NEW ORLEANS -- Marine Lt. Leonard Isaaks Jr. was killed on 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 world at bloody, no-quarter 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 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 story-telling.

Sometime the stories need no elaboration from the photos of men with muddy, bloody faces and haunted eyes. Others emerge in their words. Stories emerge from men with muddy, bloody faces and haunted, like those 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.