|Part of the Pacific Theater of World War II|
Approximate route of Operation K.
|United States||Empire of Japan|
|Commanders and leaders|
|none||2 Kawanishi H8Ks
|Casualties and losses|
|minimal private property damage||none|
Operation K (K作戦 Kē-Sakusen ) was a Japanese naval operation in World War II, intended as a reconnaissance of Pearl Harbor and disruption of repair and salvage operations following the surprise attack on December 7, 1941. It culminated on March 4, 1942, with an unsuccessful attack carried out by two Kawanishi H8K "Emily" flying boats. This was the longest distance ever undertaken by a two-plane bombing mission, and the longest bombing sortie ever planned without fighter escort.
The planning for Operation K began in the weeks after the attack on Pearl Harbor, when the Imperial Japanese Navy high command considered how to take advantage of the capabilities of the long-range H8K flying boats. Plans to bomb California and Texas were being discussed, when the need for updated information regarding the repairs to US Navy facilities at Pearl Harbor took precedence. An assessment of the repairs to the docks, yards and airfields of O'ahu would help the IJN staff to determine American ability to project power for months to come.
Initial plans called for the use of five H8K aircraft. They would fly to Kānemilohaʻi (also known as the French Frigate Shoals), the largest atoll in the Northwestern Hawaiian Islands, to be refueled by submarines prior to taking off for O'ahu. If the first raid was successful, additional raids would be made.
In a repeat of events just prior to the December 7 attack, American codebreakers warned that the Japanese were preparing for reconnaissance and disruption raids, refueling at Kānemilohaʻi, and again were largely ignored by their superiors.
When time came for the raid, only two of the big flying boats were available. Pilot Lieutenant Hisao Hashizume was in command of the mission, with Ensign Shosuke Sasao flying the second airplane. They were sent to Wotje Atoll in the Marshall Islands, where each airplane was loaded with four 550-pound (250 kg) bombs. From there, they flew 1,900 miles (3,100 km) to French Frigate Shoals to refuel, then set off for O'ahu, 560 miles (900 km) distant. In addition to their reconnaissance mission, they were to bomb the "Ten-Ten" dock - named for its length, 1,010 feet (310 m) - at the Pearl Harbor naval base to disrupt salvage and repair efforts. However, a comedy of errors ensued on both sides.
American radar stations on Kaua'i (and later O'ahu) picked up and tracked the two planes as they approached the main Hawaiian Islands, prompting a search by P-40 Warhawk fighters. PBY Catalina flying boats were also sent to seek Japanese aircraft carriers, which were assumed to have launched the two invaders. However, heavy clouds (and possibly an overcast below the H8Ks) prevented the defenders from spotting the Japanese planes, which were flying at an altitude of 15,000 feet (4,600 m).
Those same clouds also confused the IJN pilots. Using the Ka'ena Point lighthouse for a position fix, Hashizume decided to attack from the north. Sasao, however, did not hear Hashizume's order and instead turned to skirt the southern coast of Oahu.
Hashizume, having lost sight of his wingman, and only able to see small patches of the island, dropped his four bombs on the slopes of Tantalus Peak, an extinct volcano cinder cone just north of Honolulu sometime between 2-2:15am HST. He was unable to see Pearl Harbor, the only lit facility on Oahu due to blackout conditions intended to hinder air raids. Hashizume's bombs landed about 1,000 feet (300 m) from Roosevelt High School, creating craters 6–10 feet (1.8-3 m) deep and 20–30 feet (6.1-9.1 m) across. Damage was limited to shattered windows. Sasao is assumed by historians and officials to have eventually dropped his bombs into the ocean, either off the coast of Wai'anae or near the sea approach to Pearl Harbor. The two flying boats then flew southeast toward the Marshall Islands. Sasao returned as planned to Wotje atoll, but Hashizume's airplane had sustained hull damage while taking off from French Frigate Schoals. Fearing the primitive base at Wotje was insufficient to repair the damage, Hashizume proceeded non-stop all the way to their home base at Jaluit Atoll, also in the Marshall Islands. That made his flight the longest bombing mission in history up to that point.
There were no American casualties. The raid did raise new fears of a potential Japanese invasion of Hawaii.
Japanese media repeated an unsubstantiated Los Angeles radio report of "considerable damage to Pearl Harbor" with 30 dead sailors and civilians, with 70 wounded. Both the U.S. Army and U.S. Navy blamed each other for the explosions, accusing each other of jettisoning munitions into Tantalus.
Another armed reconnaissance mission, scheduled for March 6, or 7, was canceled because of the delay in launching the first raid, damage to Hashizume's airplane, and the aircrews' exhaustion. It was carried out on 10 March 1942, but Hashizume was killed when his flying boat was shot down by Brewster F2A Buffalo fighters near Midway Atoll.
A followup to Operation K was scheduled for May 30, to gain intelligence on the whereabouts of U.S. carriers prior to the Battle of Midway. However the Americans had become aware French Frigate Shoals were a possible IJN rendezvous point, and naval patrols were increased, per Admiral Chester Nimitz's orders. A Japanese submarine spotted two American warships at anchor there, prompting a cancellation of the plan. This left IJN unable to observe U.S. Navy activity, or to keep track of the American aircraft carriers.
The raid did affect U.S. Navy morale. Nimitz's chief of intelligence, Captain Edwin T. Layton, whimsically suggested one of Commander Rochefort's men, Wilfrid J. "Jasper" Holmes, had planned the attack, since it closely followed a story he had written for the Saturday Evening Post before the war, "Rendezvous". Holmes was exonerated.
See also 
- Budnick, Rich (2005). Hawaii's Forgotten History: the good...the bad...the embarrassing. Aloha Press. ISBN 0-944081-04-5.
- Horn, Steve (2005). The Second Attack on Pearl Harbor: Operation K and Other Japanese Attempts to Bomb America in World War II. Naval Institute Press. ISBN 1-59114-388-8.
- Simpson, MacKinnon (2008). Hawaii Homefront: Life in the Islands during World War II. Bess Press. ISBN 978-1-57306-281-7.