What was Operation K, carried out by Japanese armed forces in World War II?

Operation K involved sending Kawanishi H8K "Emily" flying boats (pictured) to reconnoitre the damage done to Pearl Harbor and to disrupt repair and salvage operations.

Although the plan involved several of the large flying boats, in the end just two were available. In March 1942 they took off from the Marshall Islands, met a Japanese submarine for refuelling in the French Frigate Shoals, and proceeded to fly to Hawaii. The raid was largely a failure as they were unable to locate Oahu because of the blackout. The raid was planned for a moonlit night, but they misread the US coded weather reports and picked a cloudy evening. One aircraft dropped its bombs in error over the ocean before heading back out to sea. The other crashed into Hawaii’s Tantalus Peak volcano just north of Honolulu, in the darkness, alerting the Americans to what was going on.

From the Japanese standpoint the raid was a failure. But they planned to do it again in June. For the Americans it was an intelligence windfall. It allowed them to work out how the H8Ks got to Hawaii. The June flight was to be Admiral Yamamoto’s bid to determine if the American aircraft carriers were in port at Pearl Harbor just before the Midway attacks. The pilots had to abort the mission when their refuelling submarine discovered French Frigate Shoals to be occupied by an American destroyer and minesweeper. This prevented Yamamoto from knowing that the American carriers were already at sea laying a trap at Midway.