Japanese seaplanes and the second bombing of Pearl Harbor

The combatants of World War II had skilled designers who delivered aircraft to meet each nation’s needs. In pre-war Japan, the vast oceanic expanses of the Pacific inspired seaplane designs.

The Kawanishi company received a contract from the Japanese Navy in mid-1938 to create a new flying boat specifically intended to best the British Short Sunderland and American Sikorsky XPBS-1 in performance.

A traditional-looking four-engine high-wing design ensued, but when the prototype Kawanishi H8K1 first tested its wings in January 1941, water-handling was poor, with sea spray tossed into the engines and even over the wing.

A deepening of the hull, accompanied by alterations in the planing surfaces that contacted the water, and the addition of longitudinal steps to the boat hull, made the H8K feasible.

Mitsubishi radial engines providing 1,530 horsepower were later supplanted by engines of 1,850 horsepower on the H8K2 variant of the patrol bomber, which was given the code name “Emily” by the Allies.

The H8K2’s more powerful engines gave it a top speed boost of more than 20 miles an hour over the H8K1 above 16,000 feet, and the more powerful H8K2 could top out at 290 mph.

Maximum range exceeded 4,400 miles on the operational H8K2. The original specification called for the bomber to achieve a maximum patrol range of 5,180 statute miles, but operational aircraft tend to exhibit a weight gain that diminishes some of the intended performance markers.

Flexible machine gun mounts and turrets for 20-millimeter cannons made the H8K a formidable foe. Yet photos survive showing U.S. Navy PB4Y-1 Liberator patrol bombers attacking, and downing, the Kawanishis with .50-caliber machine gunfire.

Since patrol bombers of both nations were the long-range eyes in the sky, it was not unusual for these patrol planes to encounter each other far from home.

Underwing carriage of torpedoes, bombs, or depth charges made the H8K1 and H8K2 lethal sub and shipping hunters. But their debut as land bombers the night of March 4, 1942, proved inauspicious when cloud cover obscured the prized target of Honolulu. The largely unheralded second attack by the Japanese on Oahu was a bust.

Even the long-ranging H8K1s needed a gas stop en route from the Marshall Islands to reach Hawaii, and a Japanese submarine lingered in French Frigate Shoals to provide fuel.

From its service debut in early 1942, the H8K Emily served front line Japanese Navy units up through VE Day in 1945. Just as U.S. Navy PB2Y Coronado four-engine flying boat bombers were converted to transports during the war, the H8K design lent itself to 36 units built as transports.

A total of 167 of all versions of the H8K were built — a small tally by World War II standards. But as the war turned increasingly defensive for the Japanese armed forces, in later years emphasis was placed on fighter, not seaplane, construction.

By war’s end, at least four intact Kawanishi H8K Emily flying boats were tallied.

One H8K2 was taken to the U.S., where the Navy evaluated it at Patuxent River, Maryland.

A 1947 article in Naval Aviation News suggested the Emily was a good airplane, but only a middlin’ seaplane.

Years later, aviation historian Rene Francillon wrote a different epitaph for the Kawanishi H8K, calling it “the most outstanding water-based combat aircraft of the Second World War” in his book, “Japanese Aircraft of the Pacific War.”

The captured Emily remained in the U.S. as a war trophy for decades until the sole surviving H8K was returned to Japan in 1979 for display.