Operation K, the Second Attack on Pearl Harbor Kept Secret for Decades


The Japanese attack on Pearl Harbor on December 7, 1941, which forced the United States into World War II, is well known and has been the subject of many books and movies. It occurred with little advance warning and resulted in huge U.S. losses in terms of hardware and personnel.

What is less well known is that the Japanese planned and executed a less successful follow-up operation intended to thwart the American salvage operations at Pearl Harbor, as well as further disrupt the U.S. Navy’s Pacific Fleet.

Operation Kē-Sakusen was planned for the night of March 4, 1942 and was supposed to be conducted by five massive long-range Kawanishi H8K flying boats. However, due to operational issues, by the time the planned date for the attack arrived there were only two flying boats available for the mission.

Japanese Attack on Pearl Harbor

The H8Ks were originally earmarked for mainland bombing campaigns, including targets in California and Texas, but first the Japanese military planners needed to know how repairs were going in Hawaii.

The H8Ks were perfect for reconnaissance and, as they were also each able to deliver a payload of four 550-pound bombs, they could further disrupt the Pacific Fleet as a bonus.

The first strike on Pearl Harbor had been seen as a tremendous success by the Imperial Japanese Navy, but subsequent Japanese reconnaissance missions had confirmed that the U.S. Navy’s salvage efforts were progressing at a rapid pace.

U.S. maritime warning systems had been strengthened since the first attack on Pearl Harbor, so approaching Hawaii by sea was impossible.

Photograph of Battleship Row taken from a Japanese plane at the beginning of the attack. The explosion in the center is a torpedo strike on USS West Virginia. Two attacking Japanese planes can be seen: one over USS Neosho and one over the Naval Yard.

Therefore, the Japanese military pinned its hopes on their long-range bombers. The primary target was the 1010 dry dock, since hitting the ships that were undergoing repairs would delay the U.S. Pacific Fleet’s recovery and improve the odds for the Japanese fleet.
It was a historic raid in that it was the longest distance ever undertaken during a two-plane bombing mission, and it was one of the longest bombing sorties conducted without fighter planes as escorts.

Ships docked at Ten-Ten Dock.

The flight from the Marshall Islands to Pearl Harbor and back covered more than 2,000 miles. In order to make the mission viable, two submarines were dispatched to the tiny atolls of French Frigate Shoals with tanks of aviation fuel, so that the flying boats could refuel before the final 500-mile approach.

The date was set to coincide with a full moon in order to provide maximum visibility for the reconnaissance part of the operation. In the days before the mission, U.S. intelligence observers noted the deployment of the bombers and alerted the Naval authorities at Ohau, but the warnings were largely ignored.

Battle of Midway. U.S. Douglas SBD-3 Dauntless dive bombers of VS-8 from USS Hornet about to attack the burning Japanese cruiser Mikuma for the third time on 6 June 1942.

Lieutenant Hisao Hashizume was the Japanese mission commander and flew the first H8K. Ensign Shosuke Hisao piloted the second. As the mission got underway, thick clouds came up, providing a shield for the aircraft–but also hindering visibility for the crews on board.

The H8Ks were supposed to attack in tandem, but the men in the second aircraft couldn’t hear the orders coming from the lead plane. The planes split up, and their bombs were dropped without proper targeting.

H8K1 supplementary prototype number 2 taking off in February 1942.

The first plane’s bombs fell on a mountainside near a school in Honolulu. There were no casualties, and just a few windows were broken. The second plane’s bombs fell into the Pacific Ocean. The flying boats returned to the Marshall Islands, where they landed at separate air bases.

Read another story from us: Niihau Incident at Pearl Harbor – Local Hawaiians Fought Downed Japanese Pilot and Sympathizers

The only real outcome of Operation Kē-Sakusen was that the U.S. found out that the Imperial Japanese forces could still penetrate its airspace and leave without being intercepted.

The U.S. Army and Navy then blamed each other for the nighttime explosions in Honolulu as part of a military cover-up that lasted for decades.

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