NEW ORLEANS » Marine Lt. Leonard Isaaks Jr. was killed Feb. 20, 1945, during the battle for the Japa­nese island Iwo Jima. All you really need to know about his death is contained in the painstakingly printed letter found on his body:

Dear Daddy,

Merry Christmas. We wish we could all be together. …

Lt. Isaaks’ story is one of many thousands in the National WWII Museum, a whopping 70,000-square-foot repository of America’s collective memory of World War II. Visiting the museum is an intellectually and emotionally walloping passage through a war that took 65 million lives and reshaped politics and culture in ways we are still only beginning to understand.

Much more than a bullets-and-bayonets showcase — though there are plenty of those, too — it’s a riveting tale of terror and bravery, blood and gore, homicide and heroism, starring our parents and grandparents.

They narrate it themselves, through letters they wrote home at the time and oral histories they gave later. Sometimes their horror is wide-eyed: A soldier remembers huddling in a foxhole one long frozen night during the Battle of the Bulge in December 1944, listening to a terribly wounded comrade cry, over and over, "Mother, mother, help" until silenced by a burst of machine-gun fire: "That beseeching plea on that clear, cold Christmas night will remain with me for the rest of my life."

Other times it is disconcertingly matter-of-fact. "We finally hit the beach," recalls a Marine of the 1944 invasion of Japa­nese-held Pele­liu, "but we went through a whole lot of legs, arms and heads."

The museum is a seamless blend of objects and narratives, the latter supplied not only through the usual placards, but also oral histories and short films that can be seen on video consoles scattered through the exhibits. Sometimes it is technologically dazzling — in the four-dimensional film "Beyond All Boundaries," shown hourly, soapy "snowflakes" fall from the ceiling during scenes of the Battle of the Bulge, and electrically wired seats rumble like engines as you watch a segment on bomber missions — but it never lets anything get in the way of storytelling.

Sometime the stories need no elaboration from the photos of men with muddy, bloody faces. Others emerge in their words. Stories emerge from men who became haunted, like that of an emaciated American survivor of the Bataan Death March: "It was something out of, what is it, Dante’s ‘Inferno’? It was hell." Some emerge in grisly chapters: the junior Marine officer who wrote his family from the Pacific that he commanded 46 men but refused to get to know any of them because he didn’t want to order a friend to his death; the junior Army officer at Normandy who saw 23 of his 24 men killed in a single 25-yard stretch of sand.

Even the most mundane artifact in the display cases has a tale to tell. The wristwatch that Pvt. Harold Baumgartner wore as he stormed ashore at Omaha Beach during the D-Day invasion of France looks quite ordinary until you learn that it was practically the only thing on his body that was not shot to pieces — he was wounded five times in two days. A photo of five grinning sailors loses its good cheer when you realize that they were the brothers known as the Fighting Sullivans, all killed in a single attack by a Japa­nese submarine in 1942.

The war’s brutality is not merely implied; it’s shockingly, appallingly explicit. Photos of burned and battered corpses are plentiful. There are shots of Japa­nese soldiers using live Chinese prisoners for bayonet practice and the charred dead left in the rubble of the German city of Dresden after a massive Allied firebombing raid. Mountains of starved, gassed victims of Nazi concentration camps are underlined with the simple words of an American paratrooper who found them: "Now I know why I am here."

A few sections of the museum are posted with warnings that they may be inappropriate for children, but the truth is that there’s hardly any part of it that doesn’t contain disturbing material. Practically nobody gets through it without some tears. Nick Mueller, the former University of New Orleans historian who’s the museum’s president and CEO, makes no apologies for its blunt approach.

"It was a brutal war," he says. "People need to remember that this was a war that was a fight to the finish — for our nation, our democracy, for civilization itself. … Sixty-five million people died in that war, and two-thirds were civilians. That’s a big number, a horrific loss of life. Over 400,000 Americans died; many more were maimed and wounded. We don’t want to glorify that. War isn’t pretty."

