The Kawanishi H8K Emily: the flying boat the Allies rated hardest to shoot down

What makes the H8K Emily special

Kawanishi H8K2 Emily: full specifications

Baseline note: the figures below describe the H8K2, Navy Type 2 Large Flying Boat Model 12 — the Kasei 22-engined mark that entered service in 1943, of which 112 were built and which flew the great majority of the type’s wartime sorties. Deltas for the 13-Shi prototypes, the Kasei 12-engined H8K1 Model 11, the experimental H8K3 and H8K4 and the H8K2-L Seikū transport are in grey. Metric values follow the Kawanishi and Kaigun Koku Hombu tables as reprinted by René Francillon and in Japanese compilations; where the standard Western lists round or convert differently — and on wingspan and fuel capacity they plainly do — both readings are named.

Armament & payload

The H8K carried five 20 mm cannon, two torpedoes and enough fuel for a day in the air, and was the only Japanese aeroplane Allied crews genuinely did not want to attack

Every other big flying boat of the war was defended by rifle-calibre machine guns and hope. The H8K2 was defended by five 20 mm cannon — bow turret, dorsal turret, tail turret and one in each beam blister — backed by five 7.7 mm guns in hull hatches, so that there was no approach to it that did not run into a cannon. That was a genuinely formidable arrangement in 1943, and it was mounted on an aeroplane fast enough that a fighter had to work to get into a firing position at all.

What made it lethal rather than merely well armed was the protection behind the guns. Japanese aircraft of the period were built light and burned readily; the H8K was built with partially self-sealing hull tanks over fuel-proof bilges, a carbon-dioxide inerting system and armour at the crew stations. Allied fighter pilots who had learned that a burst into a Betty or a Mavis produced a fire found that the same burst into an Emily produced holes. The type acquired a reputation across the Pacific as the hardest Japanese aircraft to bring down, and René Francillon’s judgement — "the most outstanding water-based combat aircraft of the Second World War" — is not really contested.

Offensively it was a torpedo and bomb carrier as well as a scout: two torpedoes or 2,000 kg of bombs and depth charges on racks between the engine nacelles. Its very first operational sortie was a bombing mission, and one of the strangest of the war. On the night of 4 March 1942 two H8K1s of the Yokohama Kōkūtai flew Operation K — the second raid on Pearl Harbor. They staged 3,060 km (1,900 miles) from Wotje in the Marshalls to French Frigate Shoals, an uninhabited reef 900 km (560 miles) north-west of Oahu, refuelled on the water from submarines waiting there, and pressed on to Hawaii with four 250 kg (550 lb) bombs apiece. Gun and store fits varied widely: H8K1s carried a lighter battery, some late H8K2s had the beam blisters deleted in favour of sliding hatches, and the transport marks kept only a bow cannon and a single rearward-firing gun.

Sourcing caveat: Japanese ordnance nomenclature and Western reporting names do not map cleanly, and gun fits were changed in the field. The five-cannon battery is the standard H8K2 fit and is well attested from the captured aircraft and from Allied gun-camera and intelligence reports, but individual airframes carried more or fewer 7.7 mm guns, and the blister positions were deleted on some late aircraft. Ordnance weights follow the Japanese loading tables, which round.

Variants

Kawanishi built 167 H8Ks in five years, fixed the prototype’s hull before anyone else saw it, and exactly one airframe still exists

The Imperial Japanese Navy issued the 13-Shi Large Flying Boat requirement in 1938, when the H6K "Mavis" it was meant to replace had barely entered service. The demand was extraordinary: a cruising range beyond 7,400 km, a speed of well over 400 km/h, two torpedoes, and heavy defensive armament — in other words, an aeroplane thirty per cent better than the H6K in every dimension at once. Dr Shizuo Kikuhara’s team at Kawanishi answered with a deep, fine-lined hull of high length-to-beam ratio and a long shoulder-mounted wing, and got the aerodynamics almost exactly right.

