The Enola Gay was on its long flight back to its Pacific island base when co-pilot Captain Robert Lewis opened his log and scribbled down the many questions racing through his mind.

"Just how many Japs did we kill?" wondered Lewis after the dazzling silver B-29 bomber dropped the first atomic bomb over Hiroshima, Japan -- and, in doing so, altered the course of history forever.

"I honestly have the feeling of groping for words to explain this... My God, what have we done?" he added in the cursive lettering of the day.

"After a few last looks (at the mushroom cloud), I honestly feel the Japs may give up before we land at Tinian," where Enola Gay was stationed, he said.

"They certainly don't care to have us drop any more bombs of atomic energy like this."

It would be another 27 days -- plus a second nuclear mushroom over Nagasaki -- before Japan surrendered, ending a war that began with its 1937 invasion of China and stretched across the Asia-Pacific region.

Using the atomic bomb, developed amid utmost secrecy, was hugely popular with war-weary Americans at the time -- and 70 years on, a majority today still think it was the right thing to do.

Fifty-six percent of Americans surveyed by the Pew Research Center in February said using the atomic bomb on Japanese cities was justified, compared to 79 percent of Japanese respondents who said it was not.

Were it not for the atomic bomb, many Americans contend, thousands, perhaps hundreds of thousands, maybe millions of American soldiers would have died in a US-led invasion of the Japanese mainland.

-- Muted reference --

At the Smithsonian National Air and Space Museum's vast public collection of historic aircraft near Dulles airport outside Washington, every display gets a succinct 150-word description, including Enola Gay.

It's hard to miss in the vastness of the Udvar-Hazy Center, sharing hanger space with dozens of others planes including an Air France Concorde, the original Boeing 707 prototype and the Space Shuttle Discovery.

"On August 6, 1945, this Martin-built B-29-45-MO dropped the first atomic weapon used in combat on Hiroshima, Japan," its plaque simply notes, with no mention of the death or destruction it sowed.

Twenty years ago, during its restoration, Enola Gay found itself at the center of a firestorm between World War II veterans and a younger generation of historians who questioned the use of "The Bomb."

Veterans and their supporters in Congress alleged that a 50th anniversary exhibition -- with the polished front section of Enola Gay as its star attraction -- depicted the wartime Japanese "more as victims, not aggressors," wrote John Correll of the Air Force Association.

"A package of lies," said Brigadier General Paul Tibbets, Enola Gay's commander, said at the time. "Many are second-guessing the decision to use the atomic weapons. To them I would say: Stop!"

Stunned by the backlash, the Smithsonian reconceived its planned exhibition, titled "The Crossroads: The End of World War II, the Atomic Bomb and the Cold War" at least five times, before it opened in 1995 for a two-year run that drew four million visitors.

By then, the exhibition had been stripped down to a straightforward recounting of the Enola Gay and its historic mission, minus any discussion of the merits or morality of the use of atomic weapons.

"We don't celebrate this artifact as much as we have it here to display," Jeremy Kinney, the Smithsonian's curator of vintage US warplanes, told AFP on the footbridge that passes Enola Gay at cockpit level.

"We try to interpret it as much as we can, and then allow people to interpret it themselves as well. At least that's my take on it, as a curator."

-- Fading away --

Fewer than 855,000 American veterans of World War II are alive today, out of 16 million who served in uniform, and they are fading away at a rate of nearly 500 a day, the National World War II Museum in New Orleans, Louisiana says.

Their dwindling numbers could explain that lack of any furor over an exhibition at American University Museum in Washington of 20 artifacts that survived the Hiroshima and Nagasaki bombings -- objects that were supposed to be part of the 1995 Smithsonian show.

On loan from museums in the two Japanese cities, they include a pupil's scorched uniform, another student's carbonized lunch box and a replica of a pocket watch that stopped at 8:15 -- a replica, because the original is too frail to travel.

"I haven't seen any criticism, really," said Peter Kuznick, an American University history professor and director of its Nuclear Studies Institute who leads annual student trips to Hiroshima and Nagasaki.

Since 1945, he said, a trove of once-classified documents indicates that top US commanders considered the atomic bomb "military unnecessary, morally reprehensible or both," Kuznick told AFP.

Then-president Harry Truman "probably hoped it would speed up a surrender before the Soviets got into the war," and Truman was "obsessed with US-Soviet relations," he said.