same as at Pearl Harbor, though MacArthur had almost nine hours warning that the Japanese had already attacked Pearl Harbor.
The air portion of the attack began at 7:48 a.m. Hawaiian Time (3:18 a.m. December 8 Japanese Standard Time, as kept by ships of the Kido Butai),[nb 13] with the attack on Kaneohe. A total of 353 Japanese planes in two waves reached Oahu. Slow, vulnerable torpedo bombers led the first wave, exploiting the first moments of surprise to attack the most important ships present (the battleships), while dive bombers attacked U.S. air bases across Oahu, starting with Hickam Field, the largest, and Wheeler Field, the main U.S. Army Air Forces fighter base. The 171 planes in the second wave attacked the Army Air Forces' Bellows Field near Kaneohe on the windward side of the island, and Ford Island. The only aerial opposition came from a handful of P-36 Hawks, P-40 Warhawks, and some SBD Dauntless dive bombers from the carrier Enterprise.[nb 14]
In the first wave attack, about eight of the forty-nine 800 kg (1760 lb) armor-piercing bombs dropped hit their intended battleship targets. At least two of those bombs broke up on impact, another detonated before penetrating an unarmored deck, and one was a dud. Thirteen of the forty torpedoes hit battleships, and four torpedoes hit other ships. Men aboard U.S. ships awoke to the sounds of alarms, bombs exploding, and gunfire, prompting bleary-eyed men to dress as they ran to General Quarters stations. (The famous message, "Air raid Pearl Harbor. This is not drill.",[nb 15] was sent from the headquarters of Patrol Wing Two, the first senior Hawaiian command to respond.) The defenders were very unprepared. Ammunition lockers were locked, aircraft parked wingtip to wingtip in the open to prevent sabotage, guns unmanned (none of the Navy's 5"/38s, only a quarter of its machine guns, and only four of 31 Army batteries got in action). Despite this low alert status, many American military personnel responded effectively during the attack.[nb 16] Ensign Joe Taussig Jr., aboard Nevada, commanded the ship's antiaircraft guns and was severely wounded, but continued to be on post. Lt. Commander F. J. Thomas commanded Nevada in the captain's absence and got her under way until the ship was grounded at 9:10 a.m. One of the destroyers, Aylwin, got underway with only four officers aboard, all ensigns, none with more than a year's sea duty; she operated at sea for 36 hours before her commanding officer managed to get back aboard. Captain Mervyn Bennion, commanding West Virginia, led his men until he was cut down by fragments from a bomb which hit Tennessee, moored alongside.
Second wave composition
The second planned wave consisted of 171 planes: 54 B5Ns, 81 D3As, and 36 A6Ms, commanded by Lieutenant-Commander Shigekazu Shimazaki. Four planes failed to launch because of technical difficulties. This wave and its targets comprised:
- 1st Group – 54 B5Ns armed with 550 lb (249 kg) and 132 lb (60 kg) general-purpose bombs
- 27 B5Ns – aircraft and hangars on Kaneohe, Ford Island, and Barbers Point
- 27 B5Ns – hangars and aircraft on Hickam Field
- 2nd Group (targets: aircraft carriers and cruisers)
- 78 D3As armed with 550 lb (249 kg) general-purpose bombs, in four sections (3 aborted)
- 3rd Group – (targets: aircraft at Ford Island, Hickam Field, Wheeler Field, Barber's Point, Kaneohe)
- 35 A6Ms for defense and strafing (1 aborted)
The second wave was divided into three groups. One was tasked to attack Kāneʻohe, the rest Pearl Harbor proper. The separate sections arrived at the attack point almost simultaneously from several directions.
American casualties and damages
Ninety minutes after it began, the attack was over. 2,008 sailors were killed and 710 others wounded; 218 soldiers and airmen (who were part of the Army until the independent U.S. Air Force was formed in 1947) were killed and 364 wounded; 109 marines were killed and 69 wounded; and 68 civilians were killed and 35 wounded. In total, 2,403 Americans died and 1,178 were wounded. Eighteen ships were sunk or run aground, including five battleships. All of the Americans killed or wounded during the attack were non-combatants, given the fact there was no state of war when the attack occurred.
Of the American fatalities, nearly half were due to the explosion of Arizona's forward magazine after it was hit by a modified 40-centimetre (16 in) shell.[nb 17]
Already damaged by a torpedo and on fire amidships, Nevada attempted to exit the harbor. She was targeted by many Japanese bombers as she got under way and sustained more hits from 250 lb (113 kg) bombs, which started further fires. She was deliberately beached to avoid blocking the harbor entrance.