They got the hydrodynamics badly wrong. The prototype was completed on 31 December 1940 and flew in January 1941 — not, as is often written, in 1940 — and its behaviour on the water was frightening. The fine hull that gave such low air drag threw enormous sheets of spray into the propellers and porpoised violently on the step, to the point that the aircraft was barely controllable during take-off and landing. The fix was unglamorous and complete: the hull was made about 0.50 m (1 ft 8 in) deeper, the planing bottom was reshaped, and spray strips were added under the nose. Two further pre-production aircraft followed in December 1941, and the type was cleared for production. It is worth noticing how rare this was in wartime Japanese practice — a fundamental defect found, admitted and properly engineered out before the aeroplane reached a squadron.

What emerged was the best flying boat of the war by a clear margin, and the Navy never had enough of them. Production ran at six or seven a month at Kawanishi’s Konan and Naruo plants near Kobe, against thousands of Catalinas; 167 aircraft of all marks were completed. They flew reconnaissance, anti-shipping and night bombing from Rabaul, the Marshalls, the Kuriles, Singapore and the home islands, and after 1943 increasingly at night, because Allied fighter cover had made daylight patrol lethal even for an aeroplane this tough. They also carried the Navy’s senior officers: on 31 March 1944 two H8K2s flying Admiral Mineichi Koga and his chief of staff Vice Admiral Shigeru Fukudome from Palau to Davao ran into a typhoon. Koga’s aircraft was lost with all aboard, Fukudome’s ditched off Cebu, and the copy of the Combined Fleet’s "Z Plan" he carried passed through Filipino guerrillas into American hands — one of the most consequential aircraft accidents of the war.

13-Shi Experimental / H8K1 (1940–41, 5 aircraft)

Prototype completed 31 December 1940, first flight January 1941, plus four development machines. Kasei 12 engines. Poor water handling led to the deeper hull, reshaped planing bottom and nose spray strips that defined every later aircraft.

H8K1, Navy Type 2 Large Flying Boat Model 11 (1941–42, 12 built)

First service mark. Four 1,530 hp Kasei 12, lighter gun fit, about 433 km/h. Flew Operation K in March 1942 and the earliest Pacific patrols. Some references count these as 14 or 16 by folding in development airframes.

H8K1-L, Type 2 Transport Flying Boat (November 1943, 1 conversion)

The surviving prototype rebuilt as a 41-passenger transport with dorsal turret and beam blisters removed and augmented exhausts fitted. A one-off, and the proof of concept for the Seikū.

H8K2, Model 12 (1943–45, 112 built)

The definitive aircraft and the baseline of the specification above. Kasei 22 with water-methanol injection, 467 km/h, greater fuel capacity, an improved tail turret and the full five-cannon battery. Late batches carried Type 3 Ku Mark 6 ASV radar; some had the beam blisters replaced by sliding hatches.

H8K2-L Seikū ("Clear Sky"), Model 32 (1943–45, 36 built)

Dedicated transport built at the Naruo plant. Dorsal turret, blisters and ventral hatch deleted, hull tanks removed to free volume, leaving one 20 mm in the bow and one 13 mm firing aft. Carried 29 staff passengers or up to 64 troops; range fell to about 2,200 km. This is the mark that flew the Navy’s senior officers around the shrinking empire.

H8K3, Model 22 (1944, 2 built)

Drag-reduction experiment: retractable wingtip floats, retractable dorsal turret, sliding hatch gun positions instead of blisters, and Fowler flaps. Works numbers 596 and 597. Faster, but too late and too complicated to matter.

H8K4, Model 23 (1945, 2 conversions)

The two H8K3s re-engined with 1,825 hp Kasei 25b. No production; by 1945 Japanese industry was building fighters for home defence and nothing else.

H8K4-L Seikū, Model 33 (1945, project only)

Transport version of the H8K4, abandoned when flying boat production was stopped in favour of interceptors.

G9K Gunzan (project only, no aircraft built)

Proposed land-based attack bomber derivative of the H8K airframe. It existed on paper; the "G9K" designation is a post-war retrospective convention rather than a wartime allocation.

