It is not widely known due to the limited scale of the action and its poor results, but three months after their devastating attack on Pearl Harbor, the Japanese carried out a second raid. The aim was to force the U.S. fleet to venture into open waters and engage in a decisive battle, taking advantage of its unfavorable conditions. This operation, named Operation K, did not go as planned and is remembered primarily as the first seaplane bombing raid and the one that covered the greatest distance.
As we know, the U.S. naval base at Pearl Harbor, located on the Hawaiian island of Oahu, was unexpectedly devastated on December 7, 1941, by several waves of hundreds of Japanese aircraft launched from six carriers. The intent was to strike at the U.S.‘s military might in the Pacific just before Japan’s invasion of Southeast Asia. That operation, designated as Operation Z by the Imperial General Headquarters, sank four battleships, damaged eight others, destroyed 188 planes, and killed nearly 2,500 people. However, it fell short of total success.
This was because four of the sunken ships were salvaged thanks to the harbor’s shallow depth, and critical components were recovered from others. Moreover, key island facilities such as the shipyard, power plant, fuel depots, workshops, docks, and headquarters remained intact. Most importantly, the major aircraft carriers (Lexington, Enterprise, Saratoga, Yorktown, and Hornet) were not present on the island, ensuring that the U.S. Navy’s power in the Pacific remained intact—a factor that would ultimately prove decisive in the Allied victory in the region.

Indeed, that Day of Infamy prompted President Roosevelt to immediately announce his country’s entry into World War II. Meanwhile, Japan was brimming with optimism and sought ways to extend its string of victories. Ten days after the attack, a reconnaissance plane was launched from the submarine I-7 to fly over Hawaii and assess the situation. The mission revealed that the Americans were repairing the damage at a brisk pace. Consequently, the Naval Department of the Imperial General Headquarters decided that it was necessary to hinder those efforts with a second, demoralizing blow.
This time, however, the approach had to differ, as it was impossible to gather the same force as before (six carriers, 414 aircraft, five cruisers, nine destroyers, and 23 submarines). These resources were needed to combat the Royal Navy in the imminent invasion of Hong Kong and Malaya, then British possessions. The solution emerged when this necessity coincided with a technical objective: testing the capabilities of the H8K flying boats. As their name suggests, these were canoe-type seaplanes built by the Kawanishi company, initially designed for maritime patrols.
Thanks to their four Mitsubishi MK4 engines, the H8K (referred to by the Americans as Emily) had a long operational range, and their size (a wingspan of 38 meters) allowed for substantial armament (five Type 92 machine guns and five Type 99 automatic cannons). They could also carry 2,000 kilograms of bombs or 64 soldiers; they could even transport two heavy torpedoes mounted under their wings. Other advantages included the robust fuselage armor and onboard fire suppression systems, making them difficult to shoot down. However, initial tests on December 31, 1941, revealed poor water performance.
After making the necessary adjustments to their keel, the revised designs passed new tests in early 1942, receiving the Navy’s approval. The flying boats were then assigned a pivotal role in the much-debated second raid on Pearl Harbor. The plan initially involved five aircraft that were to gather at the French Frigate Shoals, the largest atoll northwest of the Hawaiian archipelago. This posed a logistical challenge: the operation required a full moon for visibility over the targets and calm seas to refuel from submarines.

As on December 7, U.S. codebreakers uncovered the plan and its intended location, but inexplicably, their warnings were ignored by commanders. This may have been due to the involvement of Lieutenant Jasper Holmes, who, under the pseudonym Alec Hudson, had published a story titled “Rendezvous” in the Saturday Evening Post the previous August. This fictional tale described U.S. planes refueling from submarines at a remote island to carry out a long-distance air raid.
Once again, the Japanese were set to operate unimpeded over Oahu, which remained the principal theater of war in the early stages of the conflict. Initially, the raid was intended to target California or Texas, but circumstances redirected the mission to Hawaii. When the time came, only two seaplanes were available, piloted by Lieutenant Hisao Hashizume, who was given command of the mission, and Ensign Shosuke Sasao. Despite this, the Chief of Staff of the 24th Air Squadron traveled to Tokyo, met with the Military Command and the Combined Fleet, and decided to proceed with the operation.
While one submarine was dispatched to monitor Hawaii, two others, equipped with torpedo tubes modified for refueling hoses, reached the French Frigate Shoals. In the first week of March, the two seaplanes landed there after traveling from the Wotje Atoll in the Marshall Islands, over 3,000 kilometers away. Each aircraft carried four 250-kg bombs. After refueling as planned, they resumed their journey at 4:00 p.m. on March 4. Operation K was underway.
There were no shortages of setbacks. The mission was initially scheduled for February but had to be postponed for a couple of days due to the U.S. Navy’s attempt to recapture Wake Island (an atoll halfway between Hawaii and the Marianas), lost on December 24 (the future president George Bush participated in the bombings). Likewise, the submarine I-23, tasked with positioning itself south of Pearl Harbor to report on weather conditions and recover the crews of downed seaplanes, disappeared on February 14, never to be heard from again.

