Three months after Pearl Harbor, two enormous Japanese flying boats lifted off from a lagoon in the Marshall Islands and set course for Hawaii. Their plan was almost absurd: fly nearly 2,000 miles across empty ocean, meet a submarine at a deserted reef to refuel, and bomb Pearl Harbor a second time. The aircraft that could even attempt such a thing was the Kawanishi H8K — the machine the Allies code-named "Emily," and which many historians still call the finest flying boat of the war.

The raid failed. The aircraft did not. And the story of both is the story of a warplane so good that Allied crews came to regard it as the hardest thing in the Pacific sky to shoot down.

A flying boat that could fight back

Most flying boats of the era were lumbering, lightly armed patrol craft — easy prey once a fighter found them. The Emily was different. Kawanishi wrapped four powerful engines and a deep, clean hull around a surprising amount of muscle: as many as five 20 mm cannon in nose, tail, dorsal and beam positions, backed by machine guns, armour plate, partially self-sealing fuel tanks and even a carbon-dioxide fire-suppression system.

The result was a maritime patrol bomber that could shrug off hits and shoot back hard while still ranging thousands of miles. It could carry bombs, depth charges or torpedoes, scout vast stretches of the Pacific, and defend itself well enough that intercepting one was genuinely dangerous.

A full history of the H8K and why it earned its reputation for toughness.

Operation K: the raid that almost repeated Pearl Harbor

On the night of March 4, 1942, two H8Ks set out to prove the type's range in the most audacious way imaginable. The plan, code-named Operation K, sent them from Wotje Atoll toward Oahu, with a refuelling rendezvous by submarine at the lonely French Frigate Shoals roughly halfway there. It was reconnaissance and harassment rolled into one — and a demonstration that Hawaii was still within reach.

Then the weather intervened. Heavy cloud smothered Oahu, and the crews bombed blind. Their loads fell harmlessly — on a hillside above Honolulu and into the sea — doing no meaningful damage. But the sheer distance the flying boats covered, refuelling from a submarine at a barren reef in the dark, remains one of the boldest long-range missions of the entire war.

Rare wartime footage of the Emily, 1944.

The one that survived

For all its quality, the Emily could not turn the tide; only 167 were built as Japan's industry buckled. Allied fighters and radar eventually made even the toughest patrol boat vulnerable. Yet the reputation held.

One H8K still exists, preserved in Japan — the sole survivor of a design that outclassed every Western flying boat it met. The second Pearl Harbor raid is a footnote; the aircraft that flew it is not.

A closer look at the Imperial Japanese Navy's finest flying boat.

Sources: Rene J. Francillon, Japanese Aircraft of the Pacific War; Wikipedia (Kawanishi H8K, Operation K); Pacific Eagles.