Survivors: exactly one original H8K exists anywhere in the world, and there are no reproductions. It is H8K2 manufacture number 426, built at Kawanishi’s Konan plant at Kobe and completed in March 1943; it served with the 802nd Kōkūtai as N1-26, with the 801st on Saipan as 801-86 from April 1944, and finally with the Takuma Kōkūtai at Takuma seaplane base on Shikoku as T-31, where it surrendered in early September 1945. Japanese mechanics made it airworthy for the Americans and it was ferried to Yokohama; it reached Naval Air Station Norfolk, Virginia in 1946, though accounts differ on the route — one has it shipped aboard the escort carrier USS Anzio departing on 18 January 1946, another crated to Whidbey Island and thence through the Panama Canal. It was rebuilt at Norfolk without manuals, blueprints or spares by 23 May 1946, made a single American flight from Hampton Roads to NAS Patuxent River with Commander Thomas F. Connolly at the controls — losing two engines en route and a third after landing — underwent hydrodynamic testing, and then sat at Chambers Field for thirty-three years. Hurricane Donna tore it from its moorings in September 1960 and flipped it onto its starboard side, wrecking the number four engine. It was displayed at Gate 4 in the 1970s, then stored, and was scheduled for disposal in 1976. Congress approved its transfer to the Museum of Maritime Science in Tokyo on 23 April 1979 at the urging of the museum’s president, Ryoichi Sasakawa; it was craned onto a barge on 31 May and reached Japan on 13 July 1979, and after restoration was unveiled on 21 July 1980 as an outdoor exhibit on the Tokyo waterfront. In late January 2004 it moved again, to the JMSDF Kanoya Air Base Museum at Kanoya in Kagoshima Prefecture, where it is now displayed under cover in a sealed, air-conditioned environment, the first indoor home it has had since it left Takuma in 1945. Two H8K wrecks are also known: one in shallow water off the west coast of Saipan, confusingly nicknamed the "B-29" by local divers, and one in Chuuk Lagoon off the south-western end of Dublon Island.

The H8K Emily: from ocean patrol to museum survivor

The Emily up close: twelve stories

The H8K Emily in pictures

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The H8K Emily in motion

A verified, high-authority video feature on the Kawanishi H8K is coming soon. In the meantime, explore the gallery above and the stories of the aircraft’s design, protection and long-range operations.

Where the H8K Emily flew

The record that defines the H8K Emily

The Emily’s record is written less in air-to-air kills than in reach, endurance and survivability. It flew long ocean patrols, scouted for fleets, hunted submarines and carried out bombing and torpedo strikes across the Pacific — and it earned an Allied reputation as the hardest Japanese aircraft to shoot down. Its most famous single operation, the submarine-refuelled Operation K raid on Pearl Harbor, achieved nothing militarily but demonstrated an extraordinary range.

Compare the combat record of every military aircraft. Figures as of 2026.

Everything people ask about the Kawanishi H8K Emily

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Every fact, checked

• The National WWII Museum — The Second Pearl Harbor Attack, 1942Authoritative museum account of Operation K, the submarine-refuelled second raid.
• HistoryOfWar.org — Kawanishi H8K “Emily”Development history, protection features, per-variant production and H8K2 specifications.
• Military Factory — Kawanishi H8K (Emily)Full specification sheet, variant list and production totals.
• Pacific Wrecks — H8K2 Emily No. 426 (Tail T-31)Complete provenance of the sole survivor, from wartime service to Kanoya display.
• Pearl Harbor Historic Sites — Operation KNarrative of the raid and its link to French Frigate Shoals and Midway.
• Smithsonian National Air and Space Museum — H8K referenceInstitutional reference on the type and its preservation.
• WW2DB — H8K specificationCross-check reference for dimensions, weights and performance figures.
• We Are The Mighty — Operation KDistances, bomb impacts and the record-range framing of the raid.