Legendary pilot Amelia Earhart's disappearance is a decades-old mystery. (Jenny Starrs/The Washington Post)

On July 5, 1937, as the United States was searching the Pacific Ocean for Amelia Earhart’s missing airplane, the State Department got a phone call from the Japanese Embassy in Washington.

Tokyo, the embassy said, wanted to know whether it could help out. Relations between the two countries had been deteriorating since Japan had attacked China in 1931, and were destined to end up with the Japanese bombing Pearl Harbor and the calamity of World War II.

But Greg Bradsher, senior archivist at the National Archives, noted in a new blog post that the Earhart tragedy offered both countries a brief moment of cordiality, which each hoped might lead to better relations.

Earhart’s disappearance roared back into the news this week after the History Channel aired a documentary contending that she survived her last flight and was captured by the Japanese. As proof, the report touted a blurry old photograph that purportedly showed Earhart and her navigator, Fred Noonan, on an atoll in the Marshall Islands.

One problem: A Japanese military history blogger unearthed evidence that the photo was first published in a 1935 Japanese travelogue — two years before Earhart and Noonan set off on their doomed effort to circumnavigate the globe.

Another problem: the Japanese joined the search for the aviator they were supposedly holding captive.

Before her famous flight, Earhart had been a frequent visitor to the White House and was a friend of first lady Eleanor Roosevelt and President Franklin D. Roosevelt, Bradsher wrote Wednesday.

The president was so concerned about Earhart’s disappearance that he kept an open telephone line from Washington to his home in Hyde Park, N.Y. In addition, the White House asked The Washington Post to keep it informed of developments so news could be passed quickly to the president.

In Japan, Prime Minister Fumimaro Konoe and Foreign Minister Koki Hirota probably knew of Earhart’s disappearance on her attempt to fly around the world and probably were behind the overture to the United States. (Both men were to meet grisly ends at the close of World War II.)

Their motives may have been humanitarian, Bradsher wrote. Earhart and Babe Ruth were the best-known Americans in Japan at the time.

But Japan may also have wanted to keep U.S. searchers from poking around “closed” Japanese-controlled islands in the Pacific.

The Navy planned to send the USS Lexington — later destroyed by the Japanese in the 1942 Battle of the Coral Sea — and the USS Colorado to the search area 200 miles north of Howland Island.

But the Japanese had ships that were closer, and offered their help. The United States accepted.

On July 6, Japan radioed all its vessels in the region to join the search for Earhart.

On July 10, Secretary of State Cordell Hull — who would later explode at Japanese diplomats the day Pearl Harbor was attacked — asked Tokyo whether it might search an area where the downed plane could have drifted. Japan said it would do its best. Two days later, Hull expressed his gratitude.

On July 15, the Hull asked the popular Japanese ambassador in Washington, Hiroshi Saito, to “convey to your Government the warmest thanks of the President and myself for the very kind assistance in the search for Miss Earhart.”

“This cooperation and … sympathy on the part of the Japanese Government and people are deeply appreciated,” Hull wrote. “And I wish to assure you of the sincere gratitude of the Government and people of this country.”

Hull had written a member of Congress: “The Earhart disaster may serve, in demonstrating the sympathy of the Japanese … to strengthen the bonds of friendship between the two countries.”

Two years later, when Saito died in Washington, Roosevelt ordered that his ashes be sent home to Japan aboard the modern cruiser USS Astoria, commanded by Capt. Richmond Kelly Turner. The Japanese, in turn, expressed their thanks.

Then came the war.

In 1942, the Astoria was sunk at the Battle of Savo Island in the Pacific, and Turner, then an admiral, went on to direct a string of crushing defeats on Japanese forces in the Pacific.

As for Konoe and Hirota, who had initiated the help in the Earhart search, after the war Konoe killed himself with poison when he was suspected of war crimes, and Hirota was tried for war crimes and hanged.

Read more Retropolis:

Two famed aviators vanished a decade before Amelia Earhart. Their fate remains a mystery, too.

Discovered: Never-before seen photos of Charles Lindbergh’s first Spirit of St. Louis flight

An asteroid was streaking toward Earth. A collision seemed all too possible.

‘Houston, we have a problem’: The amazing history of the iconic Apollo 13 misquote

A young photographer took this harrowing image of the Vietnam War. He didn’t live to see it published.