Therefore, Hashizume and Sasao would have to carry out their mission relying on the skies over French Frigate Shoals being clear. Although Japanese cryptologists had deciphered the enemy’s code and could predict the weather, the Americans changed it on March 1. The Americans also made mistakes. The Kauai station detected the aircraft approaching at 6:44 p.m. and dispatched a Curtiss P-40 Warhawk fighter and a PBY Catalina (Consolidated Model 28) seaplane to intercept them. However, dense cloud cover prevented their location, as the planes were flying above it at 15,000 feet.
What was advantageous in one respect turned out to be detrimental in another: the clouds also confused the Japanese. Hashizume took Kaena Point’s lighthouse as a reference and turned north of the island, while Sasao turned south, failing to receive his instructions. The first part of the mission—observing the recovery efforts at Pearl Harbor—was impossible due to the lack of visibility, so they focused on the second part: hindering those efforts by bombing a dock known as Ten-Ten because of its length of 1,010 feet (nearly 308 meters).
However, this too posed significant challenges. The cloud cover allowed Hashizume only intermittent glimpses of land, worsened by the island’s lights being turned off due to Kauai’s warning, while anti-aircraft searchlights were switched on instead. He had to drop the bombs blindly, and the four explosives fell on the slopes of Mount Tantalus, an ash cone of an extinct volcano overlooking the northern part of Honolulu, the only area with electrical wiring—though, as mentioned, it had been disconnected at the time for safety.
The bombs caused no damage, as the nearest structure, President Theodore Roosevelt High School, was 300 meters away. The only effects were craters between six and nine meters wide and three meters deep, along with a few broken window panes due to the shockwave. Since there were only two attacking planes and they were not sighted, the Americans couldn’t provide a coherent explanation for the explosions, with the Army and Navy blaming each other for causing them.

The fact that there were no human casualties was another factor in letting the matter slide, even though the Japanese media claimed to have echoed a radio news report from Los Angeles that spoke of about thirty dead and seventy injured, including both military personnel and civilians. This, despite the fact that Ensign Sasao’s intervention was even more futile: unable to see anything on land—considering it was already past nine at night and raining—he decided to drop his bombs over the sea, without it being clear whether it was off Waianae or Pearl Harbor, going completely unnoticed.
Upon their withdrawal, the two aircraft set course southwest toward the Marshall Islands. Sasao landed at Wotje Atoll, the point from which they had departed the previous day, but Hashizume had sustained hull damage while taking off from French Frigate Shoals and feared that base lacked the resources for necessary repairs, so he decided to continue flying to Jaluit Atoll, also in the same archipelago but farther away. Thus, he completed what was the longest unescorted bombing mission in history up to that time.
It was estimated that his H8K would need a few days in the workshop, which, combined with adverse weather and the lack of moonlight, forced the suspension of the operation for the rest of the month, awaiting the next full moon. However, on March 10, with the seaplane ready and having taken off toward Midway for a new mission, it was detected by an American radar and shot down by Brewster F2A Buffalo fighters that intercepted it. And so, even though it seemed to mark the end of Operation K, there was still an epilogue.
That name was retained for the observation tasks initiated over the Hawaiian area of influence in preparation for the next step in Japan’s Pacific expansion: Operation MI. Admiral Yamamoto thus designated the conquest of the Midway Islands, a major U.S. naval air base in the Pacific that had to be neutralized to prevent it from facilitating a repeat of the Doolittle Raid, an incursion against Tokyo, Yokosuka, and Nagoya carried out by Lieutenant Colonel James H. Doolittle on April 18 as a response to the attack on Pearl Harbor.

Although the American planes took off from the USS Hornet, the archipelago itself could be considered a massive natural aircraft carrier that, logically, the Americans would protect at all costs, deploying the cream of their fleet, including carriers. And that was exactly what the Japanese expected, doing the same with hopes of destroying the enemy in a single blow, compensating for the semi-failure of Pearl Harbor and avoiding a new bombing of the islands, which they deemed too risky.
It should be noted that, according to their reports, the U.S. only had two carriers left, the Hornet and the Enterprise, as the Lexington had sunk and the Yorktown was also believed to be lost by the Japanese (in reality, it had been severely damaged but managed to reach Pearl Harbor) during the first week of May in the Battle of the Coral Sea. They assumed both carriers were based in Hawaii, but this needed verification. Therefore, while the Aleutian Islands were invaded as a diversion, two seaplanes were deployed to fly toward the archipelago again.
Their mission was to verify the presence of the carriers and confirm the reports provided by deployed submarines, ensuring all data was available before June 3, as the force destined to capture Midway was to depart from Saipan on May 28. However, the mission, scheduled for May 30, had to be canceled because U.S. analysts had deciphered enemy codes, and Admiral Chester Nimitz sent two ships to French Frigate Shoals to mine its waters, preventing any seaplane landings there.
The Japanese submarine I-123 spotted the ships and raised the alarm. As an alternative for the necessary refueling, Necker Island, an uninhabited rocky mass that is the remnant of a volcanic cone located 120 kilometers from the atoll and less than 700 kilometers northwest of Honolulu, was proposed. However, the idea was ultimately not approved, and Operation K was definitively canceled. The Imperial Japanese Navy would have to face the Battle of Midway blindly, although at the time it felt invincible and did not assign much importance to this; a grave mistake, because, among other things, the U.S. had repaired the Yorktown in just 24 hours, giving them an aerial numerical superiority that led to their victory.
This article was first published on our Spanish Edition on December 18, 2024: Operación K, el fallido segundo bombardeo japonés de Pearl Harbor con hidroaviones tres meses después del primer ataque
SOURCES
Sue Bradford Edwards, The bombing of Pearl Harbor
Keith Warren Lloyd, Avenging Pearl Harbor. The Saga of America’s Battleships in the Pacific War
William Cole, Date lives on in few memories
Larry Dwyer, Kawanishi H8K “Emily”
Michael Coffey, Días de infamia. Grandes errores militares de la Segunda Guerra Mundial
Wikipedia, Operación K
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