From the air, the patch of green on Akutan Island looked perfect: flat, grassy, a gift for a pilot with a dying engine. Petty Officer Tadayoshi Koga lowered his wheels and set up to land. The grass was hiding water. The moment his main gear touched, it dug into the bog, the fighter pitched over onto its back, and the 19-year-old was killed instantly.

Su Mitsubishi A6M Zero barely suffered. And that is what made the crash of 4 June 1942 one of the most consequential of the Pacific War. Five weeks later, a US Navy patrol crew found the wreck. By September it was flying in American markings over San Diego, and US test pilots were learning, one flight at a time, exactly where the most feared fighter in the Pacific was weak.

The Raid on Dutch Harbor

In early June 1942 the Imperial Japanese Navy was running two operations at once. The main effort was Midway. Far to the north, a smaller force including the light carrier Ryujo struck the US base at Dutch Harbor in the Aleutian Islands on 3 and 4 June. Koga flew in a section of three Zeros with Chief Petty Officer Makoto Endo and Petty Officer Tsuguo Shikada.

Over Dutch Harbor, Koga's fighter was hit. Investigators later found .50-calibre bullet holes and smaller holes, from above and below. One of them had severed the return oil line, and the Zero began trailing oil. Koga throttled back to keep the engine from seizing and headed for Akutan Island, 25 miles to the east.

Koga never got the chance to learn what went wrong with his landing. His aircraft stayed where it fell, upside down in the marsh, invisible to anyone who did not fly directly over it.

The Smithsonian Channel on how the captured Zero helped US pilots develop new tactics. Video: Smithsonian Channel

Found by a Lost Catalina

On 10 July 1942 a PBY Catalina flown by Lieutenant William "Bill" Thies was navigating by dead reckoning in the usual Aleutian murk when Machinist's Mate Albert Knack spotted wreckage below. It was a Zero, on its back, almost intact.

Thies led a team back to the site on 11 and 12 July. A second party under Lieutenant Robert Kirmse got the aircraft out on 15 July. Koga was buried near the crash site. The Zero went south on the transport USS St. Mihiel, reached Seattle on 1 August and continued by barge to Naval Air Station North Island in San Diego.

Mechanics at North Island straightened the vertical stabiliser, rudder, wing tips, flaps and canopy, and did extensive work on the sheared landing gear struts. The three-bladed Sumitomo propeller was dressed and reused. The red hinomaru came off; American stars went on. On 20 September 1942 the aircraft was airworthy.

What Eddie Sanders Found

Lieutenant Commander Eddie R. Sanders flew the Zero 24 times between 20 September and 15 October 1942. The Zero's reputation rested on its agility at low speed and its long range, and Sanders confirmed it deserved both. But he also found that the design had paid for its lightness and slow-speed handling with weaknesses a smart American pilot could exploit.

Sanders reported that the Zero rolled to the left far more easily than to the right. Its float-type carburettor also made the engine cut out under negative g. His advice was blunt: go into a vertical power dive, pushing negative g if possible, and open the range while the Zero's engine was starved. A pursuing Zero pilot who pushed over to follow would lose power at exactly the wrong moment.

The testing did not stop there. The aircraft moved to Anacostia Naval Air Station early in 1943, and in March 1943 went into the Full-Scale Wind Tunnel at the NACA's Langley laboratory under strict secrecy. Test pilots including Frederick M. Trapnell flew it in performance trials and mock dogfights against American fighters.

Period film of a captured Zero being flown by the US Navy in 1942. Video: Aviation videos archives

Treasure, or Just Confirmation?

How much did one Zero really change? Some Japanese assessments were striking. Masatake Okumiya, a naval aviation officer and later a historian, wrote that the capture was "no less serious than the Japanese defeat at Midway" and did much to hasten Japan's final defeat. American ace William N. Leonard agreed.

Historian John Lundstrom pushed back. He argued that Navy pilots at Coral Sea, Midway and Guadalcanal had already worked out how to fight the Zero before any test data reached them, with tactics such as the Thach Weave born in combat. The F6F Hellcat, often said to have been shaped by the Akutan Zero, had already flown in prototype form in June 1942, before Koga's aircraft was even recovered. What the tests did provide was hard numbers and confirmation: exactly where the Zero stopped rolling and why it could not follow a diving American fighter.

The Akutan Zero ended its career as a training aid at North Island. In February 1945 an SB2C Helldiver taxiing nearby lost control and ran into it, and its propeller cut the Zero apart. A few gauges and fragments survive at the National Museum of the United States Navy, the Smithsonian and the Alaska Heritage Museum. Koga's remains were moved to Adak in 1947 and exhumed in 1953, and are believed to have been interred at Chidorigafuchi National Cemetery in Tokyo among unidentified war dead.

A longer documentary on the recovery of the Akutan Zero. Video: Warbirds & Legends

Sources: Wikipedia (Akutan Zero), HISTORY, Smithsonian Channel