Close your eyes and imagine you are a soldier on a landing craft in the first wave of the Allied invasion at Normandy, France, on June 6, 1944. You didn't sleep during the overnight English Channel crossing, and now your stomach is rolling like the waves that continue to splash over the side of the boat.
In your heart is the knowledge that this landing -- and the subsequent fighting ahead -- will free millions of people from an oppressive Third Reich regime of hate and tyranny.
In your mind, though, is the immediacy of hidden German guns, of fierce resistance and of the high likelihood of instant death.
But you charge forward as planned as soon as the ramp lowers.
Imagine that, for a moment.
Time is growing short for participants in that long-ago invasion, the ones who made it through alive. World War II veterans are dying at a rate of 555 per day, according to Veterans Administration figures. But their sacrifice -- and that of each person involved -- should not be taken for granted.
The Tennessee Aquarium IMAX 3D Theater, to mark the 70th anniversary of what became known as D-Day, is offering a new documentary on the event today, Saturday and Sunday at noon and 2 p.m. Veterans will be honored at today's noon showing, which will be introduced by Chattanooga Gen. B.B. Bell and will recognize Signal Mountain Medal of Honor recipient Charles Coolidge. The National Medal of Honor Museum of Military History also will have artifacts on display.
The documentary, in which computer generated imagery is mixed with D-Day film footage, current footage of the French coast and still photography, offers a 45-minute overview of the planning, execution and aftermath of the battle.
"It was the most significant event of World War II," Jim Wade, executive director of the National Medal of Honor Museum, said after screening the film Wednesday. "It was the straw that broke the camel's back. [The film depicts] the enormity of that. [It also shows] the sacrifice of American, British and Canadian troops. The Americans, especially, landed into the teeth of German defensive positions [at Omaha Beach]. The American sacrifice was tremendous."
The documentary, which is narrated by former NBC News anchor and "The Greatest Generation" author Tom Brokaw, describes both the broad facts of the invasion across the eastern Normandy beaches code-named Gold, Juno, Utah, Omaha and Sword, and also its minutiae.
It, for instance, explains the pre-invasion roles of gliders and paratroopers, the weather's role in the invasion date (without a break in the weather, it would have had to be postponed at least two weeks), and the difficulty of the invading troops advancing behind the area's natural -- and, thus, well fortified -- inland hedgerows.
But it also refers to the failed Canadian landing in 1942, the secret sabotage of strategic German transportation routes the night before D-Day, German commander Gen. Erwin Rommel's exit of the area June 5 to return to Germany for his wife's birthday, the undersea oil pipeline laid from England to France to pump gasoline across the channel, and German leader Adolf Hitler's order that he not be awakened until 9 a.m. on the day of the dawn landings.
And the IMAX film salutes the service of both the prominent -- U.S. Gen. Dwight Eisenhower's just-before-invasion letter to his troops is particularly poignant -- and the unknown.
One of the unknowns, a soldier, Melvin, writing home just before the channel crossing, for example, said: "I wonder if I'll be able to forget all this?"
Chances are he didn't, and we shouldn't.
Anniversaries of an event as momentous as D-Day, tagged Operation Overlord by those who'd been planning the invasion for two years, aren't held to glorify war but to mark the accomplishment of a united group of people who believed that freedom was worth the sacrifice.
And what an accomplishment it was, involving more than 160,000 soldiers, sailors and airmen and women, and more than 50,000 vehicles, including 5,000 ships and 11,000 airplanes.
At the end of the first day, 9,000 Allied soldiers died. At the end of 100 days, with the once-picturesque Normandy peninsula considered secure, 200,000 Allied soldiers had died or been wounded. Twice as many Germans died or were injured. Thousands of civilians also lost their lives.
Today, some 18 national leaders -- including President Barack Obama, Russian President Vladamir Putin and German Chancellor Angela Merkel -- and more than 3,000 veterans are expected to attend ceremonies at Sword Beach. May all the leaders grasp what was sacrificed there, and why.