But the museum is not without its lighter moments, some ruefully so. A bombardier who flew on Gen. Jimmy Doolittle’s famous 1942 air raid on Tokyo — the first American attack on Japa­nese soil of the war, after a long string of military catastrophes — recounts bailing out of his shot-up plane over China, only to land in a rice paddy generously fertilized with human excrement. "It sounds funny now," he indignantly declares, "but it ain’t funny out there, I can tell you."

A newspaper comic strip published at the end of the war helpfully offers tips to Americans on how to tell apart their Chinese allies and their Japa­nese enemies: "Make them say lalapalooza."

A photo shows a woman smiling wryly as she remembers her soldier husband’s vexed reaction at learning she had liberated herself from keeping house to work in an arms factory.

There is gear issued to soldiers before the D-Day invasion, including packages of condoms ("troops found these useful in keeping sand and water out of rifle barrels," an information panel observes) and a tourism booklet titled "Pocket Guide to France."

There is a Rupert, one of the large dolls dressed as paratroopers and armed with firecrackers dropped into France in an attempt to confuse the German troops about the direction of the Allied attack.

The vast collection of material on D-Day even extends into what might termed alternative history — a handwritten speech that Allied commander Dwight Eisenhower carried in his pocket in case the Normandy invasion was thrown back into the sea: "If any blame or fault attaches to the attempt it is mine alone." Fortunately, it never had to be delivered.

The enormous amount of D-Day content is a remnant of the museum’s origins. It was founded by the late University of New Orleans historian Stephen Ambrose, who while researching a book on the invasion learned that the thousands of landing craft that carried troops and tanks ashore that day had been designed and constructed by New Orleans shipbuilder Andrew Higgins. (Later, when Eisenhower was president, he declared that "Higgins is the man who won the war for us.")

"In 1990, over way too many drinks in Steve’s backyard, we were talking about how nobody knew what an important role New Orleans had played in D-Day," Mueller remembers. "And at the same time, Steve was thinking he needed a place to showcase all the oral histories and photos and other mementos he had collected for the book, and I had been assigned a project to open a research park on the lakefront here. And it all came together.

"Steve said, ‘We’ll have to raise a lot of money. It’ll cost $1 million.’ I said, ‘You’re crazy, it’ll be $4 million.’ And just $30 million and 10 years later, we opened the D-Day Museum for business."

Almost instantly, though, Ambrose and Mueller realized they’d made a mistake. The museum was flooded with visiting World War II vets who loved it but had done their fighting elsewhere than Normandy and wondered why their stories couldn’t be told. And a couple of them, the late U.S. Sens. Ted Stevens (R-Alaska, who served in the China-Burma-India theater) and Daniel Ino­uye (D-Hawaii, who lost an arm fighting in Italy), were in a position to help get government money for a broader museum.

The museum has already added a vast, labyrinthine section on the island-hopping war in the Pacific, including a copy of President Franklin D. Roosevelt’s address to Congress the day after the Japa­nese sneak attack on Pearl Harbor, complete with his handwritten corrections: "a date which will live in world history infamy."

And the museum is two years from the end of a $300 million expansion that will double the floor space for exhibits and add two more buildings to the existing three. They’ll house major exhibits on the war in Africa, on the Asian mainland and the battle for Berlin, as well as more big-ticket weaponry like tanks, planes and even a submarine in which visitors can take part in a simulated attack on a Japa­nese convoy. (Several tanks, halftracks and other armored vehicles already dot the floor of one pavilion, while combat aircraft are suspended from the ceiling.)

The World War II generation, which initially fueled the museum’s popularity, is steadily vanishing. But that hasn’t dimmed the museum’s attraction: March, with 54,000 visitors, was its busiest month ever. Mueller doesn’t expect that to change, because World War II isn’t really history: Its affects on American attitudes toward race and gender and the political boundaries it had redrawn are still evolving.