The H8K entered production in 1941 and first saw operational use on the night of 4 March 1942 in a second raid on Pearl Harbourr. Since the target lay out of range for the flying boats, this audacious plan involved a refuelling by submarine at French Frigate Shoals, some 550 miles north-west of Hawaii, en route. Two planes from the Yokohama Kokutai(Naval Air Corps) attempted to bomb Pearl Harbor, but, due to poor visibility, did not accomplish any significant damage.

Six days after the second Pearl harbor raid one of the Emilys was sent on a daylight photo-recon mission of Midway Atoll. It was intercepted by radar directed Brewster Buffalo fighters of Marine Corps squadron VMF-221 and shot down. All aboard were killed including Lt. Hashizume Hisao, the lead pilot of the second Pearl Harbor raid.

H8K2s were used on a wide range of patrol, reconnaissance, bombing, and transport missions throughout the Pacific war. The H8K2 was given the Allied code name "Emily".

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