California was hit by two bombs and two torpedoes. The crew might have kept her afloat, but were ordered to abandon ship just as they were raising power for the pumps. Burning oil from Arizona and West Virginia drifted down on her, and probably made the situation look worse than it was. The disarmed target ship Utah was holed twice by torpedoes. West Virginia was hit by seven torpedoes, the seventh tearing away her rudder. Oklahoma was hit by four torpedoes, the last two above her belt armor, which caused her to capsize. Maryland was hit by two of the converted 40 cm shells, but neither caused serious damage.
Although the Japanese concentrated on battleships (the largest vessels present), they did not ignore other targets. The light cruiser Helena was torpedoed, and the concussion from the blast capsized the neighboring minelayer Oglala. Two destroyers in dry dock, Cassin and Downes were destroyed when bombs penetrated their fuel bunkers. The leaking fuel caught fire; flooding the dry dock in an effort to fight fire made the burning oil rise, and both were burned out. Cassin slipped from her keel blocks and rolled against Downes. The light cruiser Raleigh was holed by a torpedo. The light cruiser Honolulu was damaged, but remained in service. The repair vessel Vestal, moored alongside Arizona, was heavily damaged and beached. The seaplane tender Curtiss was also damaged. The destroyer Shaw was badly damaged when two bombs penetrated her forward magazine.
Of the 402 American aircraft in Hawaii, 188 were destroyed and 159 damaged, 155 of them on the ground. Almost none were actually ready to take off to defend the base. Eight Army Air Forces pilots managed to get airborne during the attack and six were credited with downing at least one Japanese aircraft during the attack: 1st Lt. Lewis M. Sanders, 2nd Lt. Philip M. Rasmussen, 2nd Lt. Kenneth M. Taylor, 2nd Lt. George S. Welch, 2nd Lt. Harry W. Brown, and 2nd Lt. Gordon H. Sterling Jr. Sterling was shot down by Lt. Fujita over Kaneohe Bay and is listed as Body Not Recovered (not Missing In Action). Lt. John L. Dains was killed by friendly fire returning from a victory over Kaawa. Of 33 PBYs in Hawaii, 24 were destroyed, and six others damaged beyond repair. (The three on patrol returned undamaged.) Friendly fire brought down some U.S. planes on top of that, including five from an inbound flight from Enterprise. Japanese attacks on barracks killed additional personnel.
At the time of the attack, nine civilian aircraft were flying in the vicinity of Pearl Harbor. Of these, three were shot down.
Fifty-five Japanese airmen and nine submariners were killed in the attack, and one was captured. Of Japan's 414 available planes, 29 were lost during the battle (nine in the first attack wave, 20 in the second),[nb 18] with another 74 damaged by antiaircraft fire from the ground.
Possible third wave
Several Japanese junior officers including Fuchida and Genda urged Nagumo to carry out a third strike in order to destroy as much of Pearl Harbor's fuel and torpedo[nb 19] storage, maintenance, and dry dock facilities as possible. Genda, who had unsuccessfully advocated for invading Hawaii after the air attack, believed that without an invasion multiple strikes were necessary to disable the base as much as possible. The captains of the other five carriers in the task force reported they were willing and ready to carry out a third strike. Military historians have suggested the destruction of these shore facilities would have hampered the U.S. Pacific Fleet far more seriously than the loss of its battleships. If they had been wiped out, "serious [American] operations in the Pacific would have been postponed for more than a year"; according to Admiral Chester Nimitz, later Commander in Chief of the Pacific Fleet, "it would have prolonged the war another two years." Nagumo, however, decided to withdraw for several reasons:
- American anti-aircraft performance had improved considerably during the second strike, and two thirds of Japan's losses were incurred during the second wave. Nagumo felt if he launched a third strike, he would be risking three quarters of the Combined Fleet's strength to wipe out the remaining targets (which included the facilities) while suffering higher aircraft losses.
- The location of the American carriers remained unknown. In addition, the admiral was concerned his force was now within range of American land-based bombers. Nagumo was uncertain whether the U.S. had enough surviving planes remaining on Hawaii to launch an attack against his carriers.
- A third wave would have required substantial preparation and turnaround time, and would have meant returning planes would have had to land at night. At the time, only the (British) Royal Navy had developed night carrier techniques, so this was a substantial risk.
- The task force's fuel situation did not permit him to remain in waters north of Pearl Harbor much longer, since he was at the very limit of logistical support. To do so risked running unacceptably low on fuel, perhaps even having to abandon destroyers en route home.
- He believed the second strike had essentially satisfied the main objective of his mission—the neutralization of the Pacific Fleet—and did not wish to risk further losses. Moreover, it was Japanese Navy practice to prefer the conservation of strength over the total destruction of the enemy.
At a conference aboard Yamato the following morning, Yamamoto initially supported Nagumo. In retrospect, sparing the vital dockyards, maintenance shops, and oil depots meant the U.S. could respond relatively quickly to Japanese activities in the Pacific. Yamamoto later regretted Nagumo's decision to withdraw and categorically stated it had been a great mistake not to order a third strike.