Operation K: The Second Raid on Pearl Harbor

Everyone of course knows about the Japanese attack on Pearl Harbor in December 1941. But not many people have ever heard of the second Japanese air raid on Pearl Harbor, which took place just a few months later.

H8K Emily flying boat

In the aftermath of the December 7, 1941, attack, the Japanese were watching the progress of the American efforts to repair the damage, using Yokusuka “Glen” floatplanes launched from submarines to overfly the islands. Surprised by how rapidly the US Navy was repairing the damaged battleships and port facilities, the Japanese Navy made plans for another air raid on Hawaii, to disrupt the repair operations and also perhaps to hit an American carrier in port.

By this time, the focus of the fighting had moved to the western Pacific, especially the area around Australia and New Guinea. The Imperial Japanese Navy could not spare any aircraft carriers for another voyage to Hawaii, and in any case the Americans had beefed up their warning systems, making a surprise approach by sea impossible. So the Japanese decided to launch their air raid without any carriers.

The weapon they chose was the Kawanishi H8K1 flying boat, an immense seaplane, known as “Emily” to the Allies, that could take off and land on water. The four-engined Emily had a wingspan of 124 feet, and was heavily armed with ten machine guns and ten 20mm cannon. It was used mostly for coastal patrol, antisubmarine duty and reconnaissance. But the seaplane could also carry two torpedos or four 500kg bombs. The Japanese Navy had just begun deploying the Emily in early February: the seaplanes had not yet flown any combat missions.

The closest place to Hawaii from which the Emilys could operate was at Wotje in the Marshall Islands, about 2,000 miles away from Pearl Harbor. Although the Emily carried enough fuel for a full 24 hours of flight, this was too far to go in one round trip. So the planners would dispatch two Japanese submarines, fitted with special fuel tanks to carry aviation gas, to the tiny French Frigate Shoals, about five hundred miles northwest of Hawaii. The Emilys, loaded with bombs, would take off from Wotje, fly to the French Frigate Shoals and land in the lagoon to be refuled from the submarines, then take off for Pearl Harbor. Since the trip was too far for any Japanese fighter, they would be flying without escort. To make it more difficult for American defenses, therefore, it was planned that the Emilys would arrive over their destination in the middle of the night. The primary target was the Ten Ten Dock, the 1,010-foot drydock that was used to service and repair the American battleships and carriers. Putting the dock out of action would delay the US recovery from the December air raid, and would also complicate repairs to any American carrier that happened to be damaged in operations around New Guinea. The plan became known as Operation K.

In February 1942, Japanese radio nets crackled with messages back and forth as the mission was planned out and the pieces moved into place. A group of Emily flying boats were sent to Wotje, and the submarines I-17 and I-19 were sent to the French Frigate Shoals. But unknown to the Japanese, they were not the only ones listening. The US Navy’s cryptologic team had successfully broken the Japanese Navy’s codes, and they were able to decrypt enough to figure out that an operation was being planned against Pearl Harbor for early March. The intelligence warning was passed on to Navy officials. When the Emilys took off on March 4, the Americans didn’t know the details, but they knew something was about to happen.

The Japanese, meanwhile, had already run into difficulties. Originally, five Emilys were to take part in the raid, but in the end only two were available–a drastic reduction in the potential effectiveness of the attack. The submarine I-23 had been dispatched to a location just south of Oahu to give weather reports, but sometime in the weeks before the bombers took off, the submarine disappeared (it is still not known what happened to it). So when the Emilys set out for Pearl Harbor after their submarine refueling, they did not know what weather they would encounter there.

In the time since the December 7 attack, Pearl Harbor’s defenses had been strengthened. There were routine patrols by sea and air, and a ring of radar installations now circled Oahu, operated by newly-trained members of the Women’s Air Raid Defense (WARD). Shortly before 2am on the morning of March 5, WARD operators picked up a set of signals on their radar screens indicating two unidentified aircraft approaching from the northwest. This warning was forwarded to the office of the Commander-in-Chief Pacific (CINCPAC). Assuming that the two targets were advance scouts for a Japanese naval force that was attempting to carry out another carrier raid on Oahu, the Navy quickly dispatched four P-40 Warhawk fighters to intercept them, and also sent five American PBY Catalina flying boats to search the area for the “enemy fleet”. But the art of radar-directed night-fighting was still in its infancy, and the P-40’s were unable to find the incoming bogies in the dark. The Emilys were able to make their approach to Pearl Harbor unmolested.

But the darkness and the unexpected cloudy weather was causing problems for the Emilys as well. The two Japanese planes got separated in the darkness and ended up approaching from two different directions. And although they had achieved complete surprise and faced no American opposition, they were unable to see their target and were both forced to aim more or less by guess. One of the Emilys dropped its bombs harmlessly into the ocean, the other hit a high school building about six miles away.

Although the military effects of Operation K had been nil, the raid had psychological effects both in the US and Japan. The Americans were shocked that enemy airplanes, just three months after the Pearl Harbor raid, had once again been able to overfly the base and escape unharmed. Press reports in Hawaiian newspapers mistakenly reported damage to the harbor and 100 American casualties: Japanese spies passed these inaccuracies on to the Imperial Navy, who were elated by their apparent success.

Indeed, the Japanese were so happy with the their attack that they decided to try again, and began laying plans for a repeat of the operation to be set for May 30. This was to be a reconnaissance mission to help locate the American carriers in advance of the planned campaign at Midway, and also an attempt to damage any carrier that happened to be in port and take it out of the upcoming battle.

But once again, decoded intercepts told the US that something was up–and by now the Americans had figured out that the Japanese Emilys had used the French Frigate Shoals for refueling and dispatched two Navy ships to anchor in the lagoon. When the Japanese tanker-submarine I-121 arrived a few days before the new mission was to be launched, it saw American ships there waiting for it, and withdrew. The operation was cancelled.

3 thoughts on “Operation K: The Second Raid on Pearl Harbor”

  1. Somewhat off on a tangent:
    During the battle of the Atlantic, one of the major problems faced by the Allies was that they couldn’t have air cover for the convoys all the way. It recently occurred to me that in principle, they could have used float planes for such operations. The planes could simply land at sea and refuel from ships in the convoy.

    Or perhaps it wouldn’t be so simple. I don’t know whether such a plan was ever considered. Reading a book about the U-boat nightmare in the Atlantic at the moment; perhaps it will tell. 😉

  2. They eventually solved the convoy problem by building small “escort carriers” that could accompany the convoy and provide air cover all the